Publishing type：Research paper (scientific journal)   Publisher：Public Library of Science (PLoS)  

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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Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Trophallaxis plays a major role in the sharing of food in colonies of many social insects, and two modes of this are known: stomodeal (oral) and proctodeal (abdominal) trophallaxis. In social Hymenoptera, only a small proportion of colony members perform the task of food collection, and oral trophallaxis is predominant in their social sharing of food. Typically, foragers distribute liquid food stored in their crop to nestmates via oral trophallaxis. Similar to bees, some ants (Formicidae) forage for liquid food from plant secretions (nectars) and insect exudates (honeydew). While regurgitation is common in ants, it has been documented in only two species of the Ponerinae. Here, we report the ability of Diacamma sp. from Japan to perform trophallaxis. After thirsty ants had been paired with ants provided with colored water, the abdomens of both groups of ants were dissected. The digestive organ was colored red in half of the receivers. In addition, we observed mouth-to-mouth interactions in the laboratory, not “social bucket” behavior (i.e., exchange of liquid held between mandibles). Our results suggest that Diacamma sp. can exchange liquid by true oral trophallaxis and shed new light on social organization via liquid exchange.

DOI： 10.1007/s10164-019-00602-9

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Other Link： http://link.springer.com/article/10.1007/s10164-019-00602-9/fulltext.html

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

The success of social insects is often attributed to the specialized morphologies and behaviours of workers. One of the most elaborate specializations in ant species is the workers’ plugging behaviour, in which their uniquely shaped heads are used for nest defence. These species generally nest in tree cavities. Without morphologically specialized workers (major workers) plugging the nest entrance, nests are easily attacked and replaced by conspecific and heterospecific cavity-dwelling ants and other predators. Therefore, major workers are expected to defend the nest at all times. However, empirical evidence on the social time investment for nest defence is still lacking. Here, we investigated how major workers of Colobopsis nipponicus achieve nest defence (plugging behaviour) in terms of their work schedule. Our results showed that the nests had more major workers than entrances. The observation of artificial plastic nests over 6 days in the laboratory revealed that the nest entrance was guarded almost continuously by multiple major workers. The entrance-guarding schedule was not equally divided among major workers, and there were no clear shift patterns in the timing of changeovers. We highlight the importance of investigating the time investment of workers to fully understand the defence strategies of this morphologically specialized caste.

DOI： 10.1111/eth.12877

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1111/eth.12877

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract: Social insect colonies are highly organized systems, where communication among nestmates (i.e., social interactions) has a pivotal function for colonial organization. In order to further the understanding of social organization, the chronobiological system of social insect species, particularly their circadian rhythm, has recently attracted much attention. However, gaps still remain in our understanding of how individual active/rest rhythms are governed in various social contexts. In this study, we investigate the effects of worker-worker interactions on circadian activity rhythms, using the monomorphic ant, Diacamma sp. Continuous tracking of solitary ants elucidated circadian activity rhythms, both in young and old workers (< 30 days and > 70 days after eclosion, respectively). The color tag–based automatic tracking of multiple workers revealed that young-old interactions reduced circadian rhythmic activities in both young and old workers, whereas young workers retained active/rest rhythms under young-young worker interactions. Together with the analyses of worker-worker interaction frequencies, we conclude that interactions between workers in different age groups (i.e., workers with different tasks) function as different cues to alter worker active/rest patterns. We discuss the potential roles of worker-worker interactions on the chronobiological organization of the ant society. Significance statement: In social animals, how individual behavioral rhythms are governed by social interactions is a fundamental question towards the mechanistic understanding of complex biological systems. Using an image-based tracking system, we composed artificial ant worker groups consisting of different functions (i.e., young nurses and old foragers) and investigated whether the age composition and the resulting interactions had an effect on the active/rest rhythms of individual workers, and of the whole group. In solitary conditions, both young and old workers showed circadian activity; however, when grouped with workers from different age groups, both young and old workers turned to show weak circadian rhythmicity or around-the-clock activity. Our results suggest that even simple social cues (i.e., frequency of contact with young and old workers) could alter worker activity patterns. To our knowledge, this is the first evidence showing that specific worker-worker interaction induces weakly rhythmic and/or arrhythmic states.

DOI： 10.1007/s00265-019-2641-8

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Other Link： http://link.springer.com/article/10.1007/s00265-019-2641-8/fulltext.html

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：The Royal Society  

In group-living animals, social interactions influence various traits including circadian activity. Maternal care, in particular, can have a strong effect on the circadian activity of parents or nurses across taxa. In social insects, nest-mates are known to have diverse activity rhythms; however, what kind of social environment is crucial in shaping an individual's rhythm is largely unknown. Here, we show that the focal brood types being taken care of (i.e. egg, larva and pupa) have significant effects on individual activity/rest rhythm, using the monomorphic ant
<italic>Diacamma</italic>
(putative species
<italic>indicum</italic>
). When isolated from a colony, nurses exhibited a clear circadian rhythm. However, when paired with eggs or larvae, they exhibited around-the-clock activity with no apparent rhythm. In contrast, a clear activity rhythm emerged when nurses were paired with a pupa, requiring little care. Such brood-type-specific changes in circadian activity are considered to arise from the difference in caretaking demands. Our finding may contribute to the understanding of the organization of a colony in the context of behavioural variability under different microenvironments.

DOI： 10.1098/rsbl.2016.0743

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Other Link： https://royalsocietypublishing.org/doi/full-xml/10.1098/rsbl.2016.0743

Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.7210/jrsj.35.455

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