Geographical Variations in Body Size, Brood Size and Egg Size of a Freshwater Shrimp, Palaemon paucidens DE HAAN, with Some Discussionon Brood Habit

Abstract

The variations in body size, egg size and brood size of berried females among populations have not been known in Palaemon paucidens. These were examined among 28 local populations from various inland waters over its range of geographical distribution. Body size differs among the populations. Egg size is almost constant regardless of body size within a population, but differs among the populations, and the largest from Lake Akan is about seven times as large as the smallest from Lake Biwa. Brood size increases with body size, however, relative brood size is almost similar within a population. Among the populations, mean brood size and mean relative brood size vary, but fall within a limited range, except for the mean relative brood size in Lake Biwa, which is exceptionally large. Relative brood weight is almost similar in a population, as well as mean relative brood weight among the populations. Thus, mean relative brood size is almost inversely proportional to mean egg size. A geographical trend is noticeable in the variations of these two values (i. e., larger mean egg size and smaller mean relative brood size in colder waters), except for the populations in Lake Biwa and two rivers of Boso. The small body size of the population in Lake Biwa can be related to its life history, in which a longer period is spent in colder conditions, and the high relative brood size can be regarded as its adaptive strategy of allocation.