Sex-specific life history patterns in bluegill (Lepomis macrochirus): interacting mechanisms influence individual body size
The ultimate body size that an individual fish achieves can be a function both of direct effects of growth or indirect effects associated with the timing of sexual maturation (and associated energetic tradeoffs). These alternatives are often invoked to explain variation in body size within and among fish populations, but have rarely been considered simultaneously. We assessed how resource availability and timing of maturation interact to influence individual body size of bluegill (Lepomis macrochirus). Resource availability (high and low food) and the social structure of the population (presence or absence of large, mature males) were varied in experimental ponds. Food ration affected growth (larger fish in the high food treatments) and the social structure of the population affected timing of maturation (early maturation of males in the absence of large males). Treatment effects, however, were sex-specific; males responded to the social structure of the population and females were more responsive to resource availability. We also found individuals that became sexually mature were smaller than those that remained immature, although results were sex-specific and resource dependent. For males, individuals that matured were smaller when resources were limited; mature and immature females showed no difference in body size regardless of food ration. We show that both resource availability and the processes that control timing of maturation interact in sex-specific ways to influence body size of bluegill. These results suggest that a more robust explanation for variable body size requires consideration of sex-specific interactions between ecological (food and growth) and evolutionary (timing of maturation) mechanisms.
KeywordsVariation Resource availability Social influence Body size
We are grateful for the assistance of T. Jaecks, B. Braetigam, E. Ozier, K. Schnake, and B. Davis for assistance with sampling and processing. Earlier drafts of this manuscript were improved by suggestions from Drs. R. Fischer, S. Robinson, R. Warner, N. Metcalfe, E. Marschall, the Aquatic Ecology Discussion Group at the Kaskaskia Biological Station, and an anonymous reviewer. Statistical advice was provided by the University of Illinois Statistical Consulting Service. Funding for this project was provided in part by the Federal Aid in Sportfish Restoration Act, Project F-128-R administered by the Illinois Department of Natural Resources (IDNR). We thank M. Conlin, L. Dunham, S. Stuewe, and S. Pallo for coordinating activities with the IDNR.
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