A female fish that today doesn't need males to clone itself copulates with other species' males to stimulate embryonic development. Those males do that probably because the interactions of a sexual male and the female are observed by conspecific females and make that male more attractive

Male mate choice in Livebearing fishes: an overview. Ingo Schlupp. Current Zoology, zoy028, https://doi.org/10.1093/cz/zoy028

Abstract: Although the majority of studies on mate choice focus on female mate choice, there is growing recognition of the role of male mate choice, too. Male mate choice is tightly linked to two other phenomena, female competition for males, and ornamentation in females. In the current paper I review the existing literature on this in a group of fishes, Poeciliidae. In this group male mate choice appears to be based on differences in female quality, especially female size, which is a proxy for fecundity. Some males also have to choose between heterospecific and conspecific females in the unusual mating system of the Amazon molly. In this case, they typically show a preference for conspecific females. While male mate choice is relatively well documented for this family, female ornamentation and female competition are not.

Keywords: fecundity, sexual selection, female choice, Poecilia, Xiphophorus, Gambusia, guppy, binary choice test, preference function, female size

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Amazon mollies are an all-female, clonal species of fish of hybrid origin (Hubbs & Hubbs 1932, Schlupp & Riesch 2011). The maternal ancestor is the Atlantic molly P. mexicana and the paternal ancestor is the sailfin molly P. latipinna. The single, original hybridization apparently took place about 100.000 generations ago in an area near present-day Tampico [...]. Amazon mollies reproduce by gynogenesis, where sperm simply serves as stimulus for embryonic development, but is typically not incorporated into the offspring (Schlupp 2005) [...] The Amazon molly uses at least three species as sperm donors [...]

More importantly, this situation can be used to make very clear predictions relative to male mate choice. For males the fitness return for mating with Amazon mollies is very low. Even if the cost of mating is low or moderate, males should evolve to prefer conspecific females, or lower their cost by investing less into heterospecific copulations. Via mate copying, a process of using social information in mate choice (Varela et al. 2018, Witte et al. 2015), males gain an indirect fitness benefit offsetting some of the cost of heterospecific matings: the interactions of a sexual male and an Amazon molly are observed by conspecific females and make that male more attractive to conspecific females. Interestingly, males have also been shown to copy the mate choice of other males (Bierbach et al. 2011, Schlupp & Ryan 1997).


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