London, April 26 : Evolutionary biologists have determined that isolation might not be necessary for the formation of new species, taking the example of cave-dwelling salamanders that have evolved into separate species from their surface-dwelling kin despite regularly interbreeding.
According to a report in New Scientist, Matthew Niemiller, an evolutionary biologist at the University of Tennessee in Knoxville, US, and his colleagues carried out the study.
During their research work, the team saw hints of hybridisation between Tennessee cave salamanders and the surface-dwelling spring salamander.
The researchers sequenced DNA samples from 109 cave and spring salamanders from 43 locations throughout Tennessee.
They then plugged the data into a sophisticated computer model that compared possible evolutionary histories for the salamanders and calculated which scenario provided the most likely explanation for the genetic patterns observed.
The results suggested that the cave salamanders could not have evolved in isolation from the surface species. In fact, the most likely history was one in which spring salamanders regularly interbred with cave salamanders even as the two species were diverging about 2 million years ago.
"Natural selection in the cave salamander for traits helpful for life in caves - such as sharper non-visual senses and a permanently aquatic lifestyle - must have been strong enough to override this gene flow between the surface and cave animals," said Niemiller.
Applying the same analysis to other cases where species were thought to have evolved in isolation - both within caves and without - is likely to yield more examples.
"It's very difficult to show that two divergent forms have experienced gene flow," said Niemiller. "It might be more prevalent than we currently recognize," he added.
According to Niemiller, what is interesting is that the migration events cluster fairly early on. This suggests gene flow was initially fairly high, and then as they adapt to the new environment, you get the buildup of barriers due to adaptation, and then gene flow goes down.