Over the years, researchers have used presumptively neutral molecular variation to infer the origins of current species' distributions in northern latitudes (especially Europe). However, several reported examples of genic and chromosomal replacements suggest that end-glacial colonizations of particular northern areas may have involved genetic input from different source populations at different times, coupled with competition and selection. We investigate the functional consequences of differences between two bank vole (Clethrionomys glareolus) haemoglobins deriving from different glacial refugia, one of which partially replaced the other in Britain during end-glacial climate warming. This allows us to examine their adaptive divergence and hence a possible role of selection in the replacement. We determine the amino acid substitution Ser52Cys in the major expressed β-globin gene as the allelic difference. We use structural modelling to reveal that the protein environment renders the 52Cys thiol a highly reactive functional group and we show its reactivity in vitro. We demonstrate that possessing the reactive thiol in haemoglobin increases the resistance of bank vole erythrocytes to oxidative stress. Our study thus provides striking evidence for physiological differences between products of genic variants that spread at the expense of one another during colonization of an area from different glacial refugia.

Department of Animal Physiology and Immunology Institute of Experimental Biology Faculty of Science Masaryk University Brno 61137 Czech Republic

Department of Ecology and Evolutionary Biology Cornell University Ithaca NY 14853 USA

Laboratory of Fish Genetics Institute of Animal Physiology and Genetics Academy of Sciences of the Czech Republic Liběchov 27721 Czech Republic

Laboratory of Molecular Ecology Institute of Animal Physiology and Genetics Academy of Sciences of the Czech Republic Liběchov 27721 Czech Republic

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