Mating preferences of Amazon mollies (Poecilia formosa) in multi-host populations

Gynogenesis is a peculiar mode of clonal reproduction in which eggs need to be pseudo-fertilized by sperm, but the male genes are not passed on to the offspring. One mating system in which gynogenesis is found involves a unisexual hybrid, the Amazon molly (Poecilia formosa), which typically uses males of its two parental species as sperm donors. Most gynogenetic lineages do not sexually parasitize males that were not involved in their hybrid origin and although some gynogens have the ability to utilize males from additional species, they rarely occur in sympatry with more than one sperm host. A few populations of the Amazon molly, however, do occur syntopically with more than one host species, raising the question of whether specific preferences have evolved in P. formosa and whether Amazon mollies can now act like Red Queens, driving the evolution of discrimination abilities in the host species. Near Ciudad Mante, Mexico, the critically endangered Tamesí molly (P. latipunctata) occurs in exclusive sympatry with Amazon mollies and one of P. formosa’s parental species, the Atlantic molly (P. mexicana). In this study we tested the initial and post-exposure preference of allopatric and sympatric P. formosa (with regards to P. latipunctata) between P. latipunctata and P. mexicana males. We predicted that P. formosa should favour P. mexicana because this is a parental species to P. formosa and the asexual shares half of the P. mexicana genome. Contrary to our predictions, we found no significant differences between preference scores in allopatric and sympatric populations of P. formosa in initial or postexposure trials. Our findings may indicate that males of both species are perceived as equally effective in triggering embryogenesis by P. formosa. This study, along with limited previous work in the system, calls to attention the exploration of the adaptive ability of gynogenetic species relationships, and their implications for the long-term persistence of not only asexual lineages, but also the parasitized sexual species.