Many models of evolution by sexual selection predict a coevolution of sensory systems and mate preferences, but the genomic architecture (number and arrangement of contributing loci) underlying these characters could constrain this coevolution. Here, we examine how the genomic organization and evolution of the opsin genes (responsible for tuning color vision) can influence the evolutionary trajectory of sexually selected traits across 15 species in the family Poeciliidae, which includes classic systems for studies of color-mediated sexual selection such as guppies, swordtails, and mollies. Although male coloration patterns and the importance of this coloration in female mate choice vary widely within and among genera, sequencing revealed low variability at amino acid sites that tune Long Wavelength-Sensitive (LWS) opsins in this speciose family. Although most opsin genes in these species appear to have evolved along traditional mutation-selection dynamics, we identified high rates of gene conversion between two of the LWS loci (LWS-1 and LWS-3), likely due to the inverted tandem repeat nature of these genes. Yet members of the subgenus Lebistes appear to resist LWS gene conversion. The LWS opsins are responsible for detecting and discriminating red and orange coloration-a key sexually selected trait in members of the subgenus Lebistes. Taken together these results suggest selection is acting against the homogenizing effects of gene conversion to maintain LWS-1/LWS-3 differences within this subgenus.
