P2-223 Saturday, Jan. 5 15:30 - 17:30 Genital evolution in livebearing fishes of caves and toxic springs MCNEMEE, RE*; GREENWAY, R; TOBLER, M; Kansas State University email@example.com
Populations of Poecilia mexicana, a live-bearing fish common in freshwater streams in Southern Mexico, have adapted to life in toxic sulfide streams in and outside of caves. Previous studies have shown that these populations have evolved morphological, physiological, and behavioral adaptations to extreme environments, resulting in ecological speciation. Reproductive isolation between populations in differing habitat types is facilitated by natural and sexual selection against migrants between habitats. However, selection against migrants cannot solely explain the low levels of observed gene flow. We predict genital divergence between populations may contribute to reproductive isolation. The question remains, however, whether and how the genitalia of males (gonopodial tip) and females (urogenital aperture) differ among populations inhabiting contrasting environments. Particularly, the cave populations may have evolved differences in genital traits associated with a sensory role in sexual selection in the absence of light. We quantified genital variation in four populations of Poecilia mexicana (sulfide surface, non-sulfide surface, sulfide cave, and non-sulfide cave) with ongoing speciation to test if male and female genitalia diverge in a correlated fashion. We found that there is divergence in genitalia across populations in different habitat types. We also document evidence that male and female genitalia have coevolved within populations. The basic requirements for mechanical isolation are consequently fulfilled in this system, and experimental studies are now needed to understand the functional significance of genital variation.