Rex Meade Strange: Evolution of sexual dimorphisms in spottail darters (teleostei: percidae): fitness sets, phylogenetics, and a test of the egg-mimic hypothesis
I investigated the dynamics between reproductive ecology and morphological phenotypes among spottail darters by developing a fitness set model. Spottail darters exhibit two types of sexual dimorphism, and both presumably related to male resource- defense polygyny. My model considers male phenotypes as conflicting signals in mate choice behavior. Large male size is an honest signal in my model, by which large males obtain and defend better nests. Female choice for large males increases female fitness. Males of some species develop large knobs supported by rays of the second dorsal fin. Fin knobs are hypothesized to act as egg-mimics used to attract receptive females, if females selectively deposit their eggs in nests that already contain eggs despite the size of the male guarding that nest. Egg-mimicry is a false signal in my model. Female choice for males exhibiting egg-mimics may decrease female fitness when nest sites are limiting. Medium size males with small knobs are at a disadvantage in my model, as they lack the large size required to acquire nest sites and effective egg-mimics. Phylogenetic relationship among spottail darters is consistent with the model: Large egg-mimics evolve twice, and are always associated with a reduction in male size. Species in which egg-mimicry is maintained occur in habitats in which nest sites are not limiting. Further, large male size has re-evolved in one species restricted to nest-poor habitats with a simultaneous reduction in egg- mimics.