December 7, 2010
TORONTO, ON – While the tropics are home to the vast majority of plant and animal species on Earth, new research on songbirds suggests evolution actually happens faster in places that are located far away from the equator.
Jason Weir, assistant professor of evolutionary biology at the University of Toronto Scarborough (UTSC), measured the differences in length and complexity of song in more than 100 closely related pairs of songbird species, in order to estimate how fast evolution might be occurring between each pair.
Conventional wisdom has held that speciation—the process by which new species are created—occurs in tropical regions at higher rates than anywhere else, explaining why the tropics are such a hotbed of biological diversity.
But when Weir and his colleague, David Wheatcroft at the University of Chicago, plotted their results against the locations where the birds are found, they discovered the farther away a species was from the equator, the faster the evolutionary change.
“Our results show the fastest rates of song evolution in places where diversity is relatively low,” says Weir. “This is surprising, because it suggests that a fast evolutionary pace does not drive high biodiversity. We are going to have to rethink why places like the Amazon have so many species.”
One explanation may lie with the sexual behaviour of female birds. In higher latitudes, breeding seasons become shorter, and females must select their mates much faster than they do at the equator. This means there is a great deal of pressure on the males to evolve highly distinct and complex songs in order to attract these highly motivated females.
“Females are always looking for the sexiest singers,” says Weir. “But at higher latitudes, with shorter breeding seasons, females may not have time to evaluate the males’ other qualifications as they do in the tropics. This pressure would likely drive the rapid evolution of complexity in birdsong. The higher the latitude, the sexier the singers have to be.”
The study is currently published online in the Proceedings of the Royal Society B.
For more information, please contact:
Jason Weir, lead author
Media and communications assistant
University of Toronto Scarborough