A tinamou in Patagonia, Argentina. Tinamous are ground-dwelling birds that also fly, and they played a pivotal role in Scott V. Edwards' study. GETTY IMAGES PHOTO

Bird biologist explains the history of feathers and flight

By Casandra Martoccia

BAR HARBOR—How did birds acquire feathers and why did some birds like ostriches, emus and kiwis lose the ability to flyOne way to address these questions, said Scott V. Edwards, professor of organismic and evolutionary biology at Harvard’s Museum of Comparative Zoology, is to use comparative genomics, a mapping technology that allows scientists to map genes that code for specific traits.  

This technology can precisely identify where a particular gene or genetic marker is located for evolutionary traits that are liable to change, said Edwards in the keynote address at the 48th annual Maine Biological and Medical Sciences Symposium at the Mount Desert Island Biological Laboratory.  

To predict what is driving the evolution of feathers, Edwards analyzed patterns of emergence that not only are conserved across species but also regulate which genes are expressed as traits. Edwards assembled a database of 13,000 genetic markers responsible for feather development since those markers are also likely involved in the origin of feathers.  

From evidence in the fossil record, scientists know that feathers arose 220 million years ago in nonflying dinosaurs and that the genes involved in the development of feathers are much older.  

This suggests that regulatory innovations arose before the origin of feathers and makes one think more about what is driving the evolution of feathers. 

Edwards then shifted from talking about how a trait like feathers is acquired to how a trait like the ability to fly may be lost. He studied a group of flightless birds that includes ostriches, emus, kiwis and the anomaly birds, tinamous, which are ground-dwelling birds found in the tropics. Tinamous do fly, and they played a pivotal role in his study. 

Researchers previously assumed tinamous were the outlier of the flightless group Edwards studied. However, when these birds are not placed as an outlier, they land in the middle of the evolutionary lineage of flightless birds. This suggests, said Edwards, that flight has been lost multiple times within this group since it was regained in tinamous and then lost again. 

While many scientists think this is implausible, under certain circumstances, explained Edwards, it is relatively easy to lose flight and it is common in many other groups of birds. If we acknowledge that the rate of gaining flight is low and the loss of flight is high, said Edwards, loss of flight becomes expected—a conclusion that could predict the loss of flight in birds in Edwards’ study. 

Edwards compared the genetic makeup of each species in his group of birds while taking into account the order in which they evolved. Once this was complete, he looked at 30,000 genetic markers and analyzed where they were present in the target lineage of birds that cannot fly and the nontarget lineage of the tinamous that can fly. 

Most studies link these two targets, said Edwards, but linking the targets yields false positive genetic markers that accelerate in both the target and nontarget lineages. Edwards found not only a number of genes in flightless birds that target skeletal regulation and bird size—both factors that impact a bird’s ability to fly—but also 42 genetic markers that are now accelerating his search for the genetic element responsible for flightless birds. 

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