Coevolution of male courtship and sexual conflict characters in mosquitofish

Coerced copulations cause sexual conflict: they enhance male fitness at a potential cost to female fitness. In contrast, male display allows female mate choice and stimulates cooperation, and so is thought to be an alternative to coercion. Here, we investigate the evolutionary relationship between coercion and display in Gambusia, a genus of poeciliid fish. We used a novel Markov chain method to quantify the transition rate from a male display to a copulatory thrust (the display-to-thrust [DT] rate), which we use to measure the importance of male display to copulation. We assess the potential for male coercion and the female response to coercion based on morphology. We found positive relationships between DT rate and 2 morphologies that are indicative of coercion: male gonopodium shape and the male morphological mating advantage (the ratio of gonopodium shape to female papilla size scores). We suggest that male display can cause the evolution of traits involved in sexually antagonistic coevolution, or conversely that display can evolve as a byproduct of sexual antagonism.