In the interest of studying another species (other than newts) that mates multiply, stores sperm, and has a longer breeding season I began studying livebearing fish (Poeciliidae). I began by examining male and female mate preference in sailfin mollies, Poecilia latipinna. I have subsequently moved on to more evolutionarily based questions for my postdoctoral research. For my NSF postdoctoral research with Professor Mike Ryan, I examined the hypothesis of reproductive character displacement using a unisexual-bisexual complex of mollies (Poeciliidae). Amazon mollies, Poecilia formosa, are unisexual hybrids that reproduce by gynogenesis by eliciting sperm transfer from related male sailfin mollies, P. latipinna, but inheritance is strictly maternal. I compared the mating preference of males from six sympatric populations with males from five allopatric populations. Males from the sympatric populations showed a significantly greter strength of preference for conspecific females than did mals from allopatric populations. Thus, I found strong evidence for displacement of male mate choice in sympatry. Additionally, allozyme variation has been examined to estimate gene flow and its relationship with the spread of the male discrimination trait from areas of sympatry into areas of allopatry and to evaluate the potential effect of local selection pressures on adaptation. This work is currently in progress. Sailfin molly courtship Male sailfin molly checking out an Amazon molly