Colour variation speeds up evolution

By confirming a major theory in evolutionary biology, scientists will be able to understand the processes that generate biodiversity. Image: Shutterstock.

Decades of data gathered by bird watchers and geneticists have helped confirm a 60-year-old theory of evolution.

Australian researchers have found that bird species with multiple plumage colour forms (polymorphism) within the same population evolve into new species faster than those with only one colour form (monomorphism). The link between having more than one colour variation — such as the iconic red, black and yellow headed Gouldian finches — and the faster evolution of new species was predicted in the 1950s by scientist Julian Huxley, but this is the first research to confirm the theory.

Researchers Dr Devi Stuart-Fox and Andrew Hugall of the University of Melbourne believe that by confirming a major theory in evolutionary biology we will be able to understand a lot more about the processes that create biodiversity.

“We’re trying to find out why there are certain factors, or catalysts, that make some groups speciate rapidly, so they diversify, while others are evolutionary dead-ends,” says Stuart-Fox. “If we want to know what generates all the biodiversity we see on the earth, then identifying these general patterns is important.”

Polymorphism occurs in many animals, including fish, lizards, butterflies and snails. Stuart-Fox and Hugall usually work with lizards in their research, however they needed big genetic data sets and biological information on the animals for their research — data which isn’t available for lizards. Thanks partly to birdwatchers, there is copious amounts of information on colour variation in birds.

“Classic examples of colour polymorphism include snails with different shell banding patterns and birds with different head or wing colours. Different colour forms often differ in other ways, like in behaviour or physiology, so they should be able to persist in a greater range of environments. This might make them more prone to ultimately evolving into new species,” says Stuart-Fox.

Polymorphism is quite rare, so researchers needed to look at a lot of species to identify a general evolutionary pattern. The Melbourne researchers collected data on five families, ranging from about 70 to 250 species in each family, including four families of birds of prey: hawks and eagles, owls, falcons and nightjars. They also did an analysis of songbirds, which included more than 4100 species.

Researchers used genetic data from Genbank — a large DNA sequence database — as well as world bird databases like the International Ornithological Congress and Avibase, which has 5 million records on 10,000 species. Stuart-Fox and Hugall generated big family trees to show the evolutionary relationships among living species. This allowed them to model rates of evolution and rates of transition between having multiple colour forms and only having a single colour form.

“We found that when you have multiple colour forms, you evolve into new species at a faster rate, but they are new species with only one colour form, generally, so in the process, the polymorphism is lost,” explains the researcher.

The next step in the scientist’s research is to understand why this evolutionary process is sped up by colour polymorphism. Stuart-Fox says: “We’re getting some hints in our work and the work of others at some explanations, but the next step is to look for general patterns among polymorphic species or at specific processes in individual species.”


Source: The Melbourne Newsroom


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