They are known as some of the brightest, loudest, most unusual looking, and least understood birds that glide across our skies. Some have bulbous crests, long fleshy wattles, or Elvis-worthy pompadours, along with electric blue, deep purple, or screaming orange feathers. Thanks to a comprehensive new evolutionary ‘tree of life’ created for the tropical cotinga family of South America, the door is now open to new discoveries about the 60 plus species in this incredibly varied group of birds.
“Our study provides comprehensive insight into how nearly all the cotinga species are related to each other going all the way back to the common ancestor,” says lead author Jake Berv, a Ph.D in the Fuller Evolutionary Biology Lab at the Cornell Lab of Ornithology. “No previous attempts to understand the evolutionary history of this group have included genetic samples from nearly all the existing species.”
Berv began sequencing DNA samples and collecting data back in late 2010 whilst working as a lab technician at Yale University with co-author Prof. Rick Prum, a leading expert on cotingas. The understanding of how one species is related to another within this group enables scientists to trace the evolution of certain traits and behaviours.
Berv and Prum have already begun this process. They wanted to learn if the evolution of differently coloured males and females in this group of birds (sexual dimorphism) is directly linked the to the breeding system in which males have multiple mates (polygyny). Darwin first proposed the theory that the increased pressure of sexual selection in polygynous birds encouraged the development of colour differences between the sexes. This seems to be correct for many species- but not the cotingas. When Berv and Prum examined the patterns of evolution for these two traits across their new tree of life, it turned out that they didn’t quite match up perfectly. The statistics they calculated also supported the conclusion that these traits might be evolutionary “de-coupled” in the cotingas.
Sexual selections seems to have played a crucial role in the evolution on non-plumage gender differences in some cotinga species.
“In one case, the Screaming Piha, the males and females look alike but the male sings one of the loudest songs on the planet,” says Yale’s Rick Prum. “That means male-female plumage difference alone is not evidence for sexual selection because sexual selection is also driving other traits such as voice and behaviour.”
“One of the biggest analytical differences between what we’ve done and past work is that we used a ‘species tree’ approach, which is potentially more accurate than what is typically applied to genetic data,” says Berv. “We ran our data through more traditional types of analyses as well, and all of them strongly supported a consistent evolutionary ‘tree of life’. We hope other scientists who are interested in these birds take our phylogeny and do all sorts of great things with it.”
Contributing Source: Cornell University
Header Image Source: Wikimedia
