Male reproductive phenotype and coercive mating performance in the guppy Poecilia reticulata

In species with fixed alternative male mating tactics, differences between male phenotypes associated with each tactic are well understood. By contrast, in species with fully interchangeable male mating strategies, associations between male phenotypes and fitness when adopting different tactics have received much less attention. One such species is the Trinidad guppy Poecilia reticulata, where males perform high rates of coercive mating attempts (gonopodial thrusts, GTs hereafter) but also switch between GTs and courtship with great flexibility. Male phenotypes favored by females have been described in detail and consist of complex, nonlinear combinations of traits. Coercive tactics also contribute towards male fitness, but no study to date has provided a multivariate description of guppy phenotypes able to obtain fertilizations via GTs, despite evidence suggesting they should be different from phenotypes successful in cooperative mating scenarios. Here we observe male mating behavior in freely interacting mixed-sex groups and compute a GT performance variable based on the closest distance the male approaches the female before abandoning the thrust. We use multivariate selection techniques to relate GT performance to traits and combinations of traits known to contribute towards male fitness. Guppy males that perform best in GTs are small, bold, with large areas of iridescent coloration and fast-swimming sperm, as well as intermediate orange coloration and sperm count. This phenotype only partly confirms our expectation, as it comprises traits advantageous in cooperative mating scenarios. Our study highlights the importance of using multivariate approaches when investigating sexual selection in the context of coercive mating strategies.