Phylogeography, Ecogeographic Variation, And Evolutionary History Of The Collared Pika (Ochotona Collaris)

Abstract

In this dissertation I address the evolutionary history, ecogeographic variation, and phylogeography (single species and comparative) of collared pikas (Ochotona collaris). Pikas are small (ca. 150 g) lagomorphs (order Lagomorpha: rabbits, hares, and pikas) found in alpine habitats throughout much of the Holarctic. Only two of the 30 extant pika species occur in the New World. The northern of the two species, O. collaris is separated 800 km north of the American pika (O. princeps). In the first chapter, I employ recently developed molecular analytical techniques to examine when the two North American species diverged. This chapter sets the evolutionary context for the subsequent diversification within O. collaris. In the second chapter, I take a finer-scale view of morphological and ecogeographic variation in the collared pika. I examined morphological variation along a latitudinal gradient and over the past half century. While the length of the growing season appears to best explain latitudinal trends, temporal changes in body size are better explained by interrelated pressures resulting from heat stress and loss of snow cover. In the third chapter, I assess the major phylogeographic patterns within O. collaris and compare the observed levels of diversity within O. collaris to those in other alpine-adapted small mammal species. There are two main phylogroups in O. collaris, which appear to be in contact in Wrangell-St. Elias National Park and Preserve. The within-phylogroup and within-species genetic diversity in O. collaris is lower than that observed in other pikas. In the fourth chapter, I contrast the two O. collaris phylogroups with similar patterns in four co-distributed arctic-alpine small mammals in a comparative phylogeographic context. Although there are differences in the amount of diversity and extent of each phylogroup, simultaneous divergence into similarly distributed intraspecific phylogroups in all five species is supported. Four of the species, including O. collaris, show evidence of Pleistocene population expansion followed by recent demographic decline. Throughout the dissertation, I focus on the role of location (latitude) and time frame in geographically structuring genetic and morphological variation.