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Flucutating sexual selection and the evolution of a courtship strategy
Han, C. S., Brooks, R. C., & Jablonski, P. G.
Fluctuating sexual selection caused by environmental heterogeneity can maintain variation in sexual signals. Sexual selection can also shape correlations among behavioral traits (behavioral syndromes) when certain behavioral combinations enjoy greater fitness than other combinations (i.e., under correlational sexual selection). Here, we tested the hypothesis that environmental heterogeneity in predation risk shapes the evolution of courtship tactics and behavioral syndromes of male water striders Gerris gracilicornis. Male G. gracilicornis use an intimidating form of courtship that depends on predation risk, and we predict that male courtship and related behavioral syndromes will be associated with the form of sexual selection under predation. We assayed 4 male behaviors: sex recognition sensitivity, exploration in a novel environment, intimidation, and boldness toward predators. We also estimated males’ reproductive success in both the absence and presence of a predator. We found no predation-risk induced differences in linear (i.e., directional) sexual selection. Both treatments experienced directional selection favoring more intimidating courtship by males. Nonlinear sexual selection, however, varied with predation risk. Additionally, we found that sexual selection was not related to the behavioral syndrome structure. Overall, we demonstrate that sexual selection varies with predation risk in ways that might favor the spread of a novel courtship strategy (intimidating courtship) and the maintenance of alternative mating tactics in G. gracilicornis.