Genetic analysis shows that for some Caribbean birds, family is surprisingly far-flung

March 16, 2021

An extinct Haitian bird has a puzzling family tree. (Unsplash/Rural Explorer)

When it comes to identifying birds, DNA always beats binoculars and field guides.

In a study published March 16 in Biology Letters, researchers analyzed the DNA of a toe bone from the Haitian Cave-rail, an extinct flightless bird native to the island of Hispaniola, and found that it is actually not a member of the rail family at all. In fact, some of its relatives are not even from the Americas, but Africa and New Guinea, suggesting that Caribbean bird populations may not have the origins scientists once assumed. 

"A goal of this paper was to put this extinct bird in an evolutionary context, so that we could understand how it evolved with respect to living birds," said coauthor David W. Steadman, curator of ornithology at the Florida Museum of Natural History. "We found that even though this extinct flightless bird had been regarded as a rail, and based on anatomy looks like a rail, the anatomy was masking pretty significant changes in the DNA."

Ornithologists had always taken for granted that this bird, from the extinct Nesotrochis genus, was a member of the flightless Rallidae family because of its appearance alone. It simply looked like one: large legs, small wings, roughly one foot tall, about the size of a chicken. But DNA analysis conducted by Steadman and his colleagues shows that this ex-rail is related to two other species: the extinct azdebills of New Zealand, and the mysterious flufftails, which are still scurrying around swamps and forest floors of Africa and New Guinea. 

Ironically, the Haitian Cave-rail resembles neither adzebills, which were three feet tall and bore huge beaks, nor flufftails, which bear some similarities but are less than half the size of the Haitian Cave-rail, plus difficult to study, according to Steadman.

"To have a big extinct bird in New Zealand be closely related to birds that are in New Guinea and Africa — OK, that's a bit of a surprise," Steadman told The Academic Times in an interview. "But then throw in a Caribbean island, and now we're not only spread across a lot of the old world, they're now in the new world, which means at some point these things crossed the Atlantic."

The ancestor of the Haitian Cave-rail may have crossed the Atlantic Ocean in the early Miocene period, about 20 million years ago, when many species moved from Eurasia to the Americas. It is possible, according to Steadman, that some of them traveled across oceans with stronger currents than today. But that theory remains a hypothesis, and scientists do not know why this dispersion occurred.

When the cave-rail ancestor landed in the Caribbean, it found the paradise that may have robbed it of flight. Islands were ideal avian ecosystems before humans, or any mammals, for that matter. Life was simple with very few or no predators around. Over time, it's possible that natural selection may have favored being a ground-dweller. 

While scientists do not know how long it could take for a bird to become flightless, prior research suggests that 500,000 years may be enough, according to Steadman. 

The Haitian Cave-rail probably died out in prehistoric times, but one of its relatives, the Antillean Cave-rail, also from the Nesotrochis genus, became one of many flightless bird species that stood no chance of survival when European explorers arrived at the Greater Antilles with pigs, dogs, rats and cats, all eager to hunt down these vulnerable birds and their nests.  

In future research, Steadman plans to continue studying the bones of the Nesotrochis genus, comparing them to the birds scientists thought they were related to, as well as their newly discovered family members, to try to see if they may share any further anatomical similarities. After uncovering this genetic one, Steadman says he would be "shocked" if other species didn't have similarly far-reaching backgrounds.

"The birds you see alive today, or ones that went extinct fairly recently, it's a mistake to think that their evolutionary history is based on the continents that surround the Caribbean," Steadman said. "It's really opened up a much broader geographic perspective for understanding the evolution of birds in the Caribbean — your nearest relative doesn't have to be your nearest neighbor."

The study, "Ancient DNA from the extinct Haitian Cave-rail (Nesotrochis steganinos) suggests a biogeographic connection between the Caribbean and Old world," published March 16 in Biology Letters, was authored by Jessica A. Oswald, University of Nevada, Reno and Florida Museum of Natural History; Ryan S. Terrill, Occidental College; Brian J. Stucky, Michelle J. LeFebre, David W. Steadman and Robert P. Guralnick, Florida Museum of Natural History; and Julie M. Allen, University of Nevada, Reno and University of Illinois Urbana-Champaign.

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