Masked Expression of Life- History Traits in a Highly Variable Environment

Diff ering lifehistory strategies may act as a constraint on reproductive expression that ultimately limits the ability of individual species to respond to changes in the magnitude or frequency of environmental variation, and potentially underlies the variation oft en inherent in phenotypic and evolved responses to anthropogenic change. Alternatively, if there are environmental cues that predict reproductive potential, diff erential expression of lifehistory strategies may represent diff erences in the adaptive capacity to optimize current reproductive value given variation in environmental conditions. We compared several aspects of walleye Sander vitreus spawning ecology at two reservoirs that diff er in environmental variability (i.e., annual waterlevel fl uctuation) to identify the capacity of phenotypic expression and the corresponding association with age. Despite signifi cant diff erences in female body and liver masses between reservoirs that diff er in environmental variability, we found no diff erence in reproductive investment measured by egg size and fecundity. Walleye in a highly variable environment appear to exhibit reproductive traits more typical of a shortlived lifehistory strategy, which may be resultant from the interaction of environmental and anthropogenic pressures. Th is fi nding emphasizes the need to identify the degree to which lifehistory expression represents physiological constraints versus ecological optimization, particularly as anthropogenic change continues to alter environmental conditions.