THE SONG OF THE SWORD-TAIL: UNRAVELING THE GENETIC BASIS OF COURTSHIP SONG VARIATION IN THE LAUPALA CRICKET SPECIES RADIATION
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Behavioral evolution is one of the most potent mechanisms driving reproductive isolation between diverging populations of animals. Premating courtship behaviors are particularly important, as evidenced by their association with many of the most rapid species radiations currently known. Investigating the genetic bases of these complex behavioral phenotypes is integral to our understanding of the speciation process at a molecular level. The importance of gene expression in controlling phenotypic variation has been known for decades, but only since the recent sequencing revolution has its role in speciation been truly appreciated. Theoretical modeling and empirical studies alike have concluded that gene expression changes likely precede changes in protein-coding genes and thus play an outsized role in the early stages of divergence, especially when it comes to modulating complex courtship phenotypes. We took advantage of the Laupala cricket species radiation to investigate the role of gene expression plays in early lineage divergence and reproductive isolation. We examined the genetic architecture of pulse rate using an F2 hybrid mapping population derived from the fast singing L. kohalensis and the slow singing L. paranigra and found evidence supporting the hypothesis that variation in this behavior is driven by many loci of small effect. Annotation of these regions using RNA sequencing data suggest they may be enriched for genes predicted to affect rhythmic behavior. Assessing differential gene expression between the same parental species and F2 hybrids led us to discover significantly more misexpression in hybrids than predicted as well as identify a set of compelling candidate genes modulating pulse rate variation between L. kohalensis and L. paranigra. We then found evidence of significant parallel gene expression evolution when comparing gene expression profiles of L. kohalensis and L. paranigra to an independent species pair with matching pulse rate phenotypes, the fast singing L. neospisa and slow singing L. spisa. This allowed for identification of candidate genes potentially involved in modulating pulse rate variation throughout the radiation. Taken together, the work presented here increases our understanding of the role gene expression plays in rapid species radiations and thus our understanding of key mechanisms underlying the speciation process.
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Reed, Robert
Bass, Andrew