Life history variation of a freshwater amphipod, Jesogammarus paucisetulosus.

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Interpopulational differences in life history features were studied for a stream-inhabiting amphipod, <I>Jesogammarus paucisetulosus</I>. In a population of Mt. Tsukuba, reproduction occurred from winter to late spring, and almost all adults died by August. The smallest body length was 6.5 mm for mature males and 5.0 mm for mature females in early winter. They grew during the breeding season. The rate of ovigerous females was high from February to May (>78%). The rate of paired females was also high in that period, and usually became higher as moulting (oviposition) drew nearer in a reproductive cycle. A rearing experiment showed that clutch intervals were 50, 34 and 20 days at 6, 11 and 17°C, respectively. From the field and experimental data, the number of clutches per female was estimated to be about three. On the other hand, reproduction occurred throughout the year in Mito City, probably because of a little seasonal variation of water temperature. The population always consisted of individuals of different ages, and the life history was semi- annual. The mean body length of breeding individuals was smaller than that in the population of Mt. Tsukuba for both males and females. The smallest size of mature individuals varied seasonally, and the seasonal pattern differed between the sexes. The rate of ovigerous and paired females varied seasonally, and decreased in summer.
日本陸水学会の論文