Historical population genetics of temperate forest occupants in North and South America

The evolution and diversity of populations and species result from the combined influence of biotic and abiotic components of the region they occupy. Climatic and geological changes interact over broad spatial and temporal scales to influence the genetic signature and structure of populations. Over time geographic regions can experience intermittent periods of isolation countered by regional amalgamation. In turn these events can have a profound impact on evolutionary processes such as gene flow, genetic drift, and selection thereby influencing mechanisms of speciation, extinction, and distribution of biota. During the last glacial maxima mammalian populations persisted in forested refugia that existed in ice-free regions. Following glacial recession populations emanated out of refugia tracking the expanding habitat. I examine the historical genetic signature of populations for three independent systems, Dromiciops gliroides, Sorex palustres, and Zapus trinotatus and Z. princeps that occupy temperate forest systems in either North or South America. Each species exhibits a high affinity for the temperate forest and specific elements within this habitat. In general I examine the influence of habitat specificity, dispersal barriers, and geoclimatic events on the structure and evolutionary history of populations. For all taxa examined, population structure was heavily influenced by the historic geoclimatic events more so than the contemporary distribution of associated habitat. For Sorex palustris the generation of distinct lineages seems to be associated with the recent events of the Pleistocene, while for Dromiciops gliroides and the species within the genus Zapus the major lineages identified are likely to predate the Pleistocene and only owe their contemporary distribution to these geoclimatic cycles. Overall my research demonstrates the strong influence of historic climatic events on the distribution of populations and as a generator of variation among populations.