Intrapopulation Variation in the Reroductive Characteristics of Two Populations of Ligia oceanica (Crustacea: Oniscidea)

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Abstract
(1) Reproductive females from two populations of Ligia oceanica (L.), an essentially semelparous species requiring at least 1 year to produce a brood, showed seasonal varibility in weight-specific fecundity and egg weight between two breeding groups. Small differences in reproductive effort between breeding groups were due to the relationship between body size and tissue energy content; a constant proportion of body weight was devoted to reproduction by individuals in both breeding groups. (2) A simple hierarchical additive model explained 97-99% of the variation in both fecundity and egg size, and identified the magnitude and direction of factors in a causal hierarchy affecting fecundity and egg size. Increased weight-specific reproductive allocation was devoted solely to increased fecundity, with no effect on egg size. A trade-off between fecundity and egg weight explained a large amount of the total variation in fecundity (13%) and egg size (22%). (3) As seasonal variation in egg-weight was related to the seasonal variation in total population assimilated energy (an index of available food), individuals may have been able to adjust egg size to match predictable changes in food supply. Flexibility in reproductive traits may present a sophisticated life-history strategy for individual woodlice.