How An Icon of Evolution Lost Its Flight

2017-06-06T16:35:48+00:00 June 6, 2017|
Scientists have discovered some of the genetic changes behind the useless wings of the Galapagos cormorant. (Credit: Charles J Sharp)

(Click to enlarge) Scientists have discovered some of the genetic changes behind the useless wings of the Galapagos cormorant. (Credit: Charles J Sharp)

In 1835, the Galapagos Islands shaped the thoughts of a young British naturalist named Charles Darwin, and helped inspire his world-shaking theory of evolution. For that reason, the islands have become something of a Mecca for biologists, who travel there to see the same odd creatures that enthused Darwin.

(From the Atlantic / by Ed Yong) — “I like seeing wildlife in general, but some of these creatures have become iconic in evolutionary biology,” says Leonid Kruglyak from the University of California, Los Angeles, who visited the Galapagos in 2012. The famous finches, with their well-adapted and variously shaped beaks, are especially famous, but Kruglyak found them underwhelming. He was more drawn to the flightless cormorants.

There are around 40 species of these birds in the world, and all but one of them can fly. The sole exception lives on the Galapagos, and can be seen on the coasts of the Isabela and Fernandina islands, drying its shriveled and tatty wings in the sun. Compared to other cormorants, this one is about 60 percent bigger. Its wings are smaller and its feathers shorter. Its breast muscles, which would normally power a flapping stroke, are smaller, and the part of the breastbone that anchors those muscles is stubbier.

Kruglyak wanted to know why this bird couldn’t take to the skies. Specifically, as a geneticist, he wanted to know what genetic changes had grounded it. When he got back to his lab, he reached out to a research team that had collected blood samples from 223 flightless cormorants—almost a quarter of the total endangered population. He and his own team used these samples to sequence the cormorant’s genome, then compared its DNA to that of three other cormorant species, looking for mutations that are unique to the flightless one, and that are likely to alter its genes in important ways.

They found a long list of affected genes. Many of these, when mutated in humans, distort the growth of limbs, resulting in extra fingers, missing digits, and other similar conditions. Some of them are also responsible for a group of rare inherited disorders called ciliopathies, where cilia—small hair-like structures on the surface of cells—don’t develop correctly. Cells use cilia to exchange signals and coordinate their growth. If these hairs don’t form correctly, many body parts don’t develop in the usual way. In particular, some people with ciliopathies grow up with short limbs and small ribcages—a striking parallel with the stunted wings and small breastbone of the flightless cormorant.

Read the full article here: