2008 Alaska Park Science Symposium
October 14, 2008
Analyses of mtDNA, Y and X Chromosome Sequences Reveal Congruent Phylogeographic Structure and Cryptic Speciation in Arctic Lemmings (Lemmus)
Vadim B. Fedorov1, Anna V. Goropashnaya2
1Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK, 99775, USA, fnvf@uaf.edu
2Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK, 99775, USA
Arctic lemmings demonstrated strong mtDNA phylogeographic structure across the Holarctic with three significant longitudinal divisions. The depth of phylogeographic splits (mtDNA cytochrome b net divergence 8.7%; 6.2% and 4.5%) suggests continuous vicariant separation over several glacial-interglacial periods. In order to confirm independent evolutionary history of the phylogeographic groups detected by mtDNA variation, we studied sequence variation in introns of Y and X chromosomes. Reciprocal monophyly of all groups revealed by variation in maternal mtDNA marker was supported by genealogy based on variation in paternal Y chromosome. Genealogy based on variation in biparental X chromosome was congruent to the mtDNA and Y chromosome phylogenies, with exception for non reciprocal monophyly of the two Eurasian phylogeographic groups. This probably indicates incomplete lineage sorting due to three times lager effective size for X chromosome. Similar to other mammalian species, nucleotide diversity estimates were highest for mtDNA (7.3%), X chromosome (1.1%) and lowest for Y chromosome (0.7%). To investigate extent of introgression, we screened variation in all three markers across an area of secondary contact between the Beringian and Eastern phylogroups in east Alaska – Yukon. Analysis of 65 lemmings, including 44 males, detected 11 hybrids (17%). This finding possibly indicates existence of some reproductive isolation and suggests cryptic speciation in the Beringian lemmings due to recurrent isolation by the continental ice sheet during the Pleistocene. The analysis with the three different types of genetic markers facilitates inference on evolutionary history.
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