The breeding of two distinct parent species gave rise to a new lineage (termed “Big Bird” by the researchers). This lineage has been determined to be a new species. This image is of a member of the Big Bird lineage. Photo: P.R. Grant, Princeton University

A pair of Princeton University researchers, in collaboration with Uppsala University, report that interbreeding among species can produce new species within just two generations.

The evidence resides in a new bird lineage termed “Big Bird”, which was produced by two species on the Galápagos Islands – one native to the islands, the other an “immigrant” bird.

The remote Galápagos Islands, home to Darwin’s famous finches, have provided researchers with ideal opportunities to study evolution and adaption for decades.

B. Rosemary Grant and Peter Grant, a wife-and-husband duo of scientists from Princeton, have been conducting field work on Darwin’s finches for the last 40 years.

In 1981, a graduate student working with the Grants observed a unique bird on the island of Daphne Major, and noted that its physical appearance, as well as its song, were vastly different than the three resident species known to the island.

The bird had a much larger body and beak size, and sang a distinct song.

The team took a blood sample and released the bird. But later, it mated with a resident medium ground finch of the species Geospiz fortis, sparking the introduction of a new lineage.

The Grants followed the new lineage, which they refer to as “Big Bird lineage”, for six generations. They took blood samples each time to use for genetic analysis.

For the latest round of research, researchers from Uppsala University analyzed the DNA obtained from the parent birds and their offspring. They determined that the original “immigrant” male parent was a large cactus finch of the species Geospiza conirostris from Española island, located more than 62 miles southeast of Daphne Major.

This discovery shows that the male finch couldn’t return home to mate with his own species, so he adapted a “Plan B” of sorts by choosing a mate from one of the three native species on Daphne Major.

However, the different look and unusual mating call of the offspring failed to woo any resident female birds, prompting the offspring to make with members of their own lineage. Despite the intense inbreeding, the development of the new species continued to flourish.

Now, the new species is made up of 30 individual birds.

“The novelty of this study is that we can follow the emergence of new species in the wild,” said B. Rosemary Grant, a senior research biologist, emeritus, and a senior biologist in the Department of Ecology and Evolutionary Biology. “Through our work on Daphne Major, we were able to observe the pairing up of two birds from different species and then follow what happened to see how speciation occurred.”

The formation of the new species only took two generations, bucking previous assumptions that the emergence of a new species in the wild takes much longer.

“We have no indication about the long-term survival of the Big Bird lineage, but it has the potential to become a success, and it provides a beautiful example of one way in which speciation occurs,” said Leif Andersson, a professor at Uppsala University. “Charles Darwin would have been excited to read this paper.”

The findings were published in Science.