2021/08/07 更新

写真a

オカダ ケンスケ
岡田 賢祐
OKADA Kensuke
所属
環境生命科学学域 准教授
職名
准教授

学位

  • 博士(学術) ( 2008年3月   岡山大学 )

  • 博士(学術) ( 2008年3月   岡山大学 )

研究キーワード

  • 昆虫学

  • 性選択

  • 生態学

  • 行動学

  • 生態学

研究分野

  • ライフサイエンス / 生態学、環境学

  • ライフサイエンス / 生態学、環境学  / 生態学

学歴

  • 岡山大学   岡山大学大学院環境学研究科  

    2005年4月 - 2008年3月

  • 岡山大学   岡山大学大学院自然科学研究科  

    2003年4月 - 2005年3月

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    国名: 日本国

  • 岡山大学   農学部  

    1999年4月 - 2003年3月

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    国名: 日本国

経歴

  • 岡山大学   大学院環境学生命科学学域   准教授

    2021年4月 - 現在

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    国名:日本国

  • 岡山大学   大学院環境学生命科学研究科   助教

    2012年4月 - 2021年3月

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    国名:日本国

  • 岡山大学   大学院環境学研究科   助教

    2009年4月 - 2012年3月

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    国名:日本国

  • 岡山大学   大学院環境学研究科   日本学術振興会特別研究員

    2008年4月 - 2009年3月

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    国名:日本国

 

論文

  • Natural selection increases female fitness by reversing the exaggeration of a male sexually selected trait

    Kensuke Okada, Masako Katsuki, Manmohan D. Sharma, Katsuya Kiyose, Tomokazu Seko, Yasukazu Okada, Alastair J. Wilson, David J. Hosken

    Nature Communications   12 ( 1 )   2021年12月

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    掲載種別:研究論文(学術雑誌)  

    Theory shows how sexual selection can exaggerate male traits beyond naturally selected optima and also how natural selection can ultimately halt trait elaboration. Empirical evidence supports this theory, but to our knowledge, there have been no experimental evolution studies directly testing this logic, and little examination of possible associated effects on female fitness. Here we use experimental evolution of replicate populations of broad-horned flour beetles to test for effects of sex-specific predation on an exaggerated sexually selected male trait (the mandibles), while also testing for effects on female lifetime reproductive success. We find that populations subjected to male-specific predation evolve smaller sexually selected mandibles and this indirectly increases female fitness, seemingly through intersexual genetic correlations we document. Predation solely on females has no effects. Our findings support fundamental theory, but also reveal unforseen outcomes—the indirect effect on females—when natural selection targets sex-limited sexually selected characters.

    DOI: 10.1038/s41467-021-23804-7

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  • Sexually selected traits and life history traits of larger and smaller males of the horned flour beetle Gnatocerus cornutus

    Katsuya Kiyose, Yasukazu Okada, Masako Katsuki, Y. Suzaki, Kensuke Okada

    Ecological Entomology   46 ( 4 )   807 - 815   2021年8月

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    掲載種別:研究論文(学術雑誌)  

    1. Expression of sexual weapons is strongly affected by environmental factors in armed insects, resulting in a remarkable morphological difference between larger and smaller males. 2. Morphological differences in weapon between larger and smaller males can promote differences in non-sexual traits. This is because weapon sizes are often associated with developments of non-sexual traits such as somatic traits and life history traits. The resulting different subsets of multiple traits may contribute to the reproductive success of larger and smaller males, respectively. 3. There were relatively few studies that couple differences in life history and reproductive traits between larger and smaller males. Here we investigated differences in morphology, behaviours, and life history in Gnatocerus cornutus. 4. Larger males have relatively larger mandibles and the advantage in male fighting to access females. Also, the developmental period was significantly shorter in the larger males than in the smaller males. 5. Smaller males with rudimentary weapons have higher locomotion. This suggests higher performance in the dispersal to new territories. Larger and smaller males showed different suites of multiple traits, and the combinations of multiple traits are probably related to expression of weapons.

    DOI: 10.1111/een.13016

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  • Octopaminergic system orchestrates combat and mating behaviors: A potential regulator of alternative male mating tactics in an armed beetle

    Katsuya Kiyose, Masako Katsuki, Yû Suzaki, Kensuke Okada, Yasukazu Okada

    Journal of Insect Physiology   131   2021年5月

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    掲載種別:研究論文(学術雑誌)  

    Male-male combats over females and territories are widespread across animal taxa. The winner of a combat gains resources, while the loser suffers significant costs (e.g. time, energy and injury) without gaining resources. Many animals have evolved behavioral flexibility, depending on their nutritional condition and experience, to avoid combat in order to reduce such costs. In these cases, male aggression often correlates with mating behavior changes, that is, the deployment of alternative reproductive tactics. Therefore, uncovering the physiological mechanism that orchestrates combat and mating behaviors is essential to understand the evolution of alternative mating tactics. However, so far, our knowledge is limited to specific behaviors (i.e., fighting or mating) of specific model species. In this study, we used an armed beetle (Gnatocerus cornutus) and hypothesized that one of the key neuromodulators of invertebrate aggression, octopamine (OA), would control male combat and other mating behaviors. Using receptor agonists (chlordimeform and benzimidazole), we showed that the octopaminergic (OAergic) system down-regulated the combat and courtship behaviors, while it up-regulated locomotor activity and sperm size. This suggests that the OAergic system orchestrates a suite of fighting and mating behaviors, thereby implying that correlated behavioral responses to OAergic signaling may have driven the evolution of alternative mating tactics in this beetle.

    DOI: 10.1016/j.jinsphys.2021.104211

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  • Older males are more competitive in male fights and more aggressive toward females in the broad-horned flour beetle Gnatocerus cornutus

    Kensuke Okada, Masako Katsuki, Katsuya Kiyose, Yasukazu Okada

    Behavioral Ecology and Sociobiology   74 ( 3 )   2020年3月

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    掲載種別:研究論文(学術雑誌)  

    Abstract: In theory, a male should change the allocation of fighting and mating efforts in relation to his age. Thus, the consequences of sexual selection may be complicated by changes in the male resource allocation due to aging. However, previous studies have focused on changes in female mate choice and male-male competition with aging separately, and the impact of aging on the relationship between mate choice and male competition is unknown. Here, we examined how male competitiveness and attractiveness and their relationship changes over male lifespan in Gnatocerus cornutus. In this species, males perform courtship displays and fight rival males for mates. Older males are more competitive in male fighting and aggressive toward females than younger males. The aggression is also directed toward females. Almost all older males who attacked a female failed to copulate, while younger males never attacked the females. As a result, copulation success decreased with age. When an older male did not mistake a female for a male, he exhibited more frequent courtship. However, mating with older males imposed direct costs on females in terms of both fecundity and lifespan, with no offsetting indirect benefits for her offspring. The courtship behavior of older males does not supply females with cues for mate-choice benefits but are used to coerce females into mating. Our results suggest that male–male competition constrains female preference for older males. Thus, female choice and male–male competition may not be reinforcing in older G. cornutus males. Significance statement: When males get older, they often pay more attention to females in a variety of ways, such as courting and fighting for access. This is because older males have not long to live. In Gnatocerus cornutus as well, older males attend to fighting and courting. The older males seem to be competitive in male fights and attractive to females. However, they are not only aggressive toward rival males but also sometimes use violence on females. As a result, these older males are rejected by the assaulted females and cannot mate. Additionally, the violence of older males can reduce female fecundity and lifespan. Thus, mating with older males is costly to females in G. cornutus, and a female preference for older males is not expected to evolve.

    DOI: 10.1007/s00265-020-2815-4

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  • Mating experience induces females to avoid harmful males in the beetle Lasioderma serricorne

    Kensuke Okada, Yû Suzaki, Rikiya Sasaki, Masako Katsuki

    Animal Behaviour   154   39 - 46   2019年8月

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    掲載種別:研究論文(学術雑誌)  

    When there is sexual conflict over mating rates, males should develop persistence to increase their mating rate, whereas females are expected to evolve resistance to keep mating at a lower rate. In the beetle Lasioderma serricorne, female remating occurs as a result of male persistence, and there is conflict between the sexes over mating rates. However, there is little information on female resistance to the persistence of males. We found that female relocation behaviours were increased by mating experience, but this change in behaviour was not observed in males. Females were also more likely to relocate in the presence of males. To investigate whether the purpose of this change in behaviour is to enable females to avoid males, we assessed how female fitness components changed in relation to two treatments (easy and difficult avoidance). The female remating rate was lower when avoidance was easy, but no difference was observed in the mating rate. In the easy avoidance treatment, we found no difference in fecundity or longevity between females that rejected remating and those that mated only once, while life span was reduced by acceptance of remating. These results indicate that females that rejected remating successfully avoided the harm caused by males by increasing their relocation behaviour. In the difficult avoidance treatment, life span was reduced, irrespective of whether remating was accepted or rejected. In this situation, because they had less opportunity to avoid remating, females might have been more exposed to a second male and thus suffered from harmful persistence. Our results suggest that changes in behaviour after mating are a result of counteradaptation to male persistence because this prevents a decrease in female fitness (female life span) and an increase in male fitness (mating success) in L. serricorne.

    DOI: 10.1016/j.anbehav.2019.06.005

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  • Loser-effect duration evolves independently of fighting ability

    Kensuke Okada, Yasukazu Okada, Sasha R.X. Dall, David J. Hosken

    Proceedings of the Royal Society B: Biological Sciences   286 ( 1903 )   2019年5月

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    掲載種別:研究論文(学術雑誌)  

    Winning or losing contests can impact subsequent competitive behaviour and the duration of these effects can be prolonged. While it is clear effects depend on social and developmental environments, the extent to which they are heritable, and hence evolvable, is less clear and remains untested. Furthermore, theory predicts that winner and loser effects should evolve independently of actual fighting ability, but again tests of this prediction are limited. Here we used artificial selection on replicated beetle populations to show that the duration of loser effects can evolve, with a realized heritability of about 17%. We also find that naive fighting ability does not co-evolve with reductions in the duration of the loser effect. We discuss the implications of these findings and how they corroborate theoretical predictions.

