The True ‘Origin of Species’

Armed with DNA sequencing technology, an A&S researcher is closer than ever to solving the riddle of natural selection.

Albert Uy is a modern-day Darwin. Like his 19th century predecessor, the College of Arts & Sciences biology professor and Aresty Chair in Tropical Ecology spends much of his time on remote islands staring at birds. Uy’s off-campus stomping grounds are the Solomon Islands near Australia, but when we caught up with him on Skype, he was in the Galapagos, site of one of the most famous expeditions in scientific history.

In 1831, a 22-year-old Charles Darwin — medical student, beetle collector and geology buff — joined the crew of the H.M.S. Beagle on a four-year surveying journey to South America. In 1835, while mapping the Galapagos island chain, the young Darwin made a confounding observation about the native wildlife.

Instead of being inhabited by the very same species of bird or tortoise — or very different species, for that matter — each island in the Galapagos chain was home to strikingly similar, but clearly distinct varieties of the same animals.

On the return voyage to England, Darwin brought back several stuffed finches, each with different plumage and beak shape. Over the next decades, Darwin would propose that each of these finch species evolved from a single ancient species that first flew to the island from the mainland. The physical differences in each finch species were the product of different evolutionary pressures on each island. Darwin called his theory natural selection and it turned the scientific world on its head.

More than 175 years after Darwin landed at the Galapagos, Uy says that we still have a lot to learn about how the natural selection process actually works. Where do new species come from? How does evolution work on the molecular level? And how do we pinpoint the precise moment when one species becomes two? Uy believes that a species of bird called the flycatcher on the Solomon Islands may hold the key.

“This is a remarkable example of a bird that is on the verge of becoming another species,” explains Uy, who has received grants from both the National Science Foundation and the National Geographic Society to conduct his research. “Flycatchers are spread all across the Solomon Islands, and as they jump from island to island, the populations start changing. We are using a combination of field observation and molecular tools to understand the bird’s evolutionary history and to test whether they are indeed new species.”

This is where Uy and his team take Darwin’s theory into the 21st century. By collecting blood samples from living flycatchers, Uy’s lab can sequence the DNA of birds that exhibit different physical traits, like beak shape and plumage.

“What we are finding are the unique mutations,” Uy says, “the specific genetic changes that underline the physical changes that are resulting in the creation of a new species.”

Here’s how it works. There are two varieties of flycatcher in the Solomon Islands that are identical in every way except for their color. One is black from head to toe, while the other is called “chestnut-bellied” for its orange-brown vest. Each lives on a separate island. The question is whether the color difference is the expression of a genetic mutation that is driving the two populations apart.

Uy and his team found existing research that identified an all-black gene mutation in mice and dogs. Using DNA sequencing technology, Uy analyzed the same sequence of base pairs of the flycatcher genome across several different wild varieties. Only the all-back birds had the mutation, while the chestnut varieties and others carried the ancestral DNA sequence.

“Not only do we see how natural selection is operating over time, but we’re tracking the genetic changes that are responsible for those population changes,” Uy explains. “Next, we can test whether two populations of flycatchers recognize each other as the same species.”

Uy does this using “taxidermy mounts,” a fancy word for stuffed birds. He’ll introduce a stuffed all-black male into a chestnut-bellied population and see how aggressively the other males react. The more aggressive the behavior, the more likely the birds recognize each other as the same species, and therefore a mating threat. If the chestnut-bellied birds ignore the all-black intruder, Uy says, it strengthens the argument that “a single genetic mutation can create a new species.”

“What we’re really excited about,” Uy says, “and what National Geographic and the NSF are excited about, is the ability to go from the molecules all the way to the population; to understand what Darwin really struggled with, what he called “the mystery of mysteries;” to understand the true ‘origin of species.’”

A portion of Uy’s NSF funding is earmarked to produce a documentary film about his Solomon Islands research. Filming is ongoing through 2013 with hopes of distributing the documentary through networks like PBS or the National Geographic Channel. Uy is also creating a companion website to make the science of natural selection more accessible to the public.

Learn more about the Uy Lab, including an amazing field course for UM undergraduates that Uy is leading to explore speciation and conservation on the Solomon Islands.

August 15, 2013