DISSERTATION RESEARCH: Examining the role of reinforcement in driving genomic divergence between and within species in darters

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The study of how species arise has been revolutionized by new technologies that allow researchers to get large amounts of genomic information from different species quickly. This technology has been used to identify areas of the genome that differ between populations occurring in different environments, and which may be important in preventing closely-related species from forming hybrids. This project uses similar methods to compare populations that differ in whether they co-exist with a close relative with which they can hybridize. The project focuses on orangethroat darter fish. The project will identify genome areas associated with a preference to mate with one's own species, and test whether the same genetic changes happen in all closely-related species that coexist, or whether unique genetic changes occur each time. Data obtained from this study will provide critical insight into how differences in biological communities can drive species diversity. This project will provide valuable research opportunities and teaching materials for undergraduate students. Furthermore, the results of this research will be used to educate community members about the biology of local native fish species. Reinforcement plays a critical role in finalizing the process of speciation after secondary contact by increasing prezygotic isolation between taxa that produce unfit hybrids. As reinforcement directly selects for divergence in mating traits in sympatric populations, it can also incidentally lead to behavioral isolation among populations within species (i.e., cascade reinforcement). The objective of this project is to develop genomic tools to examine how reinforcement affects genome-wide divergence between and within species in two groups of darters (the orangethroat darter clade Ceasia and the rainbow darter Etheostoma caeruleum). Previous studies have provided strong behavioral evidence that reinforcement is driving behavioral isolation between sympatric Ceasia and E. caeruleum, and subsequently causing cascade reinforcement and behavioral isolation between species within Ceasia. This research will examine genomic divergence between species experiencing reinforcement, and investigate whether this divergence between species may incidentally be causing genomic divergence among populations within species (or among recently diverged species). Specifically, Next-Generation Sequencing will be utilized to (1) identify any differences in chromosomal structure between Ceasia and E. caeruleum that may be contributing to postzygotic isolation and facilitating reinforcement, (2) identify loci responsible for postzygotic isolation between Ceasia and E. caeruleum by genotyping hybrid and backcross individuals, and (3) conduct genome scans that compare genetic differentiation between multiple populations of Ceasia that are sympatric and allopatric with respect to E. caeruleum, in order to identify highly differentiated outlier loci between sympatric and allopatric populations that are likely associated with prezygotic isolation.