Genetic and Geographic Boundaries in the Spring Peeper (Psuedacris crucifer) with Insights into Mito-Nuclear Discordance, Reticulation, Niche Divergence and Isolation
The reduction of gene flow is often associated with divergence and initial stages of speciation. In the absence of gene flow, sister lineages should diverge genetically from one another in a roughly clock-like fashion even without divergent ecological pressures. However, the biotic and abiotic forces which underpin divergence in a species’ ecology are seldom static in space or time. Organismal adaptability and the impermanence of ecological barriers can result in the opportunity for renewed gene flow over the history of a species. Under the biological species concept this is when species boundaries are tested. Such variable patterns of genetic exchange can leave complicated phylogenetic signals. I investigated the spring peeper (Pseudacris crucifer), a frog that is well suited to studying the role of gene flow in speciation due to its massive geographic range and multiple parapatric lineages. I first explored the range-wide patterns of intraspecific genetic and call diversity. I then focused on one distinctive inter-lineage contact zone to quantify the patterns of gene flow and variation in call and morphological traits across it. Finally I modeled the contribution of climate, elevation and reproductive interference to the distribution of both lineages. My work revealed patterns of phylogenetic and geographic discordance between mitochondrial and nuclear DNA, driven by the apparent widespread introgression of nuclear DNA. I also observed narrow, generally coincident clines in call and genetic traits suggesting a tension zone at one contact zone that coincides with a distinct altitudinal and climatic ecotone. The patterns I observed in P. crucifer imply a complex relationship between environment, allopatry, divergence, and gene flow. Populations within one region (westernmost part of the species range) have diverged from populations across the remainder of species range, where gene flow appears to be homogenizing differences in zones of contact. Pseudacris crucifer provides a compelling example of the importance of range-wide genetic studies, the complicated evolutionary histories of species that occur in areas impacted by glaciation, and the consequences of gene flow on diversification to the level of incipient species.
URI for this recordhttp://hdl.handle.net/1974/28087
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