春水堂视频

A new large-scale study from CU Boulder and colleagues provides first evidence that a gargantuan, inhospitable plateau in Asia maintains the species barriers of some birds鈥�

In the middle of Asia, there is a vast, high-altitude desert that not only helped shape the evolution of barn swallows鈥攁nd likely other birds, too鈥攂ut continues to keep them distinct by altering migration paths, according to new research from the University of Colorado Boulder.

These new findings, , provide the most-convincing evidence yet for a long-held hypothesis that the Tibetan plateau is an important catalyst and maintainer of the vast diversity of birds found in Asia. It does this by being a barrier that keeps them separate, sending some migrating birds to Africa and others to south and southeast Asia.

鈥淲hat we鈥檙e getting is a really consistent snapshot that different subspecies (of barn swallows), when they come together, are responding in the same way to a major geographic barrier,鈥� said Rebecca Safran, an associate professor of ecology and evolutionary biology at the University of Colorado Boulder and a senior听author on the paper.

鈥淚t suggests that there鈥檚 something universal about that place on planet Earth that at least different subspecies of barn swallows are responding to by migrating in different directions above it.鈥�

The Tibetan plateau, which is also known in China as the Qinghai-Tibet Plateau, the Qing-Zang Plateau or the Himalayan Plateau, is the third least-populous place on earth鈥攐nly surpassed by Antarctica and northern Greenland. Bordered by mountain ranges like the Himalayas and deserts like the Gobi, it鈥檚 a gigantic, inhospitable place for humans. For birds, it can be downright impassable.

For over a decade, it鈥檚 been hypothesized that because it鈥檚 so treacherous, it might be influencing bird migration and speciation鈥攐r the formation of new species鈥攊n Siberia and central Asia. Because it鈥檚 impassible, smaller birds just don鈥檛. They go around to either south or southeast Asia or they go west towards the Middle East and Africa.

But that hypothesis hadn鈥檛 been clearly supported鈥攗ntil now.

Researchers from CU Boulder and institutions from across Asia, with the help of a National Science Foundation CAREER grant funded to Safran, initially went to Asia to look at whether geographic barriers like the Tibetan Plateau played any role in keeping subspecies, or different members of the same evolutionary family (species), genetically distinct.

To do that, they looked at a familiar species found nesting on human structures across the northern hemisphere: barn swallows.

These birds are a great species to study speciation, according to the researchers, because of their relatively recent divergence from one another that has created a vast amount of variation in characteristics like appearance or migration paths.

In Asia alone, there are three different subspecies, and so the researchers, led and organized by Liz Scordato, a former postdoctoral researcher at CU Boulder and the study鈥檚 lead author, set out to study where these species collided. They traveled to Asia three times during the summer between 2013 and 2015 and collected samples from 1,288 barn swallows across Siberia, China, Japan and Mongolia.

The samples鈥攚hich included the color of feathers on the breast and throat of the bird, the length of the tail feathers, the carbon isotope value (an environmental signal that can make its way into cells) of tail feathers, and the length, pointedness and curvature of the wings鈥攏ot only established which species they were handling, but also where they might have migrated that past winter.

What they found as they lined up the species maps and their subsequent hybrid zones is that, while they don鈥檛 have evidence that the birds actively avoid the Tibetan Plateau, it does appear to still keep them genetically distinct.

And they don鈥檛 think barn swallows are the only bird in which this might be the case.

鈥淏arn swallows are really sort of the perfect test case, but we think that this is good evidence that this is sort of a general barrier that affects lots of different bird species,鈥� said Scordato, who is now an assistant professor at Cal Poly Pomona.

Safran agreed. 鈥淭his is not just a barn swallow story.鈥�

This study is the result of a cross-global effort that involved collaborators from Russia, China, Mongolia and Japan. The other researchers include Chris C.R. Smith, Georgy A. Semenov, Yu Liu, Matthew R. Wilkins, Wei Liang, Alexander Rubtsov, Gomboobaatar Sundev, Kazuo Koyama, Sheela P. Turbek, Michael B. Wunder and Craig A. Stricker.

鈥淲e鈥檙e not out in the forest doing this work. We鈥檙e going from village to village and town to town looking for these birds,鈥� said Scordato.

鈥淲hat that meant was that we had to talk to people the whole way and explain to them who we were and what we were doing and ask if we could go into their houses and catch their birds, and so the project absolutely would not have been possible without really amazing, local collaborators.鈥