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The link between having more than one color variation (color polymorphism) like the red, black, or yellow headed Gouldian finches, and the faster evolution of new species was predicted in the 1950s by scientists such as Julian Huxley, but the new study, published in the journal Nature, is the first to confirm the theory.

The global study that uses information from birdwatchers and geneticists accumulated over decades clarifies the processes that create biodiversity, says Devi Stuart-Fox, from the University of Melbourne’s zoology department.

The Australian grey goshawk has a grey and pure white form, an example of color polymorphism. (Credit: U. Melbourne)

“We found that in three families of birds of prey, the hawks and eagles, the owls, and the nightjars, the presence of multiple color forms leads to rapid generation of new species.

“Well known examples of color polymorphic species in these families include the Australian grey goshawk which has a grey and pure white form, the North American eastern screech owl and the Antillean nighthawk, each with grey and red forms.”

Stuart-Fox and study co-author Andrew Hugall, now based at the Melbourne Museum, focused on birds because although color polymorphism occurs in many animals (such as fish, lizards, butterflies, and snails), there is a wealth of information on color variation in birds, as well as on species classification (taxonomy), partly thanks to birdwatchers or “‘twitchers.”

“We looked at five bird families with a high proportion of color polymorphism and compared their rates of evolution with those with only one color form,” Stuart-Fox says.

By modeling evolutionary rates using publicly available genetic information accumulated over a quarter of a century, the study found that color polymorphism speeds up the generation of new species.

Color polymorphic species tend to evolve into species with only one color form (monomorphic), explaining why existing species with different color forms are relatively young and also rare.

The study found that color polymorphic species were younger not only in the birds of prey but in the songbirds, which account for more than half of the world’s bird species.

When scientists like Julian Huxley proposed that color polymorphism speeds up the generation of new species over half a century ago, they did not have the huge amounts of data needed to support it, Hugall says.

“Using many decades of natural history information and 25 years of genetic sequence information we were able to generate the massive family trees, such as a tree of more than four thousand songbirds, needed to model rates of bird evolution in this study.

“Now that we’ve identified this pattern for the first time, our next step is to test some of the explanations proposed for why color polymorphism leads to accelerated evolution.”

More news from the University of Melbourne: http://newsroom.melbourne.edu/