Researchers discover genetic reason for the red, yellow and orange bills of Australian finches

Editors' notes

This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility:

fact-checked

peer-reviewed publication

trusted source

proofread

What gives an Australian finch its brilliantly colored red, yellow or orange bill? A major new study has uncovered the genetic switches controlling these distinctive colors, revealing a key piece in the puzzle of how animals develop their coloration.

The research published in Current Biology, reveals how yellow and red bill colors evolved in the long-tailed finch through changes in just a few key genes that control how birds process yellow pigments from their diet.

The study involved researchers from eight institutions across five countries, with the core research conducted by Dr. Daniel Hooper from the American Museum of Natural History in New York and Professor Simon Griffith at Macquarie University in Australia where the species under investigation is found.

"Modern genomic techniques provide us with incredible insight into how relatively subtle genetic changes can lead to profound changes in things like animal color," says senior author Professor Simon Griffith, 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 across populations over time."

Mixing the colors

The study focused on two subspecies of the long-tailed finch found across northern Australia—one with a yellow bill based in the Kimberley region of Western Australia, and the other with a red bill from the Northern Territory. Where these subspecies meet, they produce hybrid offspring with orange bills.

Most long-tailed finches in Australia today have bright red bills, with the color coming from carotenoid (yellow) pigments in the seeds they eat. The birds produce enzymes that chemically turn the yellow pigments from their diet into red pigments, which are deposited in their growing bills.

By analyzing the DNA of more than 900 finches, the researchers identified the exact genetic changes responsible for the different bill colors. They discovered that yellow-billed finches have genetic variations that prevent them from converting yellow dietary pigments into red ones.

"This discovery helps us understand how animals can evolve different color signals, contributing to the amazing colors of nature," says Professor Griffith.

When red-billed and yellow-billed finches mate, their offspring have orange bills. By studying the exact shade of orange in these hybrid birds, researchers could identify the different genes controlling bill color.

These orange-billed hybrids occur naturally in a narrow region just west of Katherine in the Northern Territory.

Seeing red

There's another fascinating twist to the story. Birds use carotenoid pigments for decorative feather, skin and bill colors—but also for vision. These pigments are used in the retinas of their eyes, where tiny oil droplets containing carotenoids help filter light and enable color vision.

This led to a key discovery. While yellow-billed finches don't produce red carotenoids in their bills, 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," Professor Griffith says.

The research team found evidence buried deep in the genome—the complete DNA code for the different forms—that the yellow bill color, which first appeared about 100,000 years ago, provided some evolutionary advantage, allowing the genes for yellow bills to spread into populations of red-billed finches.

"While red-colored bills were the ancestral state for these finches, we can see natural selection has favored the yellow coloration as these populations have mixed," Professor Griffith says.

"This tells us that having a yellow bill rather than a red one provided some benefit to these birds over many generations."

The study provides new insights into how animal coloration evolves and may help explain similar color variations seen in other bird species around the world.

More information: Daniel M. Hooper et al, Spread of yellow-bill-color alleles favored by selection in the long-tailed finch hybrid system, Current Biology (2024). DOI: 10.1016/j.cub.2024.10.019

Journal information: Current Biology

Provided by Macquarie University

This content was originally published on The Macquarie University Lighthouse.