Olfactory receptors and behavioural isolation: a study on Microtus voles

Genetic variation in olfactory receptors may trigger mate choice, suggesting that olfaction has undergone diversifying selection in diverging populations and may contribute to premating reproductive isolation. In the present study, we analysed two olfactory receptor genes as candidate barriers of reproductive isolation between two recently divergent voles: Microtus lusitanicus and Microtus duodecimcostatus. In addition, evolutionary relationships and signs of positive selection were inferred in a European subgenera context, based on 76 samples from 14 species. DNA sequence analysis revealed the presence of shared haplotypes among various Microtus species. Tests of selection detected negatively selected amino acids in the extracellular loops of both olfactory receptors and a majority of negatively selected residues in the transmembrane helices, the most variable regions responsible for the reception of odorants. Our findings suggest that, for several Microtus species, including M. lusitanicus and M. duodecimcostatus, these proteins probably recognise conserved odour cues not related to behavioural isolation