Submitted to: Journal of Biogeography
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/18/2006
Publication Date: 1/23/2007
Citation: Waltari,E., Hoberg,E.P., Lessa,E.P., Cook,J.A. 2007. Eastward ho: phylogeographic perspectives on colonization across the beringian nexus. Journal of Biogeography. 34:561-574. Interpretive Summary: The Arctic is among the best examples of a long-term natural experiment related to the effects of global temperature change in structuring biodiversity. Dramatic fluctuations in climate during the Pleistocene led to large ice sheets covering considerable expanses of the Arctic during glacial maxima, affecting large scale movement of terrestrial organisms. Despite massive glacial advances at high latitudes, a large ice-free region extended from Far East Russia to Alaska and northwestern Canada. Called Beringia, this region is notable from a biogeographical perspective for two reasons. First, as an ice-free region, Beringia was one of the largest northern refugia for terrestrial organisms, and has been hypothesized to be critical in the diversification of arctic taxa. Secondly, the Bering Land Bridge of central Beringia served as a filter for terrestrial organisms, allowing selective exchange of Nearctic and Palearctic biotas. We explored the history of Beringia and the northern fauna to develop insights about the past and present distributions of mammals, and an array of associated parasites and pathogens. Studies at the Beringian crossroads provide powerful models for addressing fundamental questions about the evolution of complex host-parasite systems. We reviewed and synthesized phylogeographic studies of Beringian terrestrial and freshwater taxa in order to identify generalized patterns regarding the number, direction, and timing of geographic colonization at the Beringian nexus. We examined 35 studies of trans-Beringian taxa, collating the number, direction, and timing of trans-continental colonizations as reported in the original publications. We found moderate amounts of colonization across Beringia, primarily from Asia to North America, with many events occurring in the Quaternary period. The 35 molecular studies of trans-Beringian organisms we examined continue to research important concepts in arctic biogeography such as cospeciation among arctic taxa and the role of glacial cycles and refugia in promoting diversification, but also indicate new directions and potentially fruitful future prospects. Some of these developing avenues include further insights into the paleoecology of Beringia, the establishment of testable hypotheses, an increase in the use of ancient DNA, and new studies of arctic host-parasite systems highlighting their diversity, biogeography, and response to climate variation and ecological perturbation in evolutionary and ecological time.Inherent in the analysis of high-latitude systems is the assumed role of Pleistocene glaciations in in situ diversification and extinction of many boreal and arctic taxa. Populations located outside the boundaries of Beringia also were important in recolonization of northern deglaciated areas. Other Nearctic refugia have been hypothesized for decades (e.g. Canadian High Arctic), but paleontological and palynological evidence is inconclusive. Several phylogeographic studies of boreal species implicate additional refugia as important in diversification of Arctic taxa and ultimately in structuring communities. These investigations all document a strong signal of historical climate change in the evolution of northern organisms, and corroborate the assertion that fluctuating Pleistocene environments had greater impact on diversification of boreal organisms than on southern biota. Recognition of the critical role of historical climate change on northern biota is relevant to our assessment of the impact of contemporary environments. Current and predicted global climate trends indicate the greatest warming is occurring at high latitudes, and the amount of tundra habitat will be dramatically reduced and replaced by taiga in the near future. Ecological perturbation associated with directional climate warming is further predicted to influence the distribution and dynami
Technical Abstract: Aim To review phylogeographic studies of Beringian terrestrial and freshwater taxa in order to identify generalized patterns regarding the number, direction, and timing of geographic colonization at the Beringian nexus. Location Beringia, the large, historically ice-free region extending from Far East Russia to Alaska and northwestern Canada. Methods We examined 35 studies of trans-Beringian taxa, collating the number, direction, and timing of trans-continental colonizations as reported in the original publications.