    DOI: 10.1098/rspb.2019.0582

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  • A specific type of insulin-like peptide regulates the conditional growth of a beetle weapon

    Yasukazu Okada, Masako Katsuki, Naoki Okamoto, Haruna Fujioka, Kensuke Okada

    PLoS Biology   17 ( 11 )   2019年

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    掲載種別:研究論文(学術雑誌)  

    Evolutionarily conserved insulin/insulin-like growth factor (IGF) signaling (IIS) has been identified as a major physiological mechanism underlying the nutrient-dependent regulation of sexually selected weapon growth in animals. However, the molecular mechanisms that couple nutritional state with weapon growth remain largely unknown. Here, we show that one specific subtype of insulin-like peptide (ILP) responds to nutrient status and thereby regulates weapon size in the broad-horned flour beetle Gnatocerus cornutus. By using transcriptome information, we identified five G. cornutus ILP (GcorILP1-5) and two G. cornutus insulin-like receptor (GcorInR1, -2) genes in the G. cornutus genome. RNA interference (RNAi)-mediated gene silencing revealed that a certain subtype of ILP, GcorILP2, specifically regulated weapon size. Importantly, GcorILP2 was highly and specifically expressed in the fat body in a condition-dependent manner. We further found that GcorInR1 and Gcor-InR2 are functionally redundant but that the latter is partially specialized for regulating weapon growth. These results strongly suggest that GcorILP2 is an important component of the developmental mechanism that couples nutritional state to weapon growth in G. cornutus. We propose that the duplication and subsequent diversification of IIS genes played a pivotal role in the evolution of the complex growth regulation of secondary sexual traits.

    DOI: 10.1371/journal.pbio.3000541

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  • Temperature variations affect postcopulatory but not precopulatory sexual selection in the cigarette beetle

    Yû Suzaki, Satoko Kodera, Haruhi Fujiwara, Rikiya Sasaki, Kensuke Okada, Masako Katsuki

    Animal Behaviour   144   115 - 123   2018年10月

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    掲載種別:研究論文(学術雑誌)  

    The ambient temperature varies on several timescales such as year, season and day and affects many reproductive traits of ectotherms. Thus, the direction and intensity of sexual selection should be affected by thermal conditions. However, the effects of temperature variation during mating events have sometimes been overlooked. We assessed traits associated with pre- and postcopulatory sexual selection in the cigarette beetle, Lasioderma serricorne, using three thermal mating conditions: 19 °C, 25 °C and 31 °C. Thermal conditions did not affect precopulatory traits (mating rate, mating latency and courtship intensity). Mating duration increased with decreasing temperature, whereas the number of sperm transferred and female fecundity were greatest at 25 °C. To investigate whether these thermal differences affected the risk of sperm competition (remating rate) and fitness consequences for both sexes, we conducted double-mating experiments using a black colour mutant. Females that had first mated at low or high temperatures were more likely to accept remating and exhibited higher fecundity compared to females that rejected remating; when females remated, the paternity of the first male was highest at 25 °C. Thermal conditions at the first mating event affected the fitness consequences for both sexes, irrespective of the females’ remating acceptance. Changes to the thermal conditions for the female remating event caused no difference in the female remating rate or fecundity; however, the paternity of the second mate was highest at the intermediate temperature, and this could be attributed to the decreased sperm transfer at low and high temperatures. Our results suggest that temperature conditions during mating affect postcopulatory processes in L. serricorne. In particular, when females first mated at extreme temperatures, polyandry was promoted, potentially favouring males with higher sperm competitive ability through increased likelihood and intensity of sperm competition.

    DOI: 10.1016/j.anbehav.2018.08.010

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  • Attractive males produce high-quality daughters in the bean bug Riptortus pedestris

    Y. Suzaki, Masako Katsuki, Kensuke Okada

    Entomologia Experimentalis et Applicata   166 ( 1 )   17 - 23   2018年1月

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    掲載種別:研究論文(学術雑誌)  

    There are numerous studies on the genetic benefit of female mate choice. Fisherian benefits are detected frequently, in which attractive males benefit females by increasing the mating success of sons. In contrast, good-genes benefits are relatively small or undetectable, especially as males often face a trade-off between the expression of secondary sexual traits and viability. In this situation, the effects of good genes might be masked in their sons and, therefore, should be investigated in daughters. A previous study has shown that attractive males produce attractive sons (i.e., Fisherian benefit); the present study aimed to verify the existence of good-genes benefits by revealing whether attractive males of the bean bug Riptortus pedestris (Fabricius) (Hemiptera: Alydidae) produced high-quality daughters. Male attractiveness was measured using courtship latency, and the fitness of the females and their offspring was measured based on their lifetime reproductive success as well as the longevity of the daughters. There was no evidence that females directly benefited from mating with attractive males. Whereas male attractiveness (i.e., courtship latency) did not affect nymphal viability or the longevity of daughters, the attractive males with lower courtship latency could produce the daughters with higher lifetime reproductive success. These results suggest that female mating preference in R. pedestris evolved via Fisherian and good-genes benefits.

    DOI: 10.1111/eea.12636

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  • Fitness costs of polyandry to female cigarette beetle Lasioderma serricorne

    Kensuke Okada, Y. Suzaki, Rikiya Sasaki, Masako Katsuki

    Behavioral Ecology and Sociobiology   71 ( 5 )   2017年5月

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    掲載種別:研究論文(学術雑誌)  

    Abstract: Although polyandry is common, it is often unclear why females mate with multiple males. While polyandry may provide females with direct or indirect fitness benefits, it can also be costly. Thus, investigating both the costs and benefits of polyandry is needed to understand the evolution of female polyandry. Here, we investigated the potential benefits and costs of polyandry to females of the cigarette beetle Lasioderma serricorne. We established two treatments: single mating and remating treatments. In the remating treatment, females had the opportunity to remate with a second male. This treatment had two outcomes, that is, acceptance or rejection of mating with the second male. Adult lifespans were shorter in females that accepted and rejected remating than the singly mating female, and there was no difference in lifetime fecundity. This suggests that polyandry is costly to the female and that the cost is due to excessive courting by second mates. Indeed, the direct cost was greater when the second mate was an attractive male. Moreover, we found no difference in offspring quality between females that mated once, accepted, or rejected an additional mating, indicating no indirect benefit of polyandry. Thus, polyandry is thought to carry fitness costs but not benefits to females in L. serricorne. Significance statement: Polyandry, in which females mate with multiple males, often provides females with fitness benefits, but it can sometimes be costly. Because the adaptive significance of polyandry remains controversial, investigating a cost-benefit balance of polyandry is needed to understand the evolution of female multiple mating. Thus, relationships between fitness consequences and polyandry have to be carefully investigated, and we focused on fitness consequences of females that mated singly, accepted, or rejected remating. When females of the cigarette beetle L. serricorne were courted by two males, the female lifespan decreased compared with singly mated female, even if the females did not experience multiple mating. This indicates a direct fitness cost to females due to contact with two males. Additionally, we found no difference in offspring quality between monandrous and polyandrous females. This suggests no indirect benefit of polyandry. In conclusion, polyandry is thought to carry female fitness costs in the cigarette beetle.

    DOI: 10.1007/s00265-017-2316-2

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  • Wolbachia induces costs to life-history and reproductive traits in the moth, Ephestia kuehniella

    Yu Sumida, Masako Katsuki, Kensuke Okada, Keisuke Okayama, Zenobia Lewis

    Journal of Stored Products Research   71   93 - 98   2017年3月

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    掲載種別:研究論文(学術雑誌)  

    The intracellular endosymbiont Wolbachia pipientisis is well-known as one of the most common bacterial symbionts of arthropods. Recently, research has focused on the potential to utilize Wolbachia as a biocontrol agent of agricultural and medical pest insect species. Wolbachia blocks host infection from other pathogens and viruses in some species, however, it can also influence host life-history and reproductive traits. Therefore, in order to understand the biological impact and potential economic utility of Wolbachia, it is necessary to investigate the effects of Wolbachia infection on host traits. We compared life-history and reproductive traits between Wolbachia-infected and cured population in Mediterranean Flour Moth, Ephestia kuehniella. E. kuehniella is well known as a pest of stored products, and when infected with Wolbachia, it exhibits cytoplasmic incompatibility between uninfected females and infected males. We found that E. kuehniella suffers costs as a result of Wolbachia infection, through decreased larval survival and adult longevity, and prolonged developmental period. Moreover, reproductive performance was greater in the uninfected population, when excluding the effect of cytoplasmic incompatibility. Our results indicate that E. kuehniella suffers deleterious effects on both life-history and reproductive traits as a result of being infected with Wolbachia. We suggest such costs should be considered when evaluating the efficacy of utilizing Wolbachia in pest control.

