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MALE CONTRIBUTIONS TO REINFORCMENT AND SPECIATION IN DROSOPHILA**

Abstract

A recurring question in biology is where the boundary lies between one species and when it diverges into new, distinct lineages. The Drosophila subquinaria species complex is an example of speciation through isolation and secondary contact. During the Wisconsin glaciation D. subquinaria and Drosophilia recens were isolated on the west and east coast of northern America. During this isolation period D. recens became infected with Wolbachia. During secondary contact Wolbachia incompatibilities resulted in a strong postzygotic barrier to gene flow between populations. The reproductive barrier between populations was asymmetrical; in areas of sympatry, D. subquinaria suffers greater fitness reduction when mismating, causing D. subquinaria to have high levels of prezygotic mate discrimination. This reinforcement extends so far that D. subquinaria females discriminate against allopatric populations of D. subquinaria. Female mate discrimination has been well studied, however, the male role in reinforcement has yet to be explored. It remains unclear why there are greater levels of gene flow of D. recens nuclear genes into D. subquinaria populations, despite D. subquinaria being the species possessing mate discrimination. In our initial experiment we assessed intraspecific male aggression levels in D. subquinaria and D. recens sympatric populations and D. subquinaria allopatric populations. Using a Kruskall-Wallis test we found that D. recens males have significantly higher levels of within population aggression with a mean of 2.2857 (h=19.91, p< 0.001), compared to the D. subquinaria sympatric populations (0.7272 and 0.625). The current experiment will test interspecific male interaction when placed in direct contact following the same qualitative data previously compared for Drosophila aggression characteristics. If D. recens males continue their high aggression levels with both D. subquinaria populations, it will potentially explain why there are higher levels of gene flow from D. recens into D. subquinaria populations despite asymmetrical female discrimination. Any levels of aggression between allopatric and sympatric D. subquinaria populations may reflect early behavioral isolation and incipient speciation.

Acknowledgements

Piedmont University Natural Science Department

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