Colonization history in Fennoscandian rodents

Fennoscandia probably constitutes one of the best places on earth to study faunal history. During the height of the most recent glacial period Fennosc andia was completely, covered with ice. Thus, the majority of extant specie s must originate from ancestors who survived thtr latest glaciation in non- glaciated areas outside Fennoscandia. Moreover, the geography and geologica l history of Fennoscandia suggests that post-glacial recolonization by land mammals must have been restricted to specific routes in time and space Phy logeographic surveys of mitochondrial DNA (mtDNA) variation in Fennoscandia n rodents have demonstrated thai glacial history and patterns of post-glaci al colonization have played a major role in shaping present day patterns of genetic differentiation within species. Thus, the generic imprints of hist orical demographic conditions and vicariant geographic events have been ret ained within species and can be used to infer the history of populations. T he field vole (Microtus agrestis) is used to illustrate these data and proc esses. Comparisons are made with phylogeographic surveys of the bank vole ( Clethrionomys glareolus), the eastern louse mouse (Mus musculus) and the wo od lemming (Myopus schisticolor) as well as a few other species foe which l ess extensive studies have been performed. The main patterns of post-glacia l colonization of Fennoscandia by rodents are described. The effects of tim ing and patterns of colonization on contemporary population genetic structu re and levels of genetic variation are discussed. Specifically, the effects of hybridization and introgression as well as founder events and bottlenec ks are explored. (C) 1999 The Linnean Society or London.