DISSERTATION RESEARCH: Does Transgressive Segregation in Physiological Niche Explain the Rapid Spread of Invasive Genes into a Native Population

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Major rapid evolutionary changes are well known, but the underlying mechanisms and how these changes influence survival and reproduction are often unclear. This project will address the process of rapid evolutionary change by investigating whether the success and geographic spread of an introduced salamander species is the result of interbreeding with a native species. Although the introduction of non-native species is thought to lead to rapid evolution, it is still not understood how often this occurs, the factors involved, and whether this promotes the success and spread of the introduced species. Sometimes introduced species hybridize with native species and produce viable offspring that exhibit extreme trait values not present in either parental species. For example, offspring may be bigger than either parental species or have an increased tolerance to environmental stressors. Potentially, such hybrid offspring can outcompete the parental species or colonize new environments not occupied by either parental species. The production of extreme trait values due to interbreeding - transgressive segregation - is rare in viable offspring. However, when it occurs the offspring can interact with the environment in entirely new ways, leading to rapid evolutionary change. The researchers will study genetic mixing between an endangered native species, the California tiger salamander, and a closely related introduced species, the barred salamander, to test the hypothesis that transgressive segregation has led to extremely rapid evolution in the native species. Data will reveal how life history, physiology, and habitat combine to determine genetic pattern across a region where the two species overlap and hybridize. The project also includes the training of undergraduate and graduate students, educational programs targeting K-12 students, and workshops for conservation managers. Hybrids between Ambystoma tigrinum mavortium and A. californiense exhibit transgressive segregation with respect to body size and exhibit a broader thermal tolerance than natives. However, we still do not know whether transgressive segregation of ecologically important traits is a major factor affecting the extremely rapid spread of what are being labeled "superinvasive" genes into native populations. The researchers will measure and compare metabolic rates, rates of water loss, stress response to conspecific density, and thermal tolerance at multiple life stages in native, introduced, and hybrid tiger salamanders, the categories that matter for predicting spread on the real California landscape. Data on native and hybrid salamanders will be generated using a captive colony of salamanders of native and hybrid individuals. Parental, non-native salamanders will be collected from several wild populations within their native range and from an introduced population that is currently outside the zone of overlap with the native species. Information learned will then be used along with a novel population genetic simulation to generate robust mechanistic predictions of dispersal and persistence of native and nonnative genotypes within the real California landscape under current and potential future conditions.