    DOI: 10.1016/j.jspr.2017.02.003

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  • Relationships between male attractiveness, female remating, and sperm competition in the cigarette beetle

    Masako Katsuki, Haruhi Fujiwara, Satoko Kodera, Y. Suzaki, Rikiya Sasaki, Kensuke Okada

    Behavioral Ecology and Sociobiology   71 ( 1 )   2017年1月

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    掲載種別:研究論文(学術雑誌)  

    Abstract: Polyandry creates the opportunity for post-mating sexual selection, and pre- and post-mating sexual selection affects male traits. Investigation of selection pressures in both pre- and post-mating stages is necessary to understand sexual selection. In the cigarette beetle Lasioderma serricorne, we found previously that males that mated faster are thought to be more attractive in the pre-mating process. However, whether the attractive males are favored by the post-mating process remains unclear and thus we set out to investigate this. The attractive males (judged by the pre-mating process) were able to mate sooner with both virgin and non-virgin females. However, attractive males invested less in ejaculation and have difficulty keeping mated females from remating with other males. Thus, under the polyandrous condition, attractive males have a disadvantage in reproductive success due to the risk of sperm competition because they cannot prevent female remating. Therefore, whether a female remates or not would be an important factor in the reproductive success of an attractive male. On the other hand, when a female mated with two males, the last male always sires more offspring, and males who were attractive in pre-mating process did not sire more offspring. These findings suggest that attractive males are at least not favored by the post-mating process itself, and the association between pre- and post-mating sexual selection in L. serricorne is not as simple as reinforcing or undermining. Significance statement: Because females generally mate with multiple males, sexual selection occurs not only before copulation but also after. Thus, investigating the interplay between pre- and post-mating sexual selections is needed to understand sexual selection, but it is still relatively understudied. In the cigarette beetle, males that courted females more were favored by pre-mating processes. Such attractive males had more success mating with virgin and non-virgin females. However, females that have mated with attractive males readily remate with other males, suggesting that the attractive males cannot prevent sperm competition. Thus, the reproductive success of attractive males may be lower under the higher frequency of female remating. Furthermore, non-virgin females were unlikely to bias paternity toward attractive males. These results suggest that males that are favored by pre-mating processes are not favored by post-mating processes in this beetle.

    DOI: 10.1007/s00265-016-2229-5

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  • Histone deacetylases control module-specific phenotypic plasticity in beetle weapons

    Takane Ozawa, Tomoko Mizuhara, Masataka Arata, Masakazu Shimada, Teruyuki Niimi, Kensuke Okada, Yasukazu Okada, Kunihiro Ohta

    Proceedings of the National Academy of Sciences of the United States of America   113 ( 52 )   15042 - 15047   2016年12月

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    Nutritional conditions during early development influence the plastic expression of adult phenotypes. Among several body modules of animals, the development of sexually selected exaggerated traits exhibits striking nutrition sensitivity, resulting in positive allometry and hypervariability distinct from other traits. Using de novo RNA sequencing and comprehensive RNA interference (RNAi) for epigenetic modifying factors, we found that histone deacetylases (HDACs) and polycomb group (PcG) proteins preferentially influence the size of mandibles (exaggerated male weapon) and demonstrate nutrition-dependent hypervariability in the broad-horned flour beetle, Gnatocerus cornutus. RNAi-mediated HDAC1 knockdown (KD) in G. cornutus larvae caused specific curtailment of mandibles in adults, whereas HDAC3 KD led to hypertrophy. Notably, these KDs conferred opposite effects on wing size, but little effect on the size of the core body and genital modules. PcG RNAi also reduced adult mandible size. These results suggest that the plastic development of exaggerated traits is controlled in a module-specific manner by HDACs.

    DOI: 10.1073/pnas.1615688114

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  • Developmental characteristics of the seed bug Graptostethus servus (Hemiptera: Lygaeidae) at different temperatures

    Y. Suzaki, Kensuke Okada

    Applied Entomology and Zoology   51 ( 4 )   555 - 560   2016年11月

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    掲載種別:研究論文(学術雑誌)  

    The effects of temperature on the development and survival of the seed bug Graptostethus servus (Fabricius) were investigated. Eggs and nymphs were reared at temperatures of 20, 22, 25, 28, and 30 °C on seeds of morning glory Ipomoea nil (L.) Roth until adult emergence. Hatchability and nymphal survival rates increased with an increase in temperature. The developmental period was shortened as the temperature increased. The developmental zero and effective accumulated temperature from oviposition to adult emergence were estimated to be 16.3 ± 1.0 °C and 373.6 ± 9.3 degree-days (mean ± SE), respectively. A larger adult body size in both sexes was observed at higher temperatures. Therefore, temperature increase improves larval and adult performance in G. servus.

    DOI: 10.1007/s13355-016-0431-6

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  • Pre and Post-copulatory Selection Favor Similar Genital Phenotypes in the Male Broad Horned Beetle

    Clarissa M. House, M. D. Sharma, Kensuke Okada, David J. Hosken

    Integrative and Comparative Biology   56 ( 4 )   682 - 693   2016年10月

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    掲載種別:研究論文(国際会議プロシーディングス)  

    Sexual selection can operate before and after copulation and the same or different trait(s) can be targeted during these episodes of selection. The direction and form of sexual selection imposed on characters prior to mating has been relatively well described, but the same is not true after copulation. In general, when male-male competition and female choice favor the same traits then there is the expectation of reinforcing selection on male sexual traits that improve competitiveness before and after copulation. However, when male-male competition overrides pre-copulatory choice then the opposite could be true. With respect to studies of selection on genitalia there is good evidence that male genital morphology influences mating and fertilization success. However, whether genital morphology affects reproductive success in more than one context (i.e., mating versus fertilization success) is largely unknown. Here we use multivariate analysis to estimate linear and nonlinear selection on male body size and genital morphology in the flour beetle Gnatocerus cornutus, simulated in a non-competitive (i.e., monogamous) setting. This analysis estimates the form of selection on multiple traits and typically, linear (directional) selection is easiest to detect, while nonlinear selection is more complex and can be stabilizing, disruptive, or correlational. We find that mating generates stabilizing selection on male body size and genitalia, and fertilization causes a blend of directional and stabilizing selection. Differences in the form of selection across these bouts of selection result from a significant alteration of nonlinear selection on body size and a marginally significant difference in nonlinear selection on a component of genital shape. This suggests that both bouts of selection favor similar genital phenotypes, whereas the strong stabilizing selection imposed on male body size during mate acquisition is weak during fertilization.

    DOI: 10.1093/icb/icw079

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  • Costs and benefits of symbiosis between a bean beetle and Wolbachia

    Keisuke Okayama, Masako Katsuki, Yu Sumida, Kensuke Okada

    Animal Behaviour   119   19 - 26   2016年9月

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    掲載種別:研究論文(学術雑誌)  

    Wolbachia are a major symbiont of arthropods and nematodes. They can manipulate host reproduction in order to spread in host populations, but Wolbachia manipulation often incurs costs to the host species itself and/or provides benefits to the host. Because the fitness effects of Wolbachia infections differ between host species, fitness components of the host have to be carefully investigated. However, it is still relatively understudied. Here, we investigated effects of Wolbachia infection on life history and reproductive traits in Callosobruchus chinensis. This is a host in which the prevalence of Wolbachia and the cytoplasmic incompatibility (CI) it causes have been well reported. However, excluding research related to CI, there is little information about the effects of Wolbachia infection on traits of C. chinensis. We found that Wolbachia infection had positive effects on the life history and reproductive traits of C. chinensis males and females, with the exception of a negative effect on female fecundity. Nevertheless, Wolbachia-infected females are thought to have the advantage of reproduction because of complete CI in eggs from an uninfected female mated with an infected male. These results suggest that Wolbachia infection affects the life history and sexual selection of C. chinensis populations.

    DOI: 10.1016/j.anbehav.2016.07.004

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  • Molecular cloning and functional characterization of the sex-determination gene doublesex in the sexually dimorphic broad-horned beetle Gnatocerus cornutus (Coleoptera, Tenebrionidae)

    Hiroki Gotoh, Mai Ishiguro, Hideto Nishikawa, Shinichi Morita, Kensuke Okada, Takahisa Miyatake, Toshinobu Yaginuma, Teruyuki Niimi

    Scientific Reports   6   2016年7月

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    掲載種別:研究論文(学術雑誌)  

    Various types of weapon traits found in insect order Coleoptera are known as outstanding examples of sexually selected exaggerated characters. It is known that the sex determination gene doublesex (dsx) plays a significant role in sex-specific expression of weapon traits in various beetles belonging to the superfamily Scarabaeoidea. Although sex-specific weapon traits have evolved independently in various Coleopteran groups, developmental mechanisms of sex-specific expression have not been studied outside of the Scarabaeoidea. In order to test the hypothesis that dsx-dependent sex-specific expression of weapon traits is a general mechanism among the Coleoptera, we have characterized the dsx in the sexually dimorphic broad-horned beetle Gnatocerus cornutus (Tenebrionidea, Tenebirionidae). By using molecular cloning, we identified five splicing variants of Gnatocerus cornutus dsx (Gcdsx), which are predicted to code four different isoforms. We found one male-specific variant (GcDsx-M), two female-specific variants (GcDsx-FL and GcDsx-FS) and two non-sex-specific variants (correspond to a single isoform, GcDsx-C). Knockdown of all Dsx isoforms resulted in intersex phenotype both in male and female. Also, knockdown of all female-specific isoforms transformed females to intersex phenotype, while did not affect male phenotype. Our results clearly illustrate the important function of Gcdsx in determining sex-specific trait expression in both sexes.

    DOI: 10.1038/srep29337

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  • Macronutrient balance mediates the growth of sexually selected weapons but not genitalia in male broad-horned beetles

    Clarissa M. House, Kim Jensen, James Rapkin, Sarah Lane, Kensuke Okada, David J. Hosken, John Hunt

    Functional Ecology   30 ( 5 )   769 - 779   2016年5月

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    掲載種別:研究論文(学術雑誌)  

    Condition is defined as the pool of resources available to an individual that can be allocated to fitness-enhancing traits. Consequently, condition could influence developmental trade-offs if any occur. Although many studies have manipulated diet to demonstrate condition-dependent trait expression, few studies have determined the contribution of specific nutrients to condition or trade-offs. We used nutritional geometry to quantify the effects of dietary protein and carbohydrate content on larval performance and the development of adult morphology including body size as well as a primary and secondary sexually selected trait in male broad-horned beetles, Gnatocerus cornutus. We found that offspring survival, development rate and morphological traits were highly affected by dietary carbohydrate content and to a lesser extent by protein content and that all traits were maximized at a protein-to-carbohydrate ratio around 1:2. The absolute size of a secondary sexual character, the mandibles, had a heightened response to the increased availability and ratio of both macronutrients. Male genitalia, in contrast, were relatively insensitive to the increased availability of macronutrients. Overall, while nutrition influenced trait expression, the nutritional requirements of development rate and morphological traits were largely the same and resource acquisition seems to implement only weak trade-offs in this species. This finding contrasts with some resource constraint predictions, as beetles seem able to simultaneously meet the nutritional requirements of most traits.

