Size-related inbreeding preference and competitiveness in male Pelvicachromis taeniatus (Cichlidae)

Sexual selection is an important force in the evolution of body size. Both intersexual selection, that is, preference for large individuals, and intrasexual selection, that is, increased competitiveness of large individuals, are involved in this process. Furthermore, preferences based on body size of the choosing individual might also influence body size evolution. Here, we investigated male mate choice and competitiveness in relation to male body size in Pelvicachromis taeniatus, a size-dimorphic cichlid. In previous experiments, both sexes showed mating preferences for larger and genetically related individuals. First, we examined male inbreeding preferences based on olfactory cues. Males that highly varied in body size were given the choice between the odor of a familiar sister and the odor of an unfamiliar unrelated female that were presented in combination with a computer-animated image of a female P. taeniatus as a visual stimulus. Male preference for the odor of their sisters was correlated with male body size. Only larger males were choosy concerning related odors and preferred their sisters, whereas smaller males were unselective. Second, we showed that large males outcompete smaller males in contest over a breeding site. The extent of aggression was negatively correlated with the size difference between the 2 males. Variation in male choice may reflect an adaptive strategy: small, less competitive and less attractive males might avoid the risk of failing to mate at all by reducing choosiness. Consequently, only large competitive males should obtain the benefits of choice, which may further contribute to the selective advantages of large body size. Copyright 2011, Oxford University Press.