hearing gene Prestin reunites echolocating bats

The remarkable high-frequency sensitivity and selectivity of the mammalian auditory system has been attributed to the evolution of mechanical amplification, in which sound waves are amplified by outer hair cells in the cochlea. This process is driven by the recently discovered protein prestin, encoded by the gene PRESTIN: Echolocating bats use ultrasound for orientation and hunting and possess the highest frequency hearing of all mammals. To test for the involvement of Prestin in the evolution of bat echolocation, we sequenced the coding region in echolocating and nonecholocating species. The resulting putative gene tree showed strong support for a monophyletic assemblage of echolocating species, conflicting with the species phylogeny in which echolocators are paraphyletic. We reject the possibilities that this conflict arises from either gene duplication and loss or relaxed selection in nonecholocating fruit bats. Instead, we hypothesize that the putative gene tree reflects convergence at stretches of functional importance. Convergence is supported by the recovery of the species tree from alignments of hydrophobic transmembrane domains, and the putative gene tree from the intra- and extracellular domains. We also found evidence that Prestin has undergone Darwinian selection associated with the evolution of specialized constant-frequency echolocation, which is characterized by sharp auditory tuning. Our study of a hearing gene in bats strongly implicates Prestin in the evolution of echolocation, and suggests independent evolution of high-frequency hearing in bats. These results highlight the potential problems of extracting phylogenetic signals from functional genes that may be prone to convergence.