    DOI: 10.1111/1365-2435.12567

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  • Competitive males but not attractive males reduce female fitness in Gnatocerus cornutus

    Katsuya Kiyose, Masako Katsuki, Yû Suzaki, Kensuke Okada

    Animal Behaviour   109   265 - 272   2015年11月

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    掲載種別:研究論文(学術雑誌)  

    General concepts of sexual selection assume that females benefit from mating with more competitive or attractive males. By contrast, sexual conflict theory assumes that females suffer greater costs from mating with such males. To understand how mate choice evolves, it is necessary to examine these different predictions regarding costs and benefits. Moreover, environmental factors may play an important role in the consequences of mate choice benefits. Here, we examined how mate choice benefits and sexual conflict costs are affected by an environmental condition (single or repeated interaction with a mate) in Gnatocerus cornutus (Coleoptera: Tenebrionidae). The males have enlarged mandibles to fight rivals and for courtship display to attract mates, and these characters provide a mating advantage to males. In G. cornutus, compared with a single mating, continuous housing with a male directly enhances female fitness due to increased mating frequency and sperm replenishment. In a single mating situation, there were neither direct benefits nor costs from competitive and attractive males. By contrast, when females were continuously housed with a competitively superior male, female fitness was reduced, probably because of misdirected attacks by the competitive male. Thus, our result suggests that females suffer direct costs from competitive males in G. cornutus but this cost is not incurred when there are few sexual interactions.

    DOI: 10.1016/j.anbehav.2015.09.002

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  • Polyandry and fitness in female horned flour beetles, Gnatocerus cornutus

    Kensuke Okada, C. Ruth Archer, Masako Katsuki, Yû Suzaki, Manmohan D. Sharma, Clarissa M. House, David J. Hosken

    Animal Behaviour   106   11 - 16   2015年8月

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    掲載種別:研究論文(学術雑誌)  

    Although polyandry is common, it is often unclear why females mate with multiple males, because although polyandry may provide females with direct or indirect fitness benefits, it can also be costly. Our understanding of polyandry is also restricted by the relative paucity of studies that disentangle the fitness effects of mating more than once with a single male and mating with multiple males. Here we investigated potential benefits and costs of polyandry in the horned beetle, Gnatocerus cornutus, while controlling for the number of matings. We found that female life span was independent of mating frequency, indicating that mating itself is not very costly. However, females that mated more than once laid more eggs and had greater lifetime reproductive success than singly mated females. Because the magnitude of these effects was similar in monandrous and polyandrous females, this improved fertility was due to multiple mating itself, rather than mating with multiple males. However, although polyandrous females produced more attractive sons, these males tended to have smaller mandibles and so may fare less well in male-male competition. The se results indicate that polyandry is relatively cost free, at least in the laboratory, and has direct and indirect benefits to female fitness. However, because the attractive sons produced by polyandrous females may fight less well, the indirect benefits of polyandry will depend on the intensity of male-male competition and how free females are to exert mate choice. Where competition between males is intense, polyandry benefits via son attractiveness may be reduced and perhaps even carry costs to female fitness.

    DOI: 10.1016/j.anbehav.2015.05.008

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  • Environmental factors affecting pupation decision in the horned flour beetle gnatocerus cornutus

    Takane Ozawa, Kunihiro Ohta, Masakazu Shimada, Kensuke Okada, Yasukazu Okada

    Zoological Science   32 ( 2 )   183 - 187   2015年4月

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    掲載種別:研究論文(学術雑誌)  

    Social environments often affect the development of organisms. In Tenebrionidae beetles, larval development can be arrested at the final instar stage in the presence of conspecific larvae. This developmental plasticity is considered to be an anti-cannibalistic strategy but the critical environmental determinants and actual effects remain to be elucidated. In this study, we examined the effects of the heterospecific environment, conspecific sexual environment (i.e., presence of conspecific male or female), and abiotic physical stimulation on the pupation decision of the sexually dimorphic horned-flour beetle Gnatocerus cornutus. Additionally, actual anti-cannibalistic or antipredatory effects of developmental arrest were evaluated by analyzing stage-dependent vulnerabilities. When G. cornutus larvae were maintained with a G. cornutus larva, a G. cornutus adult, or T. castaneum adult, the developmental period up to the prepupal stage was significantly elongated, suggesting that the cue is not species-specific. Sexual environment did not affect the timing of pupation in G. cornutus; however, we found that abiotic tactile stimulations by glass beads could repress pupation. We also discovered that prepupal and pupal stages were more vulnerable to cannibalism and predation than the larval stage. These data suggest that G. cornutus larvae use non-species specific tactile stimulation as a decision cue for pupation and it has broader defensive effects against heterospecific predation as well as conspecific cannibalism.

    DOI: 10.2108/zs140203

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  • Sex-specific effects of natural and sexual selection on the evolution of life span and ageing in Drosophila simulans

    C. Ruth Archer, Eoin Duffy, David J. Hosken, Mikael Mokkonen, Kensuke Okada, Keiko Oku, Manmohan D. Sharma, John Hunt

    Functional Ecology   29 ( 4 )   562 - 569   2015年4月

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    掲載種別:研究論文(学術雑誌)  

    Variation in the strength of age-dependent natural selection shapes differences in ageing rates across species and populations. Likewise, sexual selection can promote divergent patterns of senescence across the sexes. However, the effects of these processes on the evolution of ageing have largely been considered independently, and interactions between them are poorly understood. We use experimental evolution to investigate how natural and sexual selection affect life span and ageing in Drosophila simulans. Replicate populations were evolved under lifetime monogamy (relaxed sexual selection) or lifetime polyandry (elevated sexual selection) and at one of two temperatures, 25 °C (relaxed natural selection) or 27 °C (enhanced natural selection), in a fully factorial design. We measured longevity in 150 individually housed flies taken from each of three replicate populations per selection regime. We found that natural and sexual selection affected the evolution of life span via sex-specific effects on different ageing parameters (ageing rate vs. baseline mortality): natural selection reduced the rate of ageing in both sexes but increased male baseline mortality, while sexual selection elevated baseline mortality in both sexes but particularly in males. This means that sexual and natural selection interacted to reduce male life span but acted on female life span by independently affecting particular ageing parameters. Sex-specific effects of sexual and natural selection may help explain the diverse patterns of ageing seen in nature but complicate predictions about how ageing and life span evolve across the sexes.

    DOI: 10.1111/1365-2435.12369

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  • Rival male chemical cues evoke changes in male pre- and post-copulatory investment in a flour beetle

    Sarah M. Lane, Joanna H. Solino, Christopher Mitchell, Jonathan D. Blount, Kensuke Okada, John Hunt, Clarissa M. House

    Behavioral Ecology   26 ( 4 )   1021 - 1029   2015年

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    掲載種別:研究論文(学術雑誌)  

    Males can gather information on the risk and intensity of sperm competition from their social environment. Recent studies have implicated chemosensory cues, for instance cuticular hydrocarbons (CHCs) in insects, as a key source of this information. Here, using the broad-horned flour beetle (Gnatocerus cornutus), we investigated the importance of contact-derived rival male CHCs in informing male perception of sperm competition risk and intensity. We experimentally perfumed virgin females with male CHCs via direct intersexual contact and measured male pre- and post-copulatory investment in response to this manipulation. Using chemical analysis, we verified that this treatment engendered changes to perfumed female CHC profiles, but did not make perfumed females "smell" mated. Despite this, males responded to these chemical changes. Males increased courtship effort under low levels of perceived competition (from 1-3 rivals), but significantly decreased courtship effort as perceived competition rose (from 3-5 rivals). Furthermore, our measurement of ejaculate investment showed that males allocated significantly more sperm to perfumed females than to control females. Together, these results suggest that changes in female chemical profile elicited by contact with rival males do not provide males with information on female mating status, but rather inform males of the presence of rivals within the population and thus provide a means for males to indirectly assess the risk of sperm competition.

    DOI: 10.1093/beheco/arv047

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  • Sexual conflict over mating in Gnatocerus cornutus? Females prefer lovers not fighters

    Kensuke Okada, Masako Katsuki, Manmohan D. Sharma, Clarissa M. House, David J. Hosken

    Proceedings of the Royal Society B: Biological Sciences   281 ( 1785 )   2014年5月

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    掲載種別:研究論文(学術雑誌)  

    Female mate choice and male-male competition are the typical mechanisms of sexual selection. However, these two mechanisms do not always favour the same males. Furthermore, it has recently become clear that female choice can sometimes benefit males that reduce female fitness. So whether male- male competition and female choice favour the same or different males, and whether or not females benefit from mate choice, remain open questions. In the horned beetle, Gnatocerus cornutus, males have enlarged mandibles used to fight rivals, and larger mandibles provide a mating advantage when there is direct male-male competition for mates. However, it is not clear whether females prefer these highly competitive males. Here, we show that female choice targets male courtship rather than mandible size, and these two characters are not phenotypically or genetically correlated. Mating with attractive, highly courting males provided indirect benefits to females but only via the heritability of male attractiveness. However, mating with attractive males avoids the indirect costs to daughters that are generated by mating with competitive males. Our results suggest that male-male competition may constrain female mate choice, possibly reducing female fitness and generating sexual conflict over mating. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

    DOI: 10.1098/rspb.2014.0281

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  • Which wavelength does the cigarette beetle, Lasioderma serricorne (Coleoptera: Anobiidae), prefer? Electrophysiological and behavioral studies using light-emitting diodes (LEDs)

    Masako Katsuki, Kentaro Arikawa, Motohiro Wakakuwa, Yusuke Omae, Kensuke Okada, Rikiya Sasaki, Kazutaka Shinoda, Takahisa Miyatake

    Applied Entomology and Zoology   48 ( 4 )   547 - 551   2013年11月

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    掲載種別:研究論文(学術雑誌)  

    The cigarette beetle, Lasioderma serricorne (Fabricius), is an important pest insect that consumes a variety of dry foods. It is known that UV light traps attract this species. However, less attention has been paid to its preferred wavelength. First, we investigated the spectral sensitivity of the compound eye. Next, we compared the attraction efficiency of LEDs of different colors (wavelengths). Our results showed that ultraviolet (UV, 375 nm) and blue (470 nm) LEDs attracted the most cigarette beetles of both sexes, irrespective of mating or oviposition status, although the UV LED consistently tended to attract the most beetles. Although the primary sensitivity peak of the compound eye was 520 nm, the green LED (520 nm) scarcely attracted beetles. Although the reason for the difference between the peaks in spectral sensitivity and attraction of beetles awaits further studies, whether UV and/or blue LEDs is more effective as a practical light trap for controlling L. serricorne beetle is discussed in this study. © 2013 The Japanese Society of Applied Entomology and Zoology.

