Bats and dolphins are two of the most celebrated users of echolocation, employing high-frequency sounds to locate prey, find their way, or to communicate. Now a new set of findings in Current Biology show that not only do the two different kinds of mammals use the same method, they also evolved nearly the exact same molecular means for hearing at high frequencies. That second part was a surprise, study author Stephen Rossiter says:
"It's common on a morphological scale but it's assumed not to occur at a DNA level because there are so many different ways to arrive at the same solution" [BBC News]
. That is, while it's quite common for different species to separately evolve similar features—like the tusks of elephants and walruses—it's quite unlikely that natural selection working in separate species would settle an essentially identical gene and protein for growing tusks, hearing high-frequency sounds, or anything else. Or so the thinking went. The gene in question, and the protein it encodes, are both called prestin. It's present in the short hairs of the inner ear, the researchers say.
Prestin changes shape when exposed to high-frequency sound, and this in turn deforms the fine hair cells, setting off an electrical impulse to the brain. So the protein has the important jobs of detecting and selecting high-frequency sounds for amplification [New Scientist]
. Prestin is common across mammals, although many different variants exist; mutations of the human version cause people to lose high-frequency hearing. But the prestin proteins that echolocating dolphins and bats evolved are almost identical, the study says. By contrast, bats that don't use sonar don't have that version of the protein, despite the fact that they're much more closely related to their fellow bats than dolphins are. For biologist David Pollock, who wasn't involved in the study, this new could open a new window to understanding protein evolution.
These findings, combined with a previously identified example of molecular convergence in snake and lizard mitochondrial genomes, suggest that molecular convergence may be more common than scientists realize -- "it's [just] not always easy to detect," Pollock said [The Scientist]
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Image: flickr / Ken Lund