MATE CHOICE IN THE SAILFIN MOLLY, POECILIA LATIPINNA.

We examined both female and male mate choice in the sailfín molly, Poecilia latipinna. Female mollies preferred larger males over smaller ones when comparing males from their own populations. Although the expression of this preference depends on a female's receptive state, the level of female preference does not appear to be associated with any other attribute of the female or of the males. When presented with males of the same size from different populations, females preferred native over foreign males in some but not all population combinations. These results cannot be explained by a bias for higher size-specific rates of courtship displays that is shared by all females. Males preferred larger over smaller females; larger males exhibited stronger preferences, and preference for the larger female also increased as the disparity in size between the two object females increased. We found no evidence that males preferred native over foreign females when encountered singly or in size-matched combinations. These results indicate that discrimination among populations arises because females exercise divergent directional preferences for size-specific trait values that are associated with differences among males in these values. This result implies an active role for sexual selection in contributing to the maintenance of the behavioral or morphological distinctions among males observed within and among populations.