Asexuality shapes traits in a hybrid fish.

Animal morphology is influenced by several factors, including gonadal development and gametogenesis. Although their effects are well documented in male/female differentiation, much less is known about same-sex effects, such as those caused by their mode of reproduction. Here, using geometric morphometric analyses, we compare two groups of all-female triploid hybrid fish Chrosomus eos × eos-neogaeus, that differ only by their sexual and asexual reproductive strategies. We demonstrate that morphological differences arise from factors inherently associated with their mode of reproduction, with results replicated in two distinct lineages and in natural and common garden environments. Such differences provide additional insight about the costs and benefits of both reproductive strategies, which have mostly been of a demographic, population genetic, or genetic nature. In particular, these findings have important implications for the ecology of asexual organisms and contribute to the study of sex evolution by adding complexity to the paradox of sex theory.