Meeting Abstract
Most studies examining adaptive phenotypic plasticity focus on one environmental gradient; however, natural populations face combinations of multiple selective agents. Here we tested whether phenotypic responses of female least killifish depended on historical environmental conditions: one of high predation risk/low conspecific density and one of low predation risk/high conspecific density. We predicted that populations would have evolved a diminished response to the dominant selective agent to maintain fitness in these environments. First, we exposed female fish to either a caged warmouth sunfish for 30 min. or no predator. After 30 additional min. all fish were snap frozen and analyzed for whole-body corticosterone (CORT). In another experiment, we housed females from each population in 114 l tanks at two densities (3 or 15), and measured reproductive output, growth, and whole-body CORT at the end of the experiment. As predicted, fish with historical exposure to high predation threat exhibited a reduced CORT response to the predator than those from the population with high exposure. In the density experiment, only females from the low-density population had a dramatic reduction of offspring in the crowded conditions relative to those at low density; yet there were no differences in body weight or CORT between densities in fish from either population. Although females from historically high-density conditions maintained fitness, the reduction in fecundity in females from the low-density population was not mediated by changes in CORT secretion. We are currently determining whether the difference in the reproductive response to density between these two populations is associated with changes in reproductive hormones or gene expression profiles in the ovary/placenta.
