The findings add to a body of research suggesting that climate change is forcing evolution in some animals at a rapid pace. Scientists say this work — accelerated by advances in genomic sequencing technology — helps understand how wildlife can cope and respond to the pressures of rising global temperatures.
In the case of the southwestern willow flycatcher, the researchers found that the birds today are more likely to possess beneficial genes associated with handling heat stress than a century ago.
“When people hear ‘evolution,’ they think it will take thousands or millions of years, but this study shows that it can happen incredibly quickly with climate change,” said Allison Shultz, an ornithologist at the Natural History Museum of Los Angeles County who helped provide historic samples for the study, which was published in Nature Climate Change in June.
Many studies of organisms have documented changes that can be traced to a warming planet — such as certain plants growing smaller leaves during particularly hot summers. But these organisms don’t necessarily pass along these changes to their offspring, as the researchers documented with the flycatcher, explained Sheela Turbek, a postdoctoral fellow at Colorado State University who led the study.
The southwestern bird, which the National Park Service says makes a “distinctive sneezy ‘fitz-bew’ song,” was listed as a federally endangered species in 1995. It is threatened by not only climate change, but also the loss of habitat along riverbanks and other areas where it breeds. The songbirds, which can’t sweat, pant to get relief from heat.
The researchers sequenced the DNA of over 200 contemporary willow flycatchers from across the bird’s breeding range. They then compared the sequences to those of museum specimens collected in the late 1800s and early 1900s near San Diego.
This required taking small clippings from the birds’ toe pads. “That’s not a ton of genetic material to work with,” Turbek said.
The results came as a surprise: The willow flycatchers near San Diego today were more likely to have beneficial genes that help them handle wet and humid days than those in the past, suggesting the birds evolved in response to the changing climate.
The researchers determined that these genes may have been introduced into the birds as they intermixed and bred with willow flycatchers from the Pacific Northwest and Desert Southwest. The new genetic material that proved helpful for survival would then have been passed on.
Turbek said this finding could inform future conservation efforts. For example, scientists could mix animals from different regions, potentially introducing helpful genes from the animals better adapted to the new climate conditions and giving the vulnerable populations a leg up.
How animals adapt to climate change
Animals confronted by climate shifts have three options, said Sally Aitken, a forestry professor at the University of British Columbia who co-wrote a textbook on conservation and population genomics.
They can move geographically, she said, or, in some cases, express traits better suited to the environment within their existing genome — no evolution required.
They can also genetically adapt, a process by which an organism’s genome changes over generations in response to pressures from its environment.
Turbek and her team are not the only ones who have documented such changes in animals. Earlier research on genetic adaptation focused on animals like fruit flies with smaller, well-studied genomes. And in recent years, technological advances have allowed researchers to take on a menagerie of animals with more complicated genomes, such as chipmunks and lizards.
Animals with the largest genomes, such as salamanders and grasshoppers, are still out of reach, said Renee Catullo, a biology lecturer at the University of Western Australia who wrote a literature review on the subject. “But we’re getting some unbelievable information from old specimens that 10 years ago we thought would have been impossible,” she added. “It’s a huge acceleration.”
However, Ary Hoffmann, the chair of ecological genetics at the University of Melbourne, cautioned that there are challenges in attributing changes in genomes to climate change adaptation. A 2005 paper on fruit flies he published in Science was one of the first to find genetic adaptation attributable to climate change. But it focused on a single gene and a flipped piece of chromosome that were well studied, not on entire genetic regions like the songbird study.
He said the songbird study is a starting point, but drawing connections between genetic changes and climate change is more difficult when there are multiple genes involved or when the genes in question are not as well-studied.
“You often get situations like this where a technology takes off, and people get excited about it,” he said. “But they don’t realize they need to be much more cautious about how they interpret what they find.”
But Shultz, the ornithologist, said the study results provide some hope that the songbird can adapt to climate change.
“I absolutely think this is good news,” Shultz said.
