Converging or diverging? Shape coevolution between a sperm-dependent asexual and its sexual hosts

Asexual species, despite lacking recombination, can evolve in response to environmental changes and influence the evolutionary trajectory of coexisting sexual species. Gynogenesis, where asexual females rely on sperm from males of a different species, offers a unique perspective on the eco-evolutionary dynamics between asexual females and their sexual hosts. The Amazon molly, Poecilia formosa, is a gynogenetic species that primarily uses sperm from two sympatric sexual species: the sailfin molly (P. latipinna) and the Atlantic molly (P. mexicana). To understand shape variation in an asexual species relative to their sexual hosts, we analysed shape variation among wild Amazon mollies and their sexual hosts. We tested three hypotheses: (i) Amazon mollies mimic their sexual hosts to enhance mating opportunities (sexual mimicry hypothesis); (ii) ecological interactions or male mate choice drive morphological divergence (character displacement hypothesis); and (iii) Amazon mollies exhibit random shape variation due to their asexual nature (null hypothesis). Our findings revealed significant shape variation in Amazon mollies, which differ from their sexual hosts in a host-specific manner (e.g. Amazon mollies with P. latipinna resemble P. mexicana and vice versa), supporting character displacement at the interspecific level in a sexual-asexual system.