Patterns and processes of speciation in North American chorus frogs (Pseudacris)

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2007

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During speciation, populations become spatially separated from each other by biotic or abiotic factors, and this leads to genetic divergence and reproductive isolation. Here, I study the process of speciation and the patterns resulting from this process in the chorus frogs (Pseudacris). I first lay the foundation for this work by constructing phylogenies based on molecular data. I then address broad-scale questions regarding the abiotic factors thought to drive speciation. I examine evolution of reproductive signals within a phylogenetic context, and finally, I address fine-scale questions regarding the completion of reproductive isolation in contact zones between recently-evolved species. In chapter 1, I estimate the phylogenetic relationships across the genus Pseudacris. I find that several species of unclear status (regilla, cadaverina, crucifer, ocularis) belong to this genus, and that P. ocularis is the sister species of P. crucifer. In chapter 2, I examine the phylogeography of a clade within Pseudacris, the trilling chorus frogs. I find support for at least nine species and delineate their geographic distributions. In chapter 3, I test geological and climatic hypotheses proposed to drive speciation in North American flora and fauna. By estimating divergence times in the trilling chorus frogs and correlating these divergences with timing of geologic events, I find that marine inundation of the Mississippi Embayment may have caused speciation in this group. Additionally, I find that climatic events led to reduced genetic variation rather than divergence within species. In chapter 4, I study the evolution of acoustic signals of all species of Pseudacris. Using a comparative method approach, I find that physiologybased call variables are more evolutionarily labile than morphology-based call variables. In addition, I find that sympatric signals are more different than allopatric signals, suggesting that these frogs have partitioned the acoustic niche. In chapter 5, I examine evolution of reproductive isolation between two chorus frog species in sympatry. I find that male signals show a repeated pattern of divergence in sympatry, and that different axes of the signal diverge in different populations, suggesting that heterospecific overlap may lead to reproductive isolation among conspecific populations. I also find that female preferences have evolved in sympatry, suggesting that divergence in the contact zone is due to reinforcement.

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