Above: red-headed Gouldian finch: more dominant and preferred by females
RESEARCHERS HAVE DISCOVERED how the plumage of a wild Australian songbird has maintained distinct colours for generations and actually breaks the rules of evolution.
Gouldian finches have three distinct colour types – red-, black- and yellow-headed – which have existed in the species for thousands of generations: a rare example of such “balance”.
Scientists at the University of Sheffield and Cornell Lab of Ornithology isolated what was happening at the genome level to understand what caused the different head colours. They discovered that a gene called follistatin, which regulates melanin to produce either red- or black-headed finches, is the underlying mechanism that allows this to happen.
But the findings, published in Nature Communications, were unable to categorise the yellow-headed type, which makes up less than 1 per cent of the Gouldian finch population and is produced by a completely different mechanism that is not yet understood.
Lead author of the paper Kang-Wook Kim, from the University of Sheffield’s department of animal and plant sciences, said: “Most people have heard of natural selection, but survival of the fittest cannot explain the colour diversity we see in the Gouldian finch. We demonstrate that there is another evolutionary process – called balancing selection – that has maintained the black or red head colour over thousands of generations.”
The study also found that the red-headed finches are more dominant and preferred by female finches than black-headed birds, but red-heads have evolutionary disadvantages, such as higher levels of stress hormones and poorer reproductive outcomes.
Co-author of the paper David Toews, a PhD researcher at the Cornell Lab, said: “Having distinct colour types – a polymorphism – maintained within a species for a long time is extremely rare. Natural selection is typically thought of in a linear fashion – a mutation changes a trait which then confers some reproductive or survival advantage and the trait eventually becomes the sole type in the population.
“If advantages are cancelled out by concurrent disadvantages, these two colour types can be maintained, that’s balancing selection. Red forms are not as common in the wild, so the counterbalancing pressure reduces the advantage of being red.”
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