Adaptive Evolution Of Mammalian Functional Genes-Evolutionary Studies On Cldn14in Echolocating Whales And RNASE1Gene Duplication In Insect-eating Bats

We discussed the adaptive evolution of mammals based on two aspects. One is about the mechanisms of echolocation in whales and bats, the other is on the molecular adaptive evolution of bats dietary switch. After the previous investigation on genes including Prestin, Kcnq4, Chrna10, AGT and GLUT4, we add more examples on molecular adaptive evolution in mammals.Toothed whales and bats have independently evolved specialized ultrasonic hearing for echolocation. Recent findings have suggested that several genes including Prestin, Tmcl, Pjvk and Kcnq4appear to have undergone molecular adaptations associated with the evolution of this ultrasonic hearing in mammals. Here we studied the hearing gene Cldn14, which encodes the claudin-14protein and is a member of tight junction proteins that functions in the organ of Corti in the inner ear to maintain a cationic gradient between endolymph and perilymph. Particular mutations in human claudin-14give rise to non-syndromic deafness, suggesting an essential role in hearing. Our results uncovered two bursts of positive selection, one in the ancestral branch of all toothed whales and a second in the branch leading to the delphinid, phocoenid and ziphiid whales. These two branches are the same as those previously reported to show positive selection in the Prestin gene. Furthermore, as with Prestin, the estimated hearing frequencies of whales significantly correlate with numbers of branch-wise non-synonymous substitutions in Cldn14, but not with synonymous changes. However, in contrast to Prestin, we found no evidence of positive selection in bats. Our findings from Cldn14, and comparisons with Prestin, strongly implicate multiple loci in the acquisition of echolocation in cetaceans, but also highlight possible differences in the evolutionary route to echolocation taken by whales and bats. Pancreatic ribonuclease gene (RNASE1) was previously shown to have undergone duplication and adaptive evolution related to digestive efficiency in several mammalian groups that have evolved foregut fermentation, including ruminants and some primates. RNASE1gene duplications thought to be linked to diet have also been recorded in some carnivores. Of all mammals, bats have evolved the most diverse dietary specializations, mainly including frugivory and insectivory. Here we cloned, sequenced and analysed KNASE1gene sequences from a range of bat species to determine whether their dietary adaptation is mirrored by molecular adaptation. We found that seven insect-eating members of the families Vespertilionidae and Molossidae possessed two or more duplicates, and we also detected three pseudogenes. Reconstructed RNASE1gene trees based on both Bayesian and maximum likelihood methods supported independent duplication events in these two families. Selection tests revealed that RNASE1gene duplicates have undergone episodes of positive selection indicative of functional modification, and lineage-specific tests revealed strong adaptive evolution in the Tadarida β clade. However, unlike the RNASE1duplicates that function in digestion in some mammals, the bat RNASE1sequences were found to be characterised by relatively high isoelectric points, a feature previously suggested to promote defense against viruses via the breakdown of double-stranded RNA. Taken together, our findings point to an adaptive diversification of RNASE1in these two bat families, although we find no clear evidence that this was driven by diet. Future experimental assays are needed to resolve the functions of these enzymes in bats.