Historical DNA shows how endangered bird evolved to adapt to a changing climate

Contact for reporters:
Allison Sylte
(720)-849-1907
Allison.Sylte@colostate.edu

A new study led by Colorado State University researchers is one of the first to show how wild organisms are evolving in response to climate change. 

The researchers found that a population of the Southwestern Willow Flycatcher – an endangered migratory bird – has shown an increase in genetic variation that allows it to better tolerate the wetter and more humid conditions that have become common in its San Diego habitat.

Sheela Turbek, a postdoctoral researcher in CSU’s Department of Biology, led this study, which was first published Monday in the journal Nature Climate Change. Her team sequenced the genomes of Willow Flycatchers spanning a 100-plus year period, comparing DNA from museum specimens from the late 1800s to modern samples taken today.

“We used over 200 contemporary samples from the Willow Flycatcher to scan the genetic material for specific regions of the genome associated with important environmental variables,” Turbek said. “This includes things like monthly precipitation and monthly maximum temperature. Once we identified regions of the DNA likely involved in climate adaptation, we extracted the genetic information from those regions in both our historical and our modern San Diego samples.”

Proving genetic adaptation over time

Turbek, who is a part of Kristen Ruegg’s lab at CSU, picked up this research as a continuation of a similar project that had been around for 10 years.  The technology needed to sequence whole genomes from historical specimens advanced significantly over the 2010s, making this work possible today.

Turbek focused on the Southwestern Willow Flycatcher because of its endangered status. Ruegg’s foundation of preliminary research showed the birds had locally adapted to different climate conditions across space.

“The Willow Flycatcher is made up of four different subspecies, and the subspecies in the Southwest has faced really precipitous population declines and was listed as federally endangered in 1995,” said Turbek. “There’s a lot of interest from government agencies to effectively manage this subspecies and save it from climate-induced extinction, which Kristen has demonstrated it could potentially suffer from in the future.”

To prove genetic adaptation over time is much more complicated.

Decades-old samples often contain degraded, contaminated or low-yield DNA, which is why, until now, it has been difficult to prove genetic adaptation to an appropriate degree of certainty.

“Museums often send us a little clipping from a toe pad that often has really low DNA concentrations so it’s hard to acquire enough reads of the DNA to have a good idea of what the genetic code looks like,” Turbek said. 

After the years-long effort of sequencing the historical genome, and comparing the historical results to modern samples, the researchers determined that the Willow Flycatcher has experienced an increase in genetic variation over time.

“We think that it was actually mixing or gene flow into the population from neighboring populations that helped recover the gene pool of the Willow Flycatchers in the San Diego area,” Ruegg said. 

Validating predictions of climate change effects

Turbek and Ruegg are excited to be able to validate scientists’ predictions of how some species will adapt to climate change.

“Human-induced climate change is having a drastic effect on the reproductive activities of many species, and is going to drive many organisms to the brink of extinction,”  Turbek said. “The fact that we can document this amount of adaptation over a century-long time scale is somewhat encouraging in that these birds seem to be responding to the amount of climate change that has already occurred. It can help us better predict what’s going to happen in the future, and how species might respond.”