For the second time in 10 months, scientists are rewriting the evolutionary history of the world’s birds.
Last December, a team of more than 100 researchers used genetic data from 48 modern bird species to produce the most comprehensive avian family tree ever published. Erich Jarvis, a neurobiologist at Duke University Medical Center, and his colleagues described their findings in one of 28 papers on bird evolution that were published nearly simultaneously as part of the sweeping Avian Phylogenomics Project.
Today, Richard Prum, the William Robertson Coe Professor of Ornithology at Yale University, and six other scientists from Yale, Cornell, and Florida State universities report in the journal Nature that they analyzed the genomes of 198 living bird species, representing all major bird lineages, and produced a family tree that is significantly different from Jarvis’s.
Prum’s approach studied four times as many species. Moreover, Gavin H. Thomas, an expert on the phylogenetics of birds at the University of Sheffield, notes in an accompanying analysis that the study sampled genomes “both deeply (the number of nucleotides sequenced) and broadly (the number of species).”
More than 90 percent of modern birds are part of the clade known as Neoaves. In other words, they are believed to have evolved from a common ancestor. The few orders of birds not among the Neoaves are the ostriches and kiwis (Palaeognathae); chickens, grouse, and other landfowl (Galliformes); and ducks and geese (Anseriformes).
Prum’s team says it identified five major groups within Neoaves:
Strisores — nightjars, frogmouths, and other nocturnal birds, along with diurnal swifts and hummingbirds.
Columbaves — turacos, bustards, cuckoos, pigeons, sandgrouse, and mesites.
Gruiformes — cranes, rails, crakes, Sungrebe, flufftails, and others.
Aequorlitornithes — shorebirds, flamingos, grebes, gulls, tropicbirds, penguins, and other waterbirds.
Inopinaves — all landbirds, including hawks, owls, toucans, falcons, parrots, and songbirds.
South America’s enigmatic Hoatzin, Prum writes, is a sister to all other landbirds, and its genus, Opisthocomus, at about 64 million years of age, “is the most ancient bird lineage consisting of only a single, extant species.”
The new analysis does not support Jarvis’s suggestion that Neoaves can be divided into two groups, known as Columbea and Passerea.
“This is the first study to analyze hundreds of genetic loci (or ‘genes’) from hundreds of species,” Prum says. “We find that when we reach that threshold, we can resolve even the very short, early branches in the avian phylogeny with real confidence. Plus, we find new relationships that are well supported. Who could have imagined that bustards are related to cuckoos?”
He notes that the Jarvis study also reported a bustard-cuckoo relationship, but its conclusion was less confident. The finding, he says, “is a substantial discovery.”
Thomas, of the University of Sheffield, writes that the evolutionary relationships uncovered by Prum “produce a pattern akin to tangled roots, rather than a tree.”
Prum’s findings correspond with Jarvis’s interpretation that birds evolved rapidly for about 15 million years beginning around 65 million years ago — about the same time that most dinosaurs disappeared, an event known as the Cretaceous–Palaeogene (K–Pg) mass extinction.
“Our data imply that the Neoavian orders and families began to radiate rapidly soon after the K-Pg,” Prum says.
But he says it’s not clear that the extinction opened up ecological niches that birds were able to fill. “There are plenty of later explosive radiations that were not associated with extinction events, like the passerine birds or waterbirds,” he notes. “So I would not claim that we know why that radiation happened.”
Prum’s study also confirms the fascinating evolutionary relationships of landbirds that Jarvis’s and other recent studies have found: that all of today’s landbirds — songbirds, woodpecker, toucans, parrots, you name it — likely evolved from a raptor-like ancestor.
This doesn’t mean that songbirds evolved from hawks or that today’s hawks look like their raptorial ancestors, Prum says. What it suggests is that while all landbirds are related, modern hawks, owls, falcons, and seriemas never lost the predatory diet of the raptors that they evolved from.
Jacob Berv, a Ph.D. student at Cornell and a co-author of the study, says it provides a basis that other researchers can use to “flesh out the evolutionary relationships among more contemporary groups of birds. We hope that this will allow scientists to test hypotheses about avian evolution in a phylogenetic context that is robustly supported — something that we never before had the ability to do.”
The situation is similar, he says, to trying to decipher an out-of-focus photo. “The evolutionary events surrounding the Cretaceous-Palaeogene mass extinction happened so quickly that the genetic signature of these events have been extremely difficult to discover. Our results provide us with a picture that, while possibly incomplete, is in much sharper focus.”
Understanding the deep evolutionary relationships of birds is vitally important, Berv adds.
“Living birds have a very long and complex history,” he says. “Any attempt to understand their biology at a broad scale requires an understanding of this deep historical context. It’s critical to every area of bird biology. How they act, where they live, what they look like, how they communicate — it’s all linked to how they evolved in relation to each other.” — Matt Mendenhall, Managing Editor
Read the abstract
Richard O. Prum, Jacob S. Berv, Alex Dornburg, Daniel J. Field, Jeffrey P. Townsend, Emily Moriarty Lemmon, and Alan R. Lemmon. A comprehensive phylogeny of birds (Aves) using targeted next-generation DNA sequencing. Nature (2015). Abstract.
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