Australian Finches Have Different Colored Bills Due To A Few Genes That Dictate How They Process Yellow Pigments From Their Diet
If you’ve ever seen an Australian finch, you know that it has a brightly colored red, orange, or yellow bill. But how and why do these birds develop one color over another?
A new study has revealed how red and yellow bill colors evolved in the long-tailed finch. It turns out that changes in just a few key genes dictate how the birds process yellow pigments from their diet.
Researchers from eight institutions across five different countries focused their studies on two subspecies of the long-tailed finch in Australia.
One had a yellow bill and was from the Kimberley region of Western Australia, while the other had a red bill and was based in the Northern Territory.
In the areas where these two subspecies meet, they produce hybrid offspring with orange bills. The orange-billed hybrids occur in a small region to the west of Katherine in the Northern Territory.
Today, most long-tailed finches in Australia have bright red bills. The red hue comes from carotenoid (yellow) pigments in the seeds they consume.
The birds produce enzymes that turn the yellow pigments into red ones, which are then deposited in their growing bills.
“Modern genomic techniques provide us with incredible insight into how relatively subtle genetic changes can lead to profound changes in things like animal color,” said Simon Griffith, the senior author of the study and a professor from Macquarie University’s School of Natural Sciences.
“Now, 165 years after Darwin first published his theory of evolution, we can see exactly how the frequency of these genes changes in populations over time.”
Bob – stock.adobe.com – illustrative purposes only, not the actual finches – pictured above a pair of Australian finches sit on a tree branch
The researchers were able to analyze the DNA of over 900 finches and identified the genetic changes that are responsible for the different bill colors.
They found genetic variations in finches with yellow bills that prevent them from converting carotenoid pigments into red ones.
By examining the exact shade of orange in the hybrid offspring of these birds, the researchers could determine which genes controlled bill color.
Birds use carotenoid pigments for the color of their feathers, bills, and skin, but they’re also used for vision.
These pigments are applied to the retinas of their eyes. Small oil droplets containing carotenoids aid in filtering light and color vision.
Yellow-billed finches don’t produce red carotenoids in their bills; however, they can still make them in their retinas.
“It’s not that yellow-billed birds lack the genes for making red coloring; rather, they control these genes differently in different parts of their bodies,” said Griffith.
Evidence shows that the yellow bill color, which first appeared around 100,000 years ago, gives the birds an advantage in the wild. Since then, the genes for yellow bills have spread into the populations of finches with red bills.
Red was the original color for these finches’ bills, but natural selection has demonstrated that the yellow coloration benefited the birds more than the red over many generations.
The study was published in Current Biology.
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