Meeting Abstract
Natural and sexual selection may interact in shaping phenotypic traits. In some species of the fish family Poeciliidae, males obtain copulations by harassing females and thrusting their intromittent organ (gonopodium) towards the female genital pore. Hence, males must swim fast and skillfully towards females. We used Poeciliopsis infans as model system and asked if particular sizes and shapes of males are better in gaining copulations. In addition, we asked if the same sizes and shapes have higher survival probabilities, presumably through fast swimming that may help in avoiding predators. We estimated male survival in the wild (natural selection), measured swimming velocity and quantified the number of successful copulations in the laboratory (sexual selection), and used geometric morphometric techniques to measure body size and shape. Our results indicate that larger and streamlined males have higher survival probabilities. We also observed faster swimming velocity in more elongated males. In addition, we found evidence of disruptive selection in terms of mating success. The largest males with deepest bodies as well as the smallest males with thinnest bodies obtained more successful copulations. We provide evidence of a complex interaction between natural and sexual selection shaping the size and shape of these males.
