Australian researchers have found that bird species with multiple plumage color forms within in the same population evolve into new species faster than those with only one color form.
The new study, published in the journal Nature, uses information from birdwatchers and geneticists accumulated over decades. The link between having more than one color variation (color polymorphism) like the iconic red, black or yellow headed Gouldian finches, and the faster evolution of new species was predicted in the 1950s by famous scientists such as Julian Huxley, but this is the first research to confirm the theory.
“By confirming a major theory in evolutionary biology, we are able to understand a lot more about the processes that create biodiversity,” said study co-author Dr. Devi Stuart-Fox of the University of 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,” Dr. Stuart-Fox added. “Well known examples of color polymorphic species in these families include the Australian gray goshawk which has a gray and pure white form, the North American eastern screech owl and the Antillean nighthawk, each with gray and red forms.”
The researchers 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.
“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,“ Dr. Stuart-Fox explained.
By modeling evolutionary rates using publicly available genetic information accumulated over a quarter of a century, the researchers 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 shows 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,” said Dr. Andrew Hugall of the University of Melbourne, a lead author of the study.
“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,” the scientist concluded. “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.”