The Strange Origin of a Manakin’s Golden Crown
Posted January 3, 2018 5:33 p.m. EST
Three related species of manakins occupy adjacent parcels of the Amazon rain forest: Opal-crowned, snow-capped and golden-crowned. They are all plump like sparrows, small enough to cup in a hand and have radiant yellow-green upper bodies with golden undersides.
Biologists are now unlocking the mystery of how these neighboring birds became distinct species. Last week, a team of scientists confirmed in Proceedings of the National Academy of Sciences that the golden-crowned manakin is a unique hybrid species that emerged from a cross between the opal-crowned and snow-capped manakins about 180,000 years ago.
Though one-off mating events between different species occur across the animal kingdom — think pizzly bears, occasional crosses between polar and grizzly bears — the establishment of an entirely separate hybrid species is thought to be relatively rare.
For a new species to occur, it has to become reproductively isolated, or form a stable population that no longer freely mixes with its parent species, said Alfredo Barrera-Guzmán, who led the new research as a doctoral student at the University of Toronto Scarborough.
Opal-crowned manakins wear an iridescent toupee, evocative of a unicorn’s mane. Snow-capped manakins are topped with bright glacial patches. And members of the hybrid species, the golden-crowned manakin, display a burst of yellow to match their bellies. Choosy females prefer the particular color sported by males of their own species, leading to reproductive isolation.
Hybrids often look like an intermediate between their parent species, which made scientists skeptical that you’d get a golden-crowned manakin by crossing opal-crowned and snow-capped manakins.
To settle the mystery, Barrera-Guzmán and his colleagues sequenced much of the golden-crowned manakin’s genome and confirmed that it has a blend of DNA from the other two species.
The scientists then examined feathers from the heads of golden-crowned males under an electron microscope. They found that the manakin’s warm crown comes from pigments called carotenoids, which the birds get from their diet. When chemically stripped of these pigments, the feathers turned grayish-white.
Barrera-Guzmán’s team suspects that the first male mixes between snow-capped and opal-crowned manakins bore this dull tuft, an