Rhodopsin Molecular Evolution in Mammals Inhabiting Low Light Environments

Zhao, Huabin; Ru, Binghua; Teeling, Emma C.; Faulkes, Christopher G.; Zhang, Shuyi; Rossiter, Stephen J.

In the bats, rhodopsin homologues in species with and without laryngeal echolocation were characterized by similar v ratios, in spite of the fact that the latter (Old World fruit bats) are characterized by larger eyes and are often considered to be more dependent on low light (scotopic) vision. However, evidence of divergent selection was found between these groups. Interestingly, clade models suggested that bats that have evolved high-duty-cycle echolocation had a significantly higher v ratio than other bats (i.e. Old World fruit bats and low-duty-cycle echolocators) (see Supplementary Table S3 , Supplementary Material online). In the absence of positive selection, one possibility is that high-dutycycle echolocators have experienced relaxed selection, perhaps due to a relatively higher dependence on the auditory system. Interestingly these results from bat rhodopsin genes show parallels with the recent results of two other studies of sensory genes in bats. Genetic analyses of medium and shortwave opsins showed that species with high-duty-cycle echolocation have also lost their SWS1 genes via both frame shift and nonsense mutations [22] . Moreover, positive selection on the ancestral branch of this group has also been detected in the Prestin gene, which encodes a motor protein implicated in high frequency hearing that is especially characteristic of this group [49] . Such concordance indicates that multiple genes are impacted by common selection pressures, and raises the possibility that molecular changes at one sensory gene will have direct consequences for genes controlling the same or other sensory modalities, perhaps via trade-offs (see [22] ).