Abstracts (first author)
Functional haemoglobin divergence between bank vole populations of different refugial origins
Much has been learned about the post-glacial partitioning of phylogeographic lineages in various species, yet little is known of the extent to which their distributions have been determined by adaptive differences. We have addressed this issue by studying the genetic basis of haemoglobin (Hb) polymorphism in the bank vole (Clethrionomys glareolus). It is evident that at the end of the last glaciation, bank voles colonized Britain from two different source populations that were already isolated and genetically divergent. Regions colonised by the two lineages can be identified from mtDNA phylogeography and are fixed for different electrophoretically detectable Hb variants. Since modifications of Hb structure and function often play a key role in adaptation to climate and altitude, it has been suggested that the geographical pattern of bank vole Hb variation in Britain may reflect some type of environmental selection favouring the HbS type in the north and the HbF type in the south. We have cloned the genes coding for bank vole Hb by RACE-PCR and assessed their relative expression by RNA-Seq, in order to determine whether the alpha or beta chain polymorphism, and how many loci, underlie the two Hb variants. The results demonstrate that a single amino acid replacement mutation, 52(D3)Ser/Cys, in the major expressed beta globin gene underlies the difference between HbS and HbF. The same polymorphism segregates also at the second, minor expressed beta globin gene, suggesting a possible functional interplay between the two paralogs. The exposed location of the thiol group of 52(D3)Cys on the surface of HbF molecule and the ability to form intermolecular disulphide bonds are indicative of its reactivity and therefore potential involvement in physiologically relevant redox reactions. We suggest that antioxidant potential of the reactive Cys in HbF may convey selective advantage over HbS and contribute to the geographical partitioning of the two bank vole lineages in Britain.