Phylogeography, population genetic structure, and reproductive biology of antelope ground squirrels

Thesis (Ph. D.)--University of Washington, 2006.The genetic structure of populations over a wide geographic area should reflect the demographic and evolutionary processes that have shaped a species across its range. Similarly, variation in physiological traits should reflect the degree to which a species can either tolerate, through behavioral or phenotypic plasticity, or adapt to local environments across its range. I examined the distribution and diversity of both neutral genetic variation and reproductive physiology within the Antelope ground squirrel, Ammospermophilus leucurus .In my first and second chapters I examine the population genetic structure of Antelope ground squirrels across the complex of North American deserts from the Great Basin of Oregon to the cape region of the Baja California peninsula. I estimated phylogenies of both the mitochondrial cytochrome-b gene and control region gene to infer population structure and history. The gene trees revealed genetic uniformity in a monophyletic northern Glade, and a more diverse, monophyletic southern clade. The distribution and diversity of mutations plus the minimal geographic structure of the northern clade suggest a rapid northward expansion of the population that must have followed a northward desert habitat shift associated with the most recent Quaternary climate warming and glacial retreat. The more variable distribution of pairwise differences and higher haplotype diversity of the southern suggests a longer, more stable history associated with a southern peninsular refugium.In my third chapter, I discuss how the geographic distribution of genetic diversity and reproductive traits within A. leucurus compares to an existing gradient of environmental conditions. Gestation and lactation of an individual female require about three months, and individuals breed only once per year. The overall breeding season of populations are relatively short in Oregon and California, but extends over nearly half a year in the southern Baja California peninsula. Litter size decreases significantly from north to south. A major shift in environmental seasonality, biotic diversity, and ecosystem composition are associated with the longer breeding season and lower litter size at the southern geographic extreme of A. leucurus