研究者詳細 - 秋山　貞

論文 - 秋山　貞

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Life history of Nippoleucon hinumensis (Crustacea: Cumacea: Leuconidae) in Seto Inland Sea of Japan. II. Non-diapausing subpopulation

T. Akiyama, Masamichi Yamamoto

Marine Ecology Progress Series 284 227 - 235 2004年12月

掲載種別：研究論文（学術雑誌）

The great majority of Nippoleucon hinumensis (Gamô) in the Seto Inland Sea of Japan enters a long-term summer diapause from May to November. We identified a minor subpopulation of N. hinumensis (0.7% of the total population) that became adults in a short period without diapause. Small-sized ovigerous females (15% shorter than the ordinary-sized ovigerous females) appeared from January to early February, a month earlier than the appearance of the ordinary-sized ovigerous females that produce diapausing offspring. These precociously ovigerous females released offspring from early February to early March. The offspring developed from 1st manca larvae to 2nd manca larvae, 1st juvenile stage and 2nd juveniles stage in that order, and in mid-April they reached the adult stage (5th instar) without diapause. In the non-diapausing subpopulation, sexual dimorphism was apparent from the 1st manca instar and the sex ratio (males:females) was 2 to 4:1. The molts, occurring at intervals of ca. 10 d, were not highly synchronous among individuals. The non-diapausing females mostly disappeared in April without producing offspring, but many non-diapausing males survived until the ordinary-sized ovigerous females started incubation of the second brood in late April. Possibly, the non-diapausing subpopulation is maintained through mating of non-diapausing males with ordinary-sized ovigerous females. The non-diapausing mode of life in N. hinumensis may represent the ancestral life mode before this species acquired a summer diapause mechanism.

DOI： 10.3354/meps284227

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Life history of Nippoleucon hinumensis (Crustacea: Cumacea: Leuconidae) in Seto Inland Sea of Japan. I. Summer diapause and molt cycle

T. Akiyama, Masamichi Yamamoto

Marine Ecology Progress Series 284 211 - 225 2004年12月

掲載種別：研究論文（学術雑誌）

The life history of the cumacean Nippoleucon hinumensis was investigated in the Seto Inland Sea of Japan from August 1998 to February 2002. The population produced 1 generation per year and recruitment of offspring occurred in April. The post-marsupial period consisted of 8 instars in males and 9 (plus generally 2 repeated instars) in females. Post-marsupial development up to the 4th instar (2nd juvenile stage) was characterized by periodic molting at intervals of 10 d, slow growth rate, and suppression of sexual dimorphism. Thereafter, the juveniles entered a long-term summer diapause from mid-May to early December, during which the ambient seawater temperature ranged from 15 to 28°C. Ninety-nine % of the population during the diapause were at the 2nd juvenile stage, and 1 % were at the 1st juvenile stage. In December, the cumaceans resumed growth, characterized by a fortnightly molt cycle, until the females began to incubate the first brood in late February. Each molting was highly synchronized among individuals and phased with the lunar cycles. After the end of the summer diapause, sexual dimorphism became apparent, with ovigerous females becoming about 1.2 times larger than adult males. After release of manca larvae in early April, most females incubated a second brood in late April, and then rapidly disappeared due to mortality probably caused by high water temperature. Clutch size was 57.9 ± 9.4 for the first brood and 42.4 ± 7.3 for the second.

DOI： 10.3354/meps284211

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Entrainment of the circatidal swimming activity rhythm in the cumacean Dimorphostylis asiatica (Crustacea) to 12.5-hour hydrostatic pressure cycles.

Tadashi Akiyama

Zoological science 21 ( 1 ) 29 - 38 2004年1月

記述言語：英語掲載種別：研究論文（学術雑誌）

The cumacean Dimorphostylis asiatica (Crustacea) exhibits a circatidal swimming activity rhythm. The animals were exposed to a 12.5 hr sinusoidal change of hydrostatic pressure of 0.3 atm amplitude in the laboratory. Under constant dark conditions, most of the specimens were entrained to a daily bimodal swimming activity rhythm by the hydrostatic pressure cycle. A small number of individuals exhibited a unimodal daily rhythm, with no apparent entraining from the administered cycles. A marked feature was a flexible phase relationship between the entrained daily bimodal rhythm and the hydrostatic pressure cycles: the swimming activity of most of the specimens occurred around the pressure-decreasing phase, but for a small number of individuals it coincided with the pressure-increasing phase. Such flexibility suggests a weak entraining effect of hydrostatic pressure on the circatidal rhythm of this species. When exposed to 24 hr light-dark cycles and a hydrostatic pressure cycle simultaneously, the specimens exhibited a rhythmic activity entrained by the hydrostatic pressure cycle during the dark period, which closely resembles the temporal activity pattern of this species in the field. The light cycles entrained the swimming activity via direct inhibition and induction of activity (i.e., masking). Under light-dark conditions, the specimens exhibited activity on the pressure-increasing phase more frequently compared with specimens kept in constant darkness.

