The survival of vertebrate species is dependent on the ability of individuals to adequately interact with each other, a function often mediated by the olfactory system. Diverse olfactory receptor repertoires are used by this system to recognize chemicals. Among these receptors, the V1rs, encoded by a very large gene family in most mammals, are able to detect pheromones. Teleosts, which also express V1r receptors, possess a very limited V1r repertoire. Here, taking advantage of the possibility to unequivocally identify V1r orthologs in teleosts, we analyzed the olfactory expression and evolutionary constraints of a pair of clustered fish V1r receptor genes, V1r1 and V1r2. Orthologs of the two genes were found in zebrafish, medaka, and threespine stickleback, but a single representative was observed in tetraodontidae species. Analysis of V1r1 and V1r2 sequences from 12 different euteleost species indicate different evolutionary rates between the two paralogous genes, leading to a highly conserved V1r2 gene and a V1r1 gene under more relaxed selective constraint. Moreover, positively-selected sites were detected in specific branches of the V1r1 clade. Our results suggest a conserved agonist specificity of the V1R2 receptor between euteleost species, its loss in the tetraodontidae lineage, and the acquisition of different chemosensory characteristics for the V1R1 receptor.
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