Absence of female preference and the origin of a unisexual species, the Amazon molly (Poecilia formosa)

Abstract

The role of hybridization as a formative process in evolution has received much attention in the past few decades. A particularly fascinating outcome of hybrid speciation is the formation of asexual hybrid species. This is the case in the Amazon molly (Poecilia formosa). It is of hybrid origin and had a P. mexicana female as mother and a P. latipinna male as father. This implies that at the beginning of the existence of Amazon mollies, a heterospecific mating must have occurred, indicating a breakdown of any potential prezygotic isolation between parental species. We studied the female mate choice behavior with present day P. mexicana and P. latipinna from several populations using standard binary choice tests. Overall, our results show that in extant P. mexicana and P. latipinna no female choice for conspecific males was detectable. Consequently, heterospecific matings are possible, even likely, and not hindered by any apparent behavioral prezygotic isolation. If female preferences in these species were comparable around the time the Amazon molly originated as a hybrid species ca. 100.000 years ago, matings leading to hybrids would be very likely. Furthermore, for the first time we tested the mating preferences of F1 hybrid females and found that they also have no discernable mating preferences, potentially leading to F2 individuals and/or backcrosses.