Use of microsatellite paternity analysis to determine male mating success in the western mosquitofish, Gambusia affinis

I tested the effects of male body size on male mating behavior and reproductive success in the western mosquitofish, Gambusia affinis. In two separate behavioral experiments (male-male competition and no-competition), I tested the predictions that (1) larger males out-compete smaller males for mates and (2) small males increase their number of mating attempts in the absence of a larger competitor. I estimated male mating success both indirectly (via behavioral experiments) and directly (using microsatellite DNA to assign parentage) and compared the two measures. Results from behavior experiments showed that, when in direct competition, large males were more aggressive and attempted more copulations than small males. In addition, paternity analyses illustrated that large males sired more offspring. I found no significant correlations between male body size (and other correlated traits) and mating success in a male-male competition study, suggesting that relative male size influences male mating behavior but absolute male size does not. When competition was removed, small males mated at equal rates to larger males. Finally, indirect estimates of male reproductive success explained about 67% of the variation in parentage by males, suggesting that indirect measures of mating are good predictors of actual male reproductive success in mosquitofish.