DOI： 10.2108/0289-0003(2004)21[29:EOTCSA]2.0.CO;2

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Entrainment of the circatidal swimming activity rhythm in the cumecean Dimorphostylis asiatica (Crustacea) to 12.5-hour hydrostatic pressure cycles. 査読

Tadashi Akiyama

Zoological Science 21 29 - 38 2004年

Life history of Nippoleucon hinumensis (Crustacea: Cumacea) in Seto Inland Sea of Japan. I. Summer diapause and molt cycle. 査読

Tadashi Akiyama, Masamichi Yamamoto

Marine Ecology Progress Series 284 211 - 225 2004年

Life history of Nippoleucon hinumensis (Crustacea: Cumacea: Leuconidae) in Seto Inland Sea of Japan. II. Non-diapausing subpopulation.) 査読

Tadashi Akiyama, Masamichi Yamamoto

Marine Ecology Progress Series 284 227 - 235 2004年

Tidal adaptation of a circadian clock controlling a crustacean swimming behavior

Tadashi Akiyama

Zoological Science 14 ( 6 ) 901 - 906 1997年12月

掲載種別：研究論文（学術雑誌）

Cumacean Dimorphostylis asiatica exhibits an endogenous swimming rhythm, free-running period of which spontaneously changes from circa 12-hr to circa 24-hr in the laboratory. Administration of a 4-hr pulse of hydrostatic pressure stimulus and a 4-hr light pulse confirmed that the circa 12-hr rhythm is circatidal and the circa 24-hr rhythm circadian, with respect to the phase setting characteristics. The activity records provide evidence of a "splitting" phenomenon, which suggests that these two types of rhythms are governed by (an) identical pacemaker(s). This species appears to have acquired tidal synchrony by making use of flexibly coupled circadian pacemakers, accompanied by expansion of their subtidal habitat to shallow, tide-affected area.

DOI： 10.2108/zsj.14.901

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Circatidal swimming activity rhythm in a subtidal cumacean Dimorphostylis asiatica (Crustacea)

T. Akiyama

Marine Biology 123 ( 2 ) 251 - 255 1995年8月

掲載種別：研究論文（学術雑誌）

Dimorphostylis asiatica, a cumacean crustacea inhabiting the sublittoral line of the Seto Inland Sea, shows a rhythmic pattern of swimming activity coinciding with daily and tidal components in the field. This activity pattern was bimodal at first, i.e., circatidal activity coinciding with high tides at their habitat. The mean free-running period (i.e., bitidal interval) of this endogenous rhythm was 23.1 h at 10°C, which was significantly shorter than the environmental tidal cycle. In most cases (90% of the records) this bimodal activity became unimodal within 10 d. The unimodal period was 24 to 27.5 h, which is markedly longer than the preceding bimodal period. The bimodal pattern observed in the present study was not observed in the field. The difference between field and laboratory activity patterns can be explained in terms of direct response of the bimodal circatidal rhythm to the day-night cycle in the field. Field observations were made and laboratory experiments conducted between 1988 and 1992. © 1995 Springer-Verlag.

DOI： 10.1007/BF00353616

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The tidal rhythm of emergence, and the seasonal variation of this synchrony, in an intertidal midge

M. Saigusa, T. Akiyama

Biological Bulletin 188 ( 2 ) 166 - 178 1995年

The nocturnal emergence activity rhythm in the cumacean Dimorphostylis asiatica (Crustacea)

T. Akiyama, M. Yoshida

Biological Bulletin 179 ( 2 ) 178 - 182 1990年

掲載種別：研究論文（学術雑誌）

Dimorphostylis asiatica actively swims in the water at night. Males are positively phototaxic. Nearshore collections of males have demonstrated a clear rhythmic pattern, with emergence synchronized with both day-night and tidal cycles. While emergence was strongly synchronized with high tide during the winter and spring, tidal synchrony was scarcely detected in summer and autumn. -from Authors

DOI： 10.2307/1541766

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