Homoeologous Recombination of the V1r1-V1r2 Gene Cluster of Pheromone Receptors in an Allotetraploid Lineage of Teleosts

In contrast to other olfactory receptor families that exhibit frequent lineage-specific expansions, the vomeronasal type 1 receptor (V1R) family exhibits a canonical six-member repertoire in teleosts. V1r1 and V1r2 are present in no more than one copy in all examined teleosts, including salmons, which are ancient polyploids, implying strict evolutionary constraints. However, recent polyploids have not been examined. Here, we identified a young allotetraploid lineage of weatherfishes and investigated their V1r1-V1r2 cluster. We found a novel pattern that the parental V1r1-V1r2 clusters had recombined in the tetraploid genome and that the recombinant was nearly fixed in the tetraploid population. Subsequent analyses suggested strong selective pressure, for both a new combination of paralogs and homogeneity among gene duplicates, acting on the V1r1-V1r2 pair.