CHAN, L. M.; Cornell University: Genetic structure in an abundant toad with a rare metamorph

Genetic population structure and diversity are important indicators of connectivity, persistence, and evolutionary potential. While dispersal capacity and geographic barriers certainly contribute to the differentiation of populations, species-specific aspects of life history, mating system, and ecology may also play a role. In the southwestern deserts of the United States, the Great Plains toad (Bufo cognatus) is a highly seasonal breeder dependent on summer monsoons that fill ephemeral pools and cue the emergence of individuals from the ground. For one to three nights following heavy rains, adults aggregate in high densities at suitable ponds to mate and lay eggs. Due to mating system characteristics and life history traits, only a small proportion of males are successful at obtaining mates and fathering clutches. In addition, because the intensity, timing, and duration of rains is highly variable, reproductive efforts are often lost as many sites dry too rapidly for tadpoles to metamorphose and leave the pond. Thus, species traits in combination with extreme environmental stochasticity create the potential for a high degree of genetic structure at relatively fine spatial and temporal scales. I use microsatellite markers to assess population structure within the San Simon Valley and two adjacent valleys in Arizona and New Mexico. Understanding the level and scale of differentiation serves as a launching point for future studies of the relative contribution of specific parameters to the origin and persistence of genetic diversity within species.