Levsen, Nicholas , Tiffin, Peter , Olson, Matthew S. .
Tree species evolution in the Ice Age: understanding the divergence of Populus balsamifera and Populus trichocarpa (Salicaceae).
The Quaternary Ice Age was geologically and climatically dynamic and the environmental processes concomitant with this period had significant consequences for patterns of biodiversity. Though it has been well demonstrated that rapid Quaternary climate change and relatively short-lived glacial cycles greatly influenced levels of intra-specific genetic diversity in many lineages, their role in promoting macro-evolutionary change remains controversial. This is particularly true of typically slow-maturing lineages (e.g., trees, corals), in which modern species are often morphologically indistinguishable from putative Tertiary ancestors. To determine whether the divergence of some tree species may be associated with Pleistocene-age physiographic events, we analyzed genetic and ecogeographic data from the temperate tree species Populus balsamifera and P. trichocarpa. Thirty-four loci (32 nDNA and 2 cpDNA) were used to estimate speciation parameters (e.g., divergence time, effective population size) under an IM (Isolation-Migration) model. In addition, species distribution models (SDMs) were constructed for the last glacial maximum (LGM) and the last inter-glacial (LIG) to identify glacially-mediated range shifts that could have promoted allopatric speciation. The divergence time for P. balsamifera and P. trichocarpa was estimated at approximately 800 Ka, a period roughly coincident with the mid-Pleistocene transition and the beginning of much more extensive continental glaciation, while analyses of SDMs demonstrated increased separation of the respective species ranges during the glacial and inter-glacial periods of the Pleistocene. These results suggest that, in specific cases, the physiographic processes of the Quaternary Ice Age were sufficient to promote speciation in temperate tree lineages.
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1 - University of Alaska Fairbanks, Institute of Arctic Biology, 902 Koyukuk Drive, Fairbanks, AK, 99775, USA
2 - University of Minnesota, Plant BIology, 1445 Gortner Avenue, Saint Paul, MN, 55108
Quaternary Ice Age
species distribution models
Presentation Type: Oral Paper:Papers for Sections
Location: 555A/Convention Center
Date: Monday, August 2nd, 2010
Time: 1:45 PM