Association preferences of unisexual Amazon mollies (Poecilia formosa): differential response to swords based on sex of the bisexual parental species

Most females exhibit preferences for certain males and females based on mating and social decisions. Unisexual females that reproduce by gynogenesis are also expected to express association preferences, which may have been inherited from parental species, or may have evolved in response to selection pressures associated with their unisexual mating system. The unisexual, gynogenetic Amazon molly (Poecilia formosa) is a hybrid of the Atlantic molly (P. mexicana) and sailfin molly (P. latipinna). Although none of these three species have sword tails, the two parental species differ in preference for swords on conspecifics. We further examined the variation in pre-existing bias within this species complex by testing Amazon molly preference to associate with male and female sailfin mollies with artificially attached swords. Amazon mollies significantly avoided females with colored swords, but were indiscriminate towards swords on males. Thus, this hybrid species shares its lack of preference for swords on males with female Atlantic mollies and females from one population of sailfin mollies. Avoidance of females with swords by Amazon mollies is unique in this species complex. We discuss the implications and functions of association preferences expressed by Amazon mollies and propose hypotheses for the differential response towards swords based on sex.