Widespread changes scattered across the genomes of distantly related species crafted the trait
Gareth Jones/Univ. of Bristol, England
Despite being separated by millions of years of evolution, dozens of genes in dolphins and bats changed in the same manner to give the species their ability to echolocate. A study, which has received criticism from some scientists, found that similar mutations allowed webs of genes in the animals to contribute to the superpower of being able to “see” with sound.
Biologists have long been interested in convergent evolution, the process by which distantly related species develop similar traits. Echolocation is one of the most famous examples: some species of bats do it, as do bottlenose dolphins and other toothed whales. Researchers have identified a handful of genes for echolocation which are shared across the species. But the extent to which similar mutations radiate throughout the genome to produce a shared trait in distantly related species has been difficult to trace, says evolutionary geneticist Joe Parker from the Queen Mary University of London.
So Parker, fellow Queen Mary scientist Stephen Rossiter and colleagues dug through the genome sequences of nearly two dozen mammalian species to piece together the genes involved in echolocation.
To search for genes that evolved convergently in echolocating animals, the researchers lined up the genomes of 22 mammalian species, only some of which echolocate. The species included the bottlenose dolphin and four bat species whose genomes the researchers sequenced for the study: three bats that echolocate and one that doesn’t. The researchers then used a computer simulation to scroll through the genomes and correlate mutations with ability to echolocate. The researchers report September 4 in Nature that nearly 200 genetic regions stood out as evolving together – far more than the researchers had expected.
“This highly specialized life trait is affecting vast portions of the genetic makeup of the organism, not just one or two genes,” Parker says.
But David Pollock of the University of Colorado School of Medicine warns, “The authors are not really being cognizant of the limitations of their methods.” Pollock, who led a study that traced convergent evolution in lizards and snakes, asserts that the simulations the team used were “fundamentally incapable” of distinguishing between genes that evolved to enable echolocation and those that changed with no noticeable effect on the animals.
Still, Pollock notes the method successfully identified genes already known to play a role in echolocation. It also found many new genes for researchers to explore, he says, including genes involved in hearing, vision, neural processing, and metabolism.
For Ya-Ping Zhang of Yunnan University in Kunming, China, whose team previously discovered convergent evolution between bats and dolphins in some echolocation genes, the genome-wide study took an important step in unraveling the extent of convergent evolution in one trait. “It demonstrated that the analysis at the genome level is necessary and powerful to understand the genetic basis of complex traits,” Zhang says.
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