Meeting Abstract
Behavioral isolation typically evolves as a by-product of divergence in mating preferences between geographically isolated populations, but it also can be strengthened upon secondary contact by reinforcement. Reinforcement occurs when hybrid offspring have reduced fitness, leading to stronger prezygotic isolation in sympatry than in allopatry. Behavioral isolation appears to be important in the speciation process for darter fishes (Percidae: Etheostoma); however, some allopatric pairs of darter species lack preference for conspecifics, sometimes even preferring heterospecific phenotypes, suggesting that divergence in geographic isolation alone may be insufficient to maintain species boundaries. Therefore, we tested the hypothesis that reinforcement strengthens behavioral isolation between the partially sympatric darter species Etheostoma zonale and E. barrenense. Previous work has found that both sexes of E. zonale significantly prefer conspecifics over sympatric E. barrenense. In the current study, we collected E. zonale from populations allopatric with respect to E. barrenense and measured male and female preferences for con- and heterospecific stimuli, predicting that strength of preference would be greater in sympatry than in allopatry. We used a general linear model to test the effect of sex and sympatry on strength of conspecific preference. Results show that the interaction of sex and sympatry significantly predicts strength of preference in E. zonale; specifically, female strength of preference decreases with increased distance from sympatry, whereas male preferences were similar across all populations. Our results therefore suggest that reinforcement is shaping female preferences and that male preferences may be evolving earlier than females’ in allopatry.
