Convergent evolution describes the acquisition of the same biological trait in unrelated lineages, whereas, parallel evolution is the development of a similar trait in related, but distinct, species descending from the same ancestor, but different clades. An iconic example of either of them via natural selection is echolocation by bats, toothed whales and dolphins. Echolocation, also called biosonar, is being used to realize navigation and hunting.
Although, the previous research about echolocation was mainly focusing on the high frequency sound signals processing by animals’ cochleae. Echolocation is much more complicated than that and the most important factors of it include cochlear amplification, nerve transmission, and signal re-coding. Herein, to reveal the underneath molecular mechanisms, in his newly updated results, Dr.SHEN Yongyi (Kunming Institute of Zoology, the CAS) and his colleagues screened three genes that play different roles in this auditory system. Cadherin 23 (Cdh23) and its ligand, protocadherin 15 (Pcdh15), are essential for bundling motility in the sensory hair. Otoferlin (Otof) responds to nerve signal transmission in the auditory inner hair cell.
According to Dr. SHEN, signals of parallel evolution occur in all three genes in the three groups of echolocators—two groups of bats (Yangochiroptera and Rhinolophoidea) plus the dolphin. Cdh23 and Pcdh15 constitute part of the mechanical link within the hair bundle of the ear. Both genes showed signals of both convergent evolution and positive selection, which implied they may have co-evolved to optimize cochlear amplification. Moreover, the expression level of Otof in different cerebral cortexes, bat species and developmental stages also imply that Otof plays an important role in the transmission of signals in the brain during echolocation.
These results indicated that positive selection, parallel evolution, and perhaps co-evolution and gene expression affect multiple hearing genes that play different roles in audition, including voltage and bundle motility in cochlear amplification, nerve transmission, and brain function.
In summary, this study has synthesized gene sequence, gene expression and gene evolution of echolocation. More importance, this is the first time revealed that the molecular mechanisms of brain and its relative genes expression are the pivotal players of echolocation evolution.
The main findings of this study have been published on Plos Genetics (http://www.plosgenetics.org/article/info%3Adoi%2F10.1371%2Fjournal.pgen.1002788).