    DOI: 10.1007/s13355-013-0205-3

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  • Inter- and intrasexual genetic correlations of exaggerated traits and locomotor activity

    T. Fuchikawa, K. Okada

    Journal of Evolutionary Biology   26 ( 9 )   1979 - 1987   2013年9月

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    Exaggerated traits in males can be costly and therefore can negatively affect fitness. Although these costs are thought to be male specific, traits that have a negative effect due to exaggeration are often shared between the sexes as life-history traits. When there are genetic intersexual correlations for these shared characters, the evolution of the exaggerated traits can impose these costs on nonadorned females through the intersexual correlation. Thus, the exaggerated traits can constrain optimum development of female characters, even if the females lack these exaggerations completely. However, investigation of this pattern has been largely ignored, and thus, it is necessary to investigate genetic architectures of these traits within and across the sexes. Male flour beetles, Gnatocerus cornutus, have enlarged mandibles that are used in male-male competition, but females lack this character completely. Using a traditional full-sib/half-sib breeding design, we detected a negative intrasexual genetic correlation between male weapon size and locomotor activity, but not an intersexual genetic correlation for locomotor activity. After subjecting this weapon to 17 generations of bidirectional selection, we found a correlated response to locomotor activity in the male, whereas there was no correlated response in the female. Our results suggest that the costs of exaggerated traits to locomotion are not imposed on females and would be male specific. This is partly explained by genetic decoupling of locomotor activities across the sexes. © 2013 The Authors. Journal of Evolutionary Biology © 2013 European Society For Evolutionary Biology.

    DOI: 10.1111/jeb.12197

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  • Pre-copulatory sexual selection in the cigarette beetle Lasioderma serricorne

    Kensuke Okada, Taro Fuchikawa, Yusuke Omae, Masako Katsuki

    Behavioral Ecology and Sociobiology   67 ( 1 )   53 - 59   2013年1月

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    掲載種別:研究論文(学術雑誌)  

    Traditional concepts of sexual selection and sexual conflict make different predictions about the costs and benefits to females of exposure to males with higher mating success. The traditional concepts of sexual selection assume that females benefit from their mate choices, whereas sexual conflict assumes that the females suffer greater costs by mating with males who have greater mating success and thus reduce their fitness. In order to understand how mate choice evolves, it is necessary to estimate the overall effect of mate choice on female fitness. However, relatively few studies have conducted that investigation. In this study, we investigated the direct and indirect effects of mating with attractive males on the fitness of females in the cigarette beetle Lasioderma serricorne. Mating with attractive males increased the number of female offspring but did not affect female longevity. Additionally, we found evidence that attractive males sire highly attractive sons. Thus, mating with an attractive male provides direct and indirect benefits but no fitness cost to female L. serricorne. © 2012 Springer-Verlag Berlin Heidelberg.

    DOI: 10.1007/s00265-012-1424-2

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  • Impacts of diet quality on life-history and reproductive traits in male and female armed beetle, Gnatocerus cornutus

    Masako Katsuki, Yasukazu Okada, Kensuke Okada

    Ecological Entomology   37 ( 6 )   463 - 470   2012年12月

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    掲載種別:研究論文(学術雑誌)  

    1. The energy available for reproduction is usually limited by resource acquisition (i.e. condition). Because condition is known to be strongly affected by environmental factors, reproductive investments also vary across heterogeneous environments. 2. Although the condition dependence of reproductive investment is common to both sexes, reproductive traits may exhibit sexually different responses to environmental fluctuation due to sex-specific life-history strategies. However, few direct experimental studies have investigated the condition dependence of reproductive investments in both sexes. 3. We investigated the condition dependence of life-history and reproductive traits of males and females in the beetle Gnatocerus cornutus Fabricus by manipulating larval and adult diet quality. We found that male and female life-history traits exhibited similar responses to environmental fluctuations. 4. By contrast, the sexes exhibit different patterns of condition dependence in reproductive traits (i.e. the adult nutritional environment has a strong impact on the female lifetime reproductive success, whereas larval nutritional environment strongly affects the secondary sexual trait in males). 5. This difference in the plasticity of reproductive traits may lead to different selection pressures for each sex, even if both sexes develop and/or live in the same environment. © 2012 The Royal Entomological Society.

    DOI: 10.1111/j.1365-2311.2012.01390.x

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  • Erratum to: Ultraviolet light-emitting diode (UV LED) trap for the West Indian sweet potato weevil, Euscepes postfasciatus (Coleoptera: Curculionidae) (Appl Entomol Zool, (2012), 47, (285-290), 10.1007/s13355-012-0113-y)

    Masako Katsuki, Yusuke Omae, Kensuke Okada, Toru Kamura, Takashi Matsuyama, Dai Haraguchi, Tsuguo Kohama, Takahisa Miyatake

    Applied Entomology and Zoology   47 ( 4 )   481   2012年11月

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    DOI: 10.1007/s13355-012-0140-8

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  • Ultraviolet light-emitting diode (UV LED) trap the West Indian sweet potato weevil, Euscepes postfasciatus (Coleoptera: Curculionidae)

    Masako Katsuki, Yusuke Omae, Kensuke Okada, Toru Kamura, Takashi Matsuyama, Dai Haraguchi, Tsuguo Kohama, Takahisa Miyatake

    Applied Entomology and Zoology   47 ( 3 )   285 - 290   2012年8月

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    掲載種別:研究論文(学術雑誌)  

    The West Indian sweet potato weevil Euscepes postfasciatus (Fairmaire) is a troublesome pest insect of sweet potato that originally came from the Caribbean, but is now expanding its distribution into the Pacific Islands. Although sterile insect techniques have been used against this pest in a demonstration experiment on Kume Island [Ohno et al. (2006) Kontyu to Shizen 41:25-30], effective methods of monitoring E. postfasciatus are scarce. It is necessary to detect the weevils at an early stage of invasion in uninvaded areas, and an attractant trap can be used to achieve this. Thus, we developed an ultraviolet (UV) light-emitting diode trap, invented a method for diffusing the light to attract more insects, and investigated the attractiveness of the light trap to E. postfasciatus under laboratory conditions. Our results indicate that diffused UV light has a higher potential to attract E. postfasciatus than direct UV light. Furthermore, sweet potato is an effective bait to use to capture the weevils attracted by UV light. Thus, E. postfasciatus can be trapped using diffused UV light and sweet potato bait. © 2012 The Japanese Society of Applied Entomology and Zoology.

    DOI: 10.1007/s13355-012-0113-y

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  • Juvenile hormone mediates developmental integration between exaggerated traits and supportive traits in the horned flour beetle Gnatocerus cornutus

    Yasukazu Okada, Hiroki Gotoh, Toru Miura, Takahisa Miyatake, Kensuke Okada

    Evolution and Development   14 ( 4 )   363 - 371   2012年7月

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    掲載種別:研究論文(学術雑誌)  

    Sexually selected exaggerated traits are often coupled with modifications in other nontarget traits. In insects with weapons, enlargements of nontarget characters that functionally support the weapon often occur (i.e. supportive traits). The support of sexual traits requires developmental coordination among functionally related multiple traits-an explicit example of morphological integration. The genetic theory predicts that developmental integration among different body modules, for which development is regulated via different sets of genes, is likely to be coordinated by pleiotropic factors. However, the developmental backgrounds of morphological integrations are largely unknown. We tested the hypothesis that the juvenile hormone (JH), as a pleiotropic factor, mediates the integration between exaggerated and supportive traits in an armed beetle Gnatocerus cornutus. During combat, males of this beetle use exaggerated mandibles to lift up their opponents with the supportive traits, that is, the head and prothoracic body parts. Application of methoprene, a JH analog (JHA), during the larval to prepupal period, induced the formation of large mandibles relative to the body sizes in males. Morphometric examination of nontarget traits elucidated an increase in the relative sizes of supportive traits, including the head and prothoracic body parts. In addition, reductions in the hind wing area and elytra length, which correspond to flight and reproductive abilities, were detected. Our findings are consistent with the genetic theory and support the idea that JH is a key pleiotropic factor that coordinates the developmental integration of exaggerated traits and supportive characters, as well as resource allocation trade-offs. © 2012 Wiley Periodicals, Inc.

