Testing the sensory trade-off hypothesis in New World bats.

Detection of evolutionary shifts in sensory systems is challenging. By adopting a molecular approach, our earlier study proposed a sensory trade-off hypothesis between a loss of colour vision and an origin of high-duty-cycle (HDC) echolocation in Old World bats. Here, we test the hypothesis in New World bats, which include HDC echolocators that are distantly related to Old World HDC echolocators, as well as vampire bats, which have an infrared sensory system apparently unique among bats. Through sequencing the short-wavelength opsin gene (SWS1) in 16 species (29 individuals) of New World bats, we identified a novel SWS1 polymorphism in an HDC echolocator: one allele is pseudogenized but the other is intact, while both alleles are either intact or pseudogenized in other individuals. Strikingly, both alleles were found to be pseudogenized in all three vampire bats. Since pseudogenization, transcriptional or translational changes could separately result in functional loss of a gene, a pseudogenized SWS1 indicates a loss of dichromatic colour vision in bats. Thus, the same sensory trade-off appears to have repeatedly occurred in the two divergent lineages of HDC echolocators, and colour vision may have also been traded off against the infrared sense in vampire bats.