Effects of parasite and historic driven selection on the diversity and structure of a MHC-II gene in a small mammal species (Peromyscus leucopus) undergoing range expansion
Genetic diversity may decrease from the centre to the margin of a species distribution range due to neutral stochastic processes. Selection may also alter genetic diversity in non-neutral markers, such as genes associated with the immune system. Both neutral processes and selection on the immune system are thus expected to affect the spatial distribution of such markers, but the relative strength of each has been scarcely studied. Here, we compared the diversity of a neutral marker (mitochondrial cytochrome b) and a selected marker (DRB gene from the MHC-II), in eastern-North American populations of white-footed mice (Peromyscus leucopus), a species known for its role of main reservoir of the Lyme disease. We observed distinct phylogeographic patterns with these two markers, which may be the result of selection pressure acting upon the DRB gene. As predicted by the central marginal hypothesis, we observed a loss of neutral genetic diversity toward the margin of the species distribution. A decrease in diversity was also observed for the DRB gene, likely due to genetic drift and positive selection operated by helminth parasites. Such a loss in genetic diversity at the range margin may slow down the ongoing expansion of P. leucopus, by counterbalancing the effect of global warming on the mouse survival at higher latitude.
KeywordsCytochrome-b gene Major histocompatibility complex diversity Peromyscus leucopus Helminths
We thank the Smithsonian National Museum of Natural History and the Harvard Museum of Natural History for the loan of some tissue samples. We thank S. Leo, S. Turney, field assistants and land owners. Computational resources were provided by the CBGP HPC computational platform, and by the Consortium des Équipements de Calcul Intensif (CÉCI) funded by the Fonds de la Recherche Scientifique de Belgique (F.R.S.-FNRS) under Grant No. 2.5020.11. This work was supported by Belgian FRS-FNRS (Fonds de la Recherche Scientifique) fellowship to AA and to JRM and by financial grants from the Belgian FRS-FNRS (‘‘credits pour brefs séjours à l’étranger’’) to AA and JRM, and from the “Patrimoine de l’université de Liège” to AA. VM is supported by a NSERC DG Grant (RGPIN/341918-2012).
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