    DOI: 10.1111/j.1525-142X.2012.00554.x

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  • Life history and mating behavior of a black-bodied strain of the cigarette beetle Lasioderma serricorne (Coleoptera: Anobiidae)

    Yusuke Omae, Taro Fuchikawa, Satoshi Nakayama, Kensuke Okada, Takahisa Miyatake, Rikiya Sasaki, Kazutaka Shinoda

    Applied Entomology and Zoology   47 ( 2 )   157 - 163   2012年5月

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    掲載種別:研究論文(学術雑誌)  

    Adults of the cigarette beetle, Lasioderma serricorne (Fabricius), usually have brownish-red bodies. In this study, we selected for black body color and established a black body strain as a genetic marker. Subsequently, we conducted experimental crosses and discovered that the black body color was characterized by recessive inheritance. Moreover, we observed no difference between the mating behavior and life history of the black strain and normal beetles. On the basis of these results, our black strain could be a mutant in which only adult body color is genetically changed. Thus, our strain is thought to be a useful genetic marker to improve pest control methods for L. serricorne. © 2012 The Japanese Society of Applied Entomology and Zoology.

    DOI: 10.1007/s13355-012-0103-0

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  • Effect of weapon-supportive traits on fighting success in armed insects

    Yasukazu Okada, Yû Suzaki, Takahisa Miyatake, Kensuke Okada

    Animal Behaviour   83 ( 4 )   1001 - 1006   2012年4月

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    掲載種別:研究論文(学術雑誌)  

    Male fighting frequently results in the evolution of traits used as weapons. These are often coupled with correlated modifications in other somatic traits (hereafter referred to as supportive traits), which are thought to support the weapon functionally. No previous studies have investigated whether supportive traits themselves affect fighting success. We evaluated this possibility in two armed insects, the beetle . Gnatocerus cornutus and the bug . Riptortus pedestris. Using a principal components analysis, we identified a subset of supportive traits that were associated with weapons in both species. The patterns of supportive structures differed between the two species, probably reflecting differences in the use of weapons during fights. In both species, fighting success was higher in males with enhanced supportive traits. It appears that weapon-supportive structures develop as the result of selection that favours coordination among multiple traits associated with fighting behaviour. Thus, our results provide rare evidence of the benefit of a supportive trait that is a clear example of phenotypic integration. © 2012 The Association for the Study of Animal Behaviour.

    DOI: 10.1016/j.anbehav.2012.01.021

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  • Intralocus sexual conflict and offspring sex ratio

    Masako Katsuki, Tomohiro Harano, Takahisa Miyatake, Kensuke Okada, David J. Hosken

    Ecology Letters   15 ( 3 )   193 - 197   2012年3月

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    掲載種別:研究論文(学術雑誌)  

    Males and females frequently have different fitness optima for shared traits, and as a result, genotypes that are high fitness as males are low fitness as females, and vice versa. When this occurs, biasing of offspring sex-ratio to reduce the production of the lower-fitness sex would be advantageous, so that for example, broods produced by high-fitness females should contain fewer sons. We tested for offspring sex-ratio biasing consistent with these predictions in broad-horned flour beetles. We found that in both wild-type beetles and populations subject to artificial selection for high- and low-fitness males, offspring sex ratios were biased in the predicted direction: low-fitness females produced an excess of sons, whereas high-fitness females produced an excess of daughters. Thus, these beetles are able to adaptively bias sex ratio and recoup indirect fitness benefits of mate choice. © 2012 Blackwell Publishing Ltd/CNRS.

    DOI: 10.1111/j.1461-0248.2011.01725.x

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  • Comparison of two polymorphic sites in the clock gene cryptochrome in the Taiwan strain of the melon fly, Bactrocera cucurbitae (Diptera: Tephritidae): A possible quick method to estimate the mating time of trapped invading flies

    Taro Fuchikawa, Takashi Matsuyama, Masaaki Yamagishi, Satoshi Nakayama, Kensuke Okada, Takahisa Miyatake

    Applied Entomology and Zoology   46 ( 4 )   553 - 557   2011年11月

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    掲載種別:研究論文(学術雑誌)  

    For successful sterile insect technique (SIT), synchronized copulation between invaded females and sterilized males is required. Understanding the mating time of the invaded strain is an aid in synchronizing and thus improving the effectiveness of SIT. We previously demonstrated a relationship between variation at two sites of a circadian clock gene cryptochrome (cry) (cry1212 and cry1865) and circadian behavior in the melon fly Bactrocera cucurbitae (Coquillett). Here we investigated the relationship in two other populations, Taiwan1 (T1) and Taiwan2 (T2), which may re-invade Okinawa. The results showed that T1 exhibited a lower frequency of the S-type allele, which was observed in early mating flies in the strains in Okinawa, than T2 at the site of cry1212. In addition, T1 showed a longer circadian period than T2. We also noted that the cry1212 site showed higher amino acid sequence conservation than cry1865 by comparing CRY1 among five insect species. These results suggest that genotyping of only the cry1212 site of trapped flies enables an immediate estimate of the mating time of the B. cucurbitae population from Taiwan and that cry1212 would be more likely to be involved in determining the mating time than cry1865. © 2011 The Japanese Society of Applied Entomology and Zoology.

    DOI: 10.1007/s13355-011-0075-5

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  • Longevity, calling effort, and metabolic rate in two populations of cricket

    Kensuke Okada, William R. Pitchers, Manmohan D. Sharma, John Hunt, David J. Hosken

    Behavioral Ecology and Sociobiology   65 ( 9 )   1773 - 1778   2011年9月

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    掲載種別:研究論文(学術雑誌)  

    Intraspecific variation in a resting metabolic rate (RMR) is likely to be an important determinant of energetic-resource use and may influence the resources subsequently available for allocation to traits not directly associated with somatic maintenance. The influence of RMR on resource availability could be especially important for condition-dependent sexual traits, such as cricket calls, that are themselves energetically costly to produce. RMR may also be associated with longevity, either negatively because individuals with a high RMR burn resources faster and die young, or positively as individuals with high RMR are more able to accrue resources to fuel survival. Additionally, the associations between RMR and other characters may vary across populations if differential selection or drift shapes these traits. Here we tested for differences in RMR, body mass, calling effort, and longevity in two populations of cricket Gryllodes sigillatus and then evaluated the potential influence of RMR on calling and longevity. We find that RMR, calling effort, and longevity varied across populations, but mass did not. Controlling for population and mass, RMR was not significantly associated with calling effort, but was negatively associated with longevity. These findings suggest that male crickets that live fast die young. © 2011 Springer-Verlag.

    DOI: 10.1007/s00265-011-1185-3

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  • Male aggressive behavior and exaggerated hindlegs of the bean bug riptortus pedestris

    Kensuke Okada, Yû Suzaki, Yasukazu Okada, Takahisa Miyatake

    Zoological Science   28 ( 9 )   659 - 663   2011年9月

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    掲載種別:研究論文(学術雑誌)  

    Males of the bean bug species Riptortus pedestris possess larger hindlegs than females. Observations of male-male interactions showed that the enlarged hindlegs are used as weapons in male fights, and that males with larger hindlegs win fights more frequently. Morphological analysis based on the positive allometry test showed that the femora of larger males are relatively bigger than those of smaller males, but femora of larger females are not relatively larger than those of smaller females. These results suggest that sexual selection in R. pedestris favors larger hindlegs for male fighting. In addition, the thorax and abdomen lengths were larger in the male than in the female. The males often lift their abdomen with their back to the opponent for displays against an opponent. As a result, abdominal size may be under stronger selection in the male than in the female, as for the exaggerated hindlegs. © 2011 Zoological Society of Japan.

    DOI: 10.2108/zsj.28.659

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  • Immature performance linked with exaggeration of a sexually selected trait in an armed beetle

    Kensuke Okada, M. Katsuki, Y. Okada, T. Miyatake

    Journal of Evolutionary Biology   24 ( 8 )   1737 - 1743   2011年8月

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    掲載種別:研究論文(学術雑誌)  

    Exaggerated traits can be costly and are often trade-off against other characters, such as life-history traits. Thus, the evolution of an exaggerated trait is predicted to affect male life-history strategies. However, there has been very little experimental evidence of the impact of the evolution of sexually selected traits on life-history traits. This study investigated whether increased investment in exaggerated traits can generate evolutionary changes in the life-history strategy for armed males. Male flour beetles, Gnatocerus cornutus, have enlarged mandibles that are used in male-male competition, but females lack this character exaggeration completely. We subjected these weapons to 11 generations of bidirectional selection and found a correlated response in pupal survival but not in larval survival or adult longevity in the male. That is, selecting for male mandibles negatively impacted survival during the production of mandibles. There is no correlated response in the life-history traits of the female. © 2011 The Authors. Journal of Evolutionary Biology © 2011 European Society For Evolutionary Biology.

    DOI: 10.1111/j.1420-9101.2011.02303.x

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  • Male attractiveness, fertility and susceptibility to oxidative stress are influenced by inbreeding in Drosophila simulans

    K. Okada, J. D. Blount, M. D. Sharma, R. R. Snook, D. J. Hosken

    Journal of Evolutionary Biology   24 ( 2 )   363 - 371   2011年2月

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    掲載種別:研究論文(学術雑誌)  

    Inbreeding frequently leads to inbreeding depression, a reduction in the trait values of inbred individuals. Inbreeding depression has been documented in sexually selected characters in several taxa, and while there is correlational evidence that male fertility is especially susceptible to inbreeding depression, there have been few direct experimental examinations of this. Here, we assessed inbreeding depression in male fertility and a range of other male fitness correlates in Drosophila simulans. We found that male fertility and attractiveness were especially susceptible to inbreeding depression. Additionally, levels of testicular oxidative stress were significantly elevated in inbred males, although sperm viability did not differ between inbred and outbred males. Copulation duration, induction of oviposition, and the proportion of eggs hatching did not differ for females mated to inbred or outbred males. Nevertheless, our results clearly show that key male fitness components are impaired by inbreeding and provide evidence that aspects of male fertility are especially susceptible to inbreeding depression. © 2010 The Authors. Journal of Evolutionry Biology © 2010 European Society For Evolutionary Biology.

