What does a dolphin have a common with a bat? Quite a bit more than expected, it turns out.
A new paper published in the scientific journal Nature reports that bats and dolphins share genetic signatures that correlate to echolocation – the ability to emit sounds and listen to their echoes to determine the position of distant objects – in 200 regions of the genome. The research offers evidence to support a burgeoning idea in genomics that animals that inhabit similar environments might, independent of each other, evolve to have similar genetic makeups.
The most recent common ancestor of bats and whales lived at least 60 million years ago, says Joe Parker, a biologist at Queen Mary University of London and a coauthor on the paper, in an email interview. It’s improbable that this ancestor could echolocate, but both bats and dolphins have been using some form of echolocation for at least 10 to 20 million years, he said. That means that, in the some 40 million years following the split, two unrelated and otherwise dissimilar animals developed the same innovation.
This process through which unrelated animals evolve the same traits or features is called convergent evolution. Animals living in similar habitats and facing similar environmental pressures develop almost identical adaptive qualities that natural selection fingers for survival.
At first glance, it would seem as though the environments of bats and dolphins’ are radically different, but both animals in fact share a need to find their ways through dim light, be it in the depth of a cave or an ocean.
“Both have to catch prey and avoid obstacles in environments where vision isn't particularly useful,” says Dr. Parker. “Hence there's a common pressure to develop another sense there.”
Convergent evolution is seen all around the planet: the hedgehog and the echidna, a cousin to the platypus, both have spine-covered bodies; the shark and the ichthyosaur, an extinct reptile, both evolved streamlined bodies primed for swimming.
But whether or not those physical similarities are rooted in genetic similarities has not been well understood. Even if dolphins and bats have similar physical capabilities, the genetic infrastructure supporting echolocation could be different in the two animals. In other words, dolphins and bats could have different genes that displayed the same phenotype, an organism’s observable qualities.
“It was previously assumed that since they are unrelated, their genomes and physiologies were different, and so the same problem would be solved by different means in each animals,” says Parker.
Still, some papers had begun to probe at a genetic basis for convergent evolution. One paper, published in Proceedings of the National Academy of Sciences in 2009, had found some evidence for genetic underpinnings to convergent evolution between snakes and lizards.
This new paper, plumbing the entire dolphin and bat genomes, is the largest yet search for genetic evidence of convergent evolution. The researchers used a computer program to sift through and compare the full genomic sequences of 22 mammals, including dolphins and both echolocating and non-echolocating bats. The results show evidence of convergent evolution in almost 200 different genomic regions, most in genes associated with hearing and vision. Those correlations were not found between the non-echolocation-using animals and the echolocating bats and dolphins.
“A few dozen would probably have surprised us,” says Parker, of the 200 genomic regions. “These results give us an idea that in some circumstances, the solutions natural selection happens upon can be similar in unrelated animals right down to the molecular level.”
Still, it is not yet clear exactly what all the implicated genes do, says Parker. More work is still needed to pinpoint the roles that each of the genes play in echolocation, as well on better understanding how natural selection targeted those genes for evolutionary success, he said.