LATITUDINAL DIFFERENCES IN SOMATIC ENERGY-STORAGE - ADAPTIVE RESPONSES TO SEASONALITY IN AN ESTUARINE FISH (ATHERINIDAE, MENIDIA-MENIDIA)

This study focuses on the seasonal accumulation and depletion of somat ic energy in the Atlantic silverside (Menidia menidia), an annual estu arine fish. Previous research revealed that northern silversides are s ubject to strong size-dependent winter mortality, while southern fish suffer no appreciable winter mortality. To examine whether there was g eographic differentiation in allocation strategies, we compared tempor al patterns of energy storage and utilization among three populations along this gradient in seasonality. The comparative design used monthl y or biweekly samples of fish collected in the wild, as well as sample s of fish from each population reared in a common environment, where g enetic differences can be clarified. Somatic energy stores were quanti fied via gravimetric analysis of neutral storage lipids and lean tissu e. Analysis revealed that small individuals maintained relatively low levels of lipid reserves, which may account for their lower survival i n winter. Wild fish in the north rapidly accumulated large somatic res erves, which were depleted over the winter and then increased again du ring the subsequent spring breeding season. In wild southern fish, rel atively small reserves accumulated slowly until breeding commenced in the spring. The common-environment comparison of somatic storage patte rns revealed a genetic basis for among-population differences in reser ve accumulation rates, but no differences in the amount of reserves st ored. We conclude that the overwinter depletion of somatic reserves ha s a significant selective impact on energy accumulation and allocation strategies in seasonal environments.