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UBC Theses and Dissertations

Understanding parapatric range limits in the long-toed salamander, Ambystoma macrodactylum Lee-Yaw, Julie Anne


Understanding geographic range limits is an outstanding challenge in evolutionary ecology. My goal was to characterize and evaluate factors contributing to parapatric borders in the long-toed salamander (Ambystoma macrodactylum). Using amplified fragment length polymorphism and mitochondrial data, I tested whether currently-recognized subspecies of long-toed salamander are distinct evolutionary units. My results demonstrate that the long-toed salamander consists of at least four divergent lineages. Discordance between these lineages and current subspecies designations, as well as evidence for a cryptic lineage, emphasize the need to reevaluate existing taxonomy prior to conducting studies of species’ range limits. To further understand the distribution of diversity in this system, I explored the role of climate in shaping lineage boundaries. Using spatial data and ecological niche modeling, I asked whether the boundaries between lineages reflect the limits of their respective climatic niches. My results suggest that the different long-toed salamander lineages are ecologically similar and that suitable climatic space for each lineage exists well-beyond shared borders. Although some contact zones coincide with areas where the average climatic suitability for both lineages is low, sites that are highly suitable for each lineage can be found within these regions in all cases. Thus climatic barriers alone are unlikely driving range limits in this system. I next examined the role of hybridization in shaping range limits. I characterized fine-scale patterns of genetic structure in a contact zone between two long-toed salamander lineages. To determine whether there is evidence of hybrid dysfunction, I assayed adult feeding performance in the laboratory. I observed reduced feeding performance in populations coinciding with the extent of mitochondrial introgression but not in populations that are more admixed. These results may be relevant for understanding the limits of introgression for some genes, but not all. Thus the study of range limits in the context of hybrid zones may require consideration of factors governing differential rates of introgression across the genome. This dissertation demonstrates the use of multiple lines of investigation to narrow down the most relevant hypotheses for parapatric range limits and highlights the potential for several factors to ultimately be shaping species’ range limits.

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