The evolution of the placenta causes a conflict-driven shift in sexual selection in the livebearing fish family Poeciliidae
Friday seminar by Bart Pollux
The evolution of the placenta from a non-placental lecithotrophic ancestor causes a shift of maternal investment from pre- to post-fertilization, creating a venue for parent-offspring conflicts during pregnancy. Theory predicts that the rise of these conflicts should drive a shift from a reliance on pre-copulatory female mate choice to polyandry in conjunction with post-zygotic mechanisms of sexual selection. This hypothesis has not yet been empirically tested. Here we apply comparative methods to examine potential conflict-driven shifts in sexual selection associated with the evolution of the placenta in the livebearing fish family Poeciliidae. We exploit a unique quality of this family, which is to have evolved placentas at least eight times while retaining close relatives that lack placentas. We show that the evolution of post-zygotic maternal provisioning by means of a placenta is associated with the evolutionary loss of bright coloration, courtship behavior and exaggerated ornamental display traits in males. Furthermore, we found that males evolve smaller bodies and longer genitalia, which facilitates sneak or coercive mating and, hence, circumvents female choice. Our results demonstrate that the emergence of prenatal conflict during the evolution of the placenta results in strong directional sexual selection towards a suite of specific phenotypic and behavioral male traits that limit female mate choice prior to copulation.
1) Experimental Zoology Group, Wageningen University (the Netherlands) and
2) Department of Biology, University of California Riverside (USA)