Identifying female phenotypes that promote behavioral isolation in a sexually dimorphic species of fish (Etheostoma zonale)

In sexually dimorphic species characterized by exaggerated male ornamentation, behavioral isolation is often attributed to female preferences for conspecific male signals. Yet, in a number of sexually dimorphic species, male mate choice also results in behavioral isolation. In many of these cases, the female traits that mediate species boundaries are unclear. Females in sexually dimorphic species typically lack many of the elaborate traits that are present in males and that are often diagnostic of species. In a diverse and largely sexually dimorphic group of fishes called darters (Percidae: Etheostoma), male mate choice contributes to behavioral isolation between a number of species; however, it is not clear which female traits males prefer. In the current study, we identified the dominant female pattern for two sympatric species, Etheostoma zonale and E. barrenense, using pattern energy analysis, and we used discriminate function analysis to identify which aspects of female patterning can reliably classify species. We then tested the role of female features in male mate choice for E. zonale, by measuring male preference for computer animations displaying the identified (species-specific) conspecific features as well as the dominant male pattern that is preferred by females. We found that the region above the lateral line is important in mediating male mate preferences, with males spending significantly more time with animations exhibiting conspecific female patterning in this region than with animations exhibiting heterospecific female patterning. Our results suggest that the aspects of female phenotypes that are the target of male mate choice are different from the male phenotypes that characterize species. This research highlights the importance of using objective measures in the study of behavioral isolation via male mate choice.