Assessment of Spatial and Temporal Variation in Relative Frequencies of Alternative Reproductive Tactics in Blue Ridge Two-Lined Salamander (Eurycea cf. wilderae)

Alternative reproductive tactics (ARTs) are discrete intrasexual differences in reproductive behavior within individuals in natural populations. While some ARTs are purely behavioral, they are often accompanied by morphological and physiological divergence. In the southern Appalachian Mountains, populations of the Blue Ridge Two-Lined Salamander (Eurycea cf. wilderae) exhibit a unique case of ARTs, with males occurring in two genetically determined morphs: “searching” and “guarding” males. During their reproductive season, searching males engage in terrestrial courtship and develop elongated cirri to detect and locate mates, whereas guarding males remain near aquatic nesting sites and develop hypertrophied jaw musculature used in aggressive mate-guarding behavior. Unlike most cases of ARTs in amphibians, the ARTs found in E. cf. wilderae have a genetic proximate cause controlled by a Y-linked genetic polymorphism. This provides a unique study system for evolutionary biology. This thesis examined the possible mechanisms that have maintained this polymorphism by investigation of the spatial and temporal variation in ART frequencies. First, we explored the spatial distribution of genotype frequencies across a heterogeneous environment; specifically, we compared 5 small and 5 large stream habitats. After we genotyped ~1,150 salamanders, we found searching males at significantly higher frequencies in small streams than in large streams; this suggests stream size and differentiation of habitats may play a role in the persistence of these ARTs. Next, we initiated data collection for a long-term study focused on temporal variation. We analyzed ART frequencies from the same small stream across three years in the context of humidity and precipitation. Our results indicated that ART frequencies did not differ significantly across years, but provide a framework for understanding the potential influence of humidity and precipitation on ART frequencies. By integrating spatial and temporal analyses, this thesis provides new insights into the ecological and evolutionary forces shaping ART maintenance, offering a broader understanding of how genetic polymorphisms persist in natural populations.