Convergent evolution of large functional traits is not uncommon in nature; consider that wings have evolved in several lineages of animals to broaden niches that animals can fill. But more specific convergence, especially in sexual and territorial signals, is rare at best and stirs controversy in the scientific world.
On the surface, it would seem that if two species converge in their signals, it would lead to crossbreeding and antagonistic interactions. But in a paper online today in Evolution, Joseph Tobias and Nathalie Seddon of the University of Oxford show that for two species of antbirds in South America, convergence has nevertheless occurred. Said Tobias in a press release:
In effect, the territorial songs of these birds are more or less interchangeable in design and function. Given that they last shared a common ancestor more than 3 million years ago, it is almost equivalent to humans and chimpanzees – which diverged around 5 million years ago – using the same language to settle disputes over resources.
Tobias and Seddon used playback experiments to test the reactions of the warbling antbird and the yellow-breasted warbling antbird to songs of the other species. The birds reacted to both songs similarly, treating the songs of each species as equally threatening.
The most interesting piece, however, was that Tobias and Seddon also found that other non-territorial signals, such as plumage coloration and mating calls, were highly divergent. The fact that these traits are so different between the species could help prevent crossbreeding or unnecessary confrontation.
Read the paper at Evolution (subscription required).
Tobias, J., & Seddon, N. (2009). SIGNAL DESIGN AND PERCEPTION IN ANTBIRDS: EVIDENCE FOR CONVERGENT EVOLUTION VIA SOCIAL SELECTION Evolution DOI: 10.1111/j.1558-5646.2009.00795.x