    DOI: 10.1111/j.1420-9101.2010.02170.x

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  • Intralocus sexual conflict unresolved by sex-limited trait expression

    Tomohiro Harano, Kensuke Okada, Satoshi Nakayama, Takahisa Miyatake, David J. Hosken

    Current Biology   20 ( 22 )   2036 - 2039   2010年11月

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    掲載種別:研究論文(学術雑誌)  

    Sexually antagonistic selection generates intralocus sexual conflict, an evolutionary tug-of-war between males and females over optimal trait values [1-4]. Although the potential for this conflict is universal, the evolutionary importance of intralocus conflict is controversial because conflicts are typically thought to be resolvable through the evolution of sex-specific trait development [1-8]. However, whether sex-specific trait expression always resolves intralocus conflict has not been established. We assessed this with beetle populations subjected to bidirectional selection on an exaggerated sexually selected trait, the mandible. Mandibles are only ever developed in males for use in male-male combat, and larger mandibles increase male fitness (fighting [9, 10] and mating success, as we show here). We find that females from populations selected for larger male mandibles have lower fitness, whereas females in small-mandible populations have highest fitness, even though females never develop exaggerated mandibles. This is because mandible development changes genetically correlated characters, resulting in a negative intersexual fitness correlation across these populations, which is the unmistakable signature of intralocus sexual conflict [1]. Our results show that sex-limited trait development need not resolve intralocus sexual conflict, because traits are rarely, if ever, genetically independent of other characters [11]. Hence, intralocus conflict resolution is not as easy as currently thought. © 2010 Elsevier Ltd All rights reserved.

    DOI: 10.1016/j.cub.2010.10.023

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  • Plasticity of size and allometry in multiple sexually selected traits in an armed beetle Gnatocerus cornutus

    Kensuke Okada, Takahisa Miyatake

    Evolutionary Ecology   24 ( 6 )   1339 - 1351   2010年11月

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    掲載種別:研究論文(学術雑誌)  

    Male-male competition frequently results in the evolution of sexually selected traits used as weapons and ornaments. The expression of these traits often depends on male condition, i. e., condition dependence. Although males often have multiple sexually selected traits, to date many studies have focused on the morphological analysis of one sexual trait whilst ignoring the others. We here report phenotypic plasticity for multiple sexual traits, by manipulating larval diet quality and density, in the broad-horned flour beetle Gnatocerus cornutus. The male beetles possess enlarged mandibles, developed genae and a pair of small horns, but females lack these completely. Larval density significantly affected overall body size but not relative investment in each sexual trait. In contrast, diet quality had no effect on body size but had a significant effect on relative investment in the mandibles and genae. These results indicate that the allometric intercepts of the mandible and genae alter in response to diet quality, i.e., allometric plasticity. However, diet quality had no effect on the growth of the horn. Thus, multiple sexual traits exhibited differences in plasticity as a result of larval nutrient condition in G. cornutus males. © 2010 Springer Science+Business Media B.V.

    DOI: 10.1007/s10682-010-9370-9

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  • Ejaculatory strategies associated with experience of losing

    Kensuke Okada, Takashi Yamane, Takahisa Miyatake

    Biology Letters   6 ( 5 )   593 - 596   2010年10月

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    掲載種別:研究論文(学術雑誌)  

    Modulation of behaviours as a result of fighting experience has been observed in many animals and can influence pre-copulatory sexual selection. This study investigated how fighting experience affects ejaculatory strategies. In male flour beetles, Gnatocerus cornutus, experience of losing a fight decreases a male's aggressiveness for up to 4 days. We found that males losing a fight show increased ejaculatory investment, but there was no ejaculatory modulation owing to winning. However, the increase in ejaculate investment following a loss was no longer observed after 5 days. These results indicate that males adjust their investment in sperm competition according to their experience, and that fighting experience can significantly influence pre-and post-copulatory reproductive tactics. This journal is © 2010 The Royal Society.

    DOI: 10.1098/rsbl.2010.0225

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  • Dispersal and ejaculatory strategies associated with exaggeration of weapon in an armed beetle

    Takashi Yamane, K. Okada, Satoshi Nakayama, Takahisa Miyatake

    Proceedings of the Royal Society B: Biological Sciences   277 ( 1688 )   1705 - 1710   2010年6月

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    掲載種別:研究論文(国際会議プロシーディングス)  

    Weapons used in male fighting can be costly to males and are often reported to trade off with other characters such as wings or spermatogenic investment. This study investigated whether increased investment into weapons can generate evolutionary changes in mating strategy for armed males. Male flour beetles, Gnatocerus cornutus, have enlarged mandibles that are used in male-male competition. We subjected these weapons to 12 generations of bidirectional selection and found trade-offs between weapons and two other male characters: wing and testis size. In addition, probably as a consequence of the observed changes in investment, dispersal ability and ejaculatory volume differ significantly between the lines. This indicates that the exaggeration of a weapon can be associated with dispersal and ejaculatory strategies. Thus, altered investment into weapons can lead to correlated changes in life-history traits. © 2010 The Royal Society.

    DOI: 10.1098/rspb.2009.2017

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  • Sperm Competition: Discrimination Isn't Always Bad

    Kensuke Okada, David J. Hosken

    Current Biology   20 ( 10 )   2010年5月

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    Observing sperm in competition has been limited by our ability to discriminate between males' sperm. Recent work has overcome this obstacle, while another study reports on seminal fluid with very specific spermicidal activity, suggesting discrimination is easy for some. © 2010 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.cub.2010.03.052

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  • On the optimal duration of memory of losing a conflict - a mathematical model approach

    Toru Sasakia, Kensuke Okada, Tsuyoshi Kajiwara, Takahisa Miyatake

    Journal of Biological Dynamics   4 ( 3 )   270 - 281   2010年5月

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    掲載種別:研究論文(学術雑誌)  

    In male broad-horned flour beetles, Gnatocerus cornutus, losers of conflicts avoid fighting at subsequent encounters. The loser effect lasts for 4 days. It is considered that the memory of losing remains for 4 days. The duration of the memory is expected to affect the fitness, and the duration, 4 days, is expected to be optimal.We consider the fitness of a mutant in an homogeneous population to obtain the optimal duration. Here we carry out simulations using an individual-based model. The results suggest that the trade-off of getting mating chances and avoiding damage can cause the optimal duration of the memory, and that the decay in time of the female population is an important factor. © 2010 Taylor & Francis.

    DOI: 10.1080/17513750903161036

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  • Effect of losing on male fights of broad-horned flour beetle, Gnatocerus cornutus

    Kensuke Okada, Takahisa Miyatake

    Behavioral Ecology and Sociobiology   64 ( 3 )   361 - 369   2010年1月

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    掲載種別:研究論文(学術雑誌)  

    Experience-dependent tactics of males trying to gain access to females were examined in the beetle Gnatocerus cornutus, which engages in male-male fighting for mates. In male fights, subsequent behavior is modified by winning and losing experiences. Males, therefore, may choose between several behavioral tactics to obtain a mate, based on his previous fighting experience. In G. cornutus, we examined for how long aggressive behaviors were modified by experiences of winning or losing, i. e., the duration of the prior experience effect. Losing decreased a male's frequency of fighting for 4days, and few defeated males fought any male regardless of the opponent's size. By the fifth day, this effect disappeared. No modulation of male behavior due to winning was observed. Furthermore, the experience of losing not only decreased a male's aggressiveness but also switched the male behavior from fighting to dispersal from the fight site to another site. In future, it is necessary to clarify why the optimal term of the losing experience is 4days in this beetle. © Springer-Verlag 2009.

    DOI: 10.1007/s00265-009-0852-0

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  • Genetic correlations between weapons, body shape and fighting behaviour in the horned beetle Gnatocerus cornutus

    Kensuke Okada, Takahisa Miyatake

    Animal Behaviour   77 ( 5 )   1057 - 1065   2009年5月

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    掲載種別:研究論文(学術雑誌)  

    Male fighting frequently results in the evolution of traits used as weapons. Additionally, males with well-developed weapons typically differ behaviourally and morphologically from weaponless males. However, the genetic basis to these phenotypic correlations has not been investigated. The broad-horned flour beetle, Gnatocerus cornutus, is a species in which males engage in fights using their enlarged mandibles. We conducted bidirectional selection on beetle mandible length to investigate the correlated responses in male behaviour and body shape. Mandible size diverged significantly after 10 generations of selection. We also found that the microevolutionary enlargement of mandibles affected male morphology and behaviour. Compensatory or supportive traits of the mandibles (head, prothorax, genae and forelegs) also became enlarged, but eye area, antenna, head horn and elytra length were all reduced. These correlated responses in morphology may be the result of developmental integration of these traits and mandibles, but the reduction in size of some traits could also be caused by trade-offs generated by resource competition between characters. In any case, the enlargement of the weapon (mandibles) altered male body shape into a suitable form for fighting. Fighting endurance also evolved as a correlated response to selection on mandible size, with lines selected for larger mandibles able to fight for longer. It therefore appears that morphology and fighting are genetically correlated with each other. © 2009 The Association for the Study of Animal Behaviour.

    DOI: 10.1016/j.anbehav.2009.01.008

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  • Fighting, dispersing, and sneaking: Body-size dependent mating tactics by male Librodor japonicus beetles

    Kensuke Okada, Takahisa Miyatake, Yuta Nomura, Kazuma Kuroda

    Ecological Entomology   33 ( 2 )   269 - 275   2008年4月

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    掲載種別:研究論文(学術雑誌)  

    1. Scaling relations between weapons and body size depart from linearity in many male beetles. In many previous studies, these males have been divided into major and minor males with a switch point, that is male dimorphism. Major and minor males adopt strikingly different reproductive tactics. 2. We found three size-dependent behaviours, i.e. fighting, dispersing, and sneaking, however, among Librodor japonicus males with dimorphic mandibles. We statistically classified males into large, medium, and small (L-, M-, and S-males) sizes and then compared the dispersal of males from a foraging site, behaviours to gain access to females, and sizes of mandibles, wings, and testes. 3. M-males dispersed earlier than L- and S-males from a territory in a field, but no difference in the frequency of dispersal was observed between L- and S-males. Observations of male-male interactions in the laboratory showed that L-males frequently fought with other males in a fighting arena, while S-males often showed sneaking behaviour without fighting. 4. On the basis of the morphological analysis, we concluded that S-males invested their available resources more in sperm (= testes), M-males more in wings, and L-males more in mandibles in L. japonicus. 5. Even though a morphological male dimorphism was detected, it might be possible to classify the males of the armed beetles into more than two behavioural tactics if we examine their behaviours. © 2008 The Authors.

    DOI: 10.1111/j.1365-2311.2007.00965.x

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  • Negative relationship between ambient temperature and death-feigning intensity in adult Callosobruchus maculatus and Callosobruchus chinensis

    Takahisa Miyatake, Kensuke Okada, Tomohiro Harano

    Physiological Entomology   33 ( 1 )   83 - 88   2008年3月

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    掲載種別:研究論文(学術雑誌)  

    Although the effects of temperature on insect behaviours are studied frequently, few studies report on the relationship between temperature and anti-predator behaviours. A negative relationship between ambient temperature and the intensity of death-feigning is found in adults of two seed beetle species, Callosobruchus maculatus (F.) and C. chinensis (L.) (Coleoptera: Bruchidae). Two traits representing the intensity of immobility, the frequency and the duration of death-feigning, are measured at different temperatures. Almost all adults feign death at 15 °C, but the frequency of death-feigning decreases at higher temperatures in C. maculatus, whereas all C. chinensis adults show this behaviour at 15 and 20 °C and almost all show it at 25 °C, but the frequency of death-feigning decreases at 30 and 35 °C. The difference between the two species might be due to the specific strain of each species used in the experiment. The duration of death-feigning is correlated negatively with the increase in ambient temperature in both species. The frequency at which adults feigned death is higher in females than in males in both species, but the duration of death-feigning is higher in females than in males only in C. maculatus. The relationships between temperature and death-feigning behaviours are discussed from physiological and ecological viewpoints. © 2008 The Authors.

    DOI: 10.1111/j.1365-3032.2007.00607.x

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  • Pleiotropic antipredator strategies, fleeing and feigning death, correlated with dopamine levels in Tribolium castaneum

    Takahisa Miyatake, Ken Tabuchi, Ken Sasaki, Kensuke Okada, Kohji Katayama, Seiichi Moriya

    Animal Behaviour   75 ( 1 )   113 - 121   2008年1月

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    掲載種別:研究論文(学術雑誌)  

    A prey animal has the alternative of fleeing or feigning death to survive when it encounters predators. We found that fleeing by an artificial threat, locomotion and feigning death are pleiotropically correlated with a genetic factor related to a biogenic amine in the red flour beetle, Tribolium castaneum. Walking distance of adults was significantly lower in strains artificially selected for longer (L strains) than shorter duration (S strains) of death-feigning. Crosses showed that S-strain adults were dominant in the frequency and duration of death-feigning and locomotor activity compared to those of L strains, suggesting that death-feigning and activity have the same genetic basis. S-strain adults fled, but L-strain adults feigned death, when they encounter artificial threat. Not only adults that were directly selected for the duration of death-feigning, but also the larvae of L strains frequently showed tonic immobility, when they were dropped onto the ground: the larvae of S strains showed this behaviour less often. This suggests that chemical modulators of behaviour present in these insects before and after metamorphosis control both general locomotor activity and death-feigning. Brain levels of the candidate neuromodulator dopamine were, in fact, found to be significantly higher in S strains compared to L strains in the two selection replications. Thus, we suggest that two alternative behaviours related to antipredator strategies, fleeing or feigning death, are associated with the pleiotropic effects of a neuroactive substance in T. castaneum. © 2007 The Association for the Study of Animal Behaviour.

    DOI: 10.1016/j.anbehav.2007.04.019

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  • Relations between allometry, male-male interactions and dispersal in a sap beetle, Librodor japonicus

    Kensuke Okada, Yuta Nomura, Takahisa Miyatake

    Animal Behaviour   74 ( 4 )   749 - 755   2007年10月

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    掲載種別:研究論文(学術雑誌)  

    Status-dependent tactics of males trying to gain access to females were examined in relation to morphology, male-male interactions and dispersal in a sap beetle, Librodor japonicus. Males of this species have sexually dimorphic enlarged mandibles which they use in fights for mates on a sap site. Morphological analyses revealed a switchpoint at which the linear slopes of mandible and hindwing width to body length increased and decreased, respectively. Larger males frequently fought with other males in an experimental arena, whereas smaller males often showed sneaking behaviour without fighting. Mark-release-recapture experiments showed a size-dependent difference in dispersal ability of males in the field. The longest dispersal distance was seen in intermediate-sized males, and the shortest dispersal distances were observed in the largest and smallest males. In females, no relation was found between body size and dispersal distance. The largest males thus remain on sap sites and fight with other males, the smallest males also remain on sap sites and try to sneak access to females, and intermediate-sized males move among sap sites and settle on one without a larger male. The results suggest a nondichotomous difference in optimal behavioural tactics of males even though male dimorphism has been detected in armed beetles. © 2007 The Association for the Study of Animal Behaviour.

    DOI: 10.1016/j.anbehav.2006.09.020

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  • Ownership-dependent mating tactics of minor males of the beetle Librodor japonicus (Nitidulidae) with intra-sexual dimorphism of mandibles

    Kensuke Okada, Takahisa Miyatake

    Journal of Ethology   25 ( 3 )   255 - 261   2007年9月

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    掲載種別:研究論文(学術雑誌)  

    Intra-sexual dimorphism is found in the weapons of many male beetles. Different behavioral tactics to access females between major and minor males, which adopt fighting and alternative tactics, respectively, are thought to maintain the male dimorphism. In these species major males have enlarged weapons that they use in fights with rival males. Minor males also have small weapons in some of these species, and it is unclear why these males possess weapons. We examined the hypothesis that minor males might adopt a fighting tactic when their status was relatively high in comparison with that of other males (e.g., ownership of a territory). We observed the behavioral tactics of major and minor males of the beetle Librodor japonicus, whose males have a dimorphism of their mandibles. Major males fought for resources, whereas minor males adopted two status-dependent tactics, fighting and sneaking, to access females, depending on their ownership of a sap site. We suggest that ownership status-dependent mating tactics in minor males may maintain the intra-sexual dimorphism in this beetle. © 2006 Japan Ethological Society and Springer.

    DOI: 10.1007/s10164-006-0021-0

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  • Librodor japonicus (Coleoptera: Nitidulidae): Life history, effect of temperature on development, and seasonal abundance

    Kensuke Okada, Takahisa Miyatake

    Applied Entomology and Zoology   42 ( 3 )   411 - 417   2007年

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    掲載種別:研究論文(学術雑誌)  

    Librodor japonicus (Motschulsky) is distributed throughout the satoyama forests in Japan, and inhabits the saps of oak trees all its life. Although the beetle is a potential indicator of bio-resource abundance in the satoyama forests, the life history traits and seasonal abundance have not been studied. In this study, first, the seasonal abundance of L. japonicus was investigated using banana bait traps in Okayama City in 2002. Two peaks of abundance were found: a large peak from April to June and a small peak from August to September. The beetles oviposited on banana slices, and a successful artificial rearing method was established using only banana slices and leaf mold. The effect of temperature on the survival rate, adult size and developmental period was examined at different temperatures. The survival rate and the adult size tended to be greater at 25°C than at other temperatures. The thermal thresholds and thermal constants calculated from egg to adult development were 5.6 and 5.9°C and 1,010.9 and 1,022.0 degree-days for females and males, respectively. On the basis of these developmental parameters and the seasonal abundance of L. japonicus, the number of generations per year in Okayama, Japan, was estimated to be one.

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  • Intra-sexual dimorphism in male mandibles and male aggressive behavior in the broad-horned flour beetle Gnatocerus cornutus (Coleoptera: Tenebrionidae)

    Kensuke Okada, Akihiro Miyanoshita, Takahisa Miyatake

    Journal of Insect Behavior   19 ( 4 )   457 - 467   2006年7月

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    掲載種別:研究論文(学術雑誌)  

    In the stored-product beetle, the broad-horned flour beetle, Gnatocerus cornutus (Fabricius), all males possess enlarged mandibles, widened gena, and a pair of small horns on the vertex, but females lack these completely. Observations of male-male interactions of G. cornutus showed that larger individuals won male-male fights, and that the mandibles were used as weapons. Morphological analysis based on the non-linearity test of Eberhard and Gutierrez's model (1991) showed that intra-sexual dimorphism in males was only found in the mandibles used in male-male combat, but not in the gena and horns. This beetle can be an ideal model for evolutionary studies of exaggerated weapons for male combat, because rearing successive generations and observing male fighting are easy. © 2006 Springer Science+Business Media, LLC.

    DOI: 10.1007/s10905-006-9038-z

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  • Sexual dimorphism in mandibles and male aggressive behavior in the presence and absence of females in the beetle Librodor japonicus (Coleoptera: Nitidulidae)

    Kensuke Okada, Takahisa Miyatake

    Annals of the Entomological Society of America   97 ( 6 )   1342 - 1346   2004年11月

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    掲載種別:研究論文(学術雑誌)  

    Sexual dimorphism was found in the mandibles and other supportive structures used in male-male combat over females in Librodor japonicus. Observation of the behavior of male-male interactions of L. japonicus elucidated the influence of contestant size and resource ownership status on the outcome of male-male fighting. Interactions escalated in the presence of females, indicating the influence of resource value on the intensity of male fighting. At escalated fighting, the outcome of combat was influenced by size and ownership status. This study is the first on sexual dimorphism and male fighting in the Nitidulidae. © 2004 Entomological Society of America.

    DOI: 10.1603/0013-8746(2004)097[1342:SDIMAM]2.0.CO;2

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担当授業科目

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