Reproductive strategies of Gammarus lacustris (Crustacea : Amphipoda) along an elevation gradient

1. The number of eggs, their size, mass and development time, and the starv ation time of newly hatched young, was examined in four populations of Gamm arus lacustris along an elevation gradient from prairie to alpine lakes (73 0 m to > 2300 m above sea level). Water temperature and ice-free season dec reased with increasing altitude. 2. Females in the alpine lake produced fewer but larger and heavier eggs th an females in the prairie lake. Eggs produced by females in montane and sub alpine lakes were intermediate in size, mass and number. Within populations , egg size was not related to the number of eggs or female size. 3. The development time of eggs declined with an increase in incubation tem perature. At all incubation temperatures, large eggs had a longer incubatio n time than small eggs. All eggs incubated at 4 degrees C failed to produce young. Young from large eggs were larger in size than young from small egg s. 4. The starvation time of newly hatched young increased with decreasing tem perature. However, slopes of regressions relating starvation time to temper ature differed among populations. At 4 degrees C young from large eggs surv ived longer than young from small eggs. 5. The high phenotypic plasticity in reproductive traits contributes to the success of G. lacustris in a wide range of aquatic habitats. It is predict ed that in response to climate-induced warming, populations in currently co ld montane and alpine lakes would shift their reproduction to produce more eggs of smaller size. However, the accurate prediction of the fate of popul ations between ecoregions will require knowledge of the extent to which the se traits are under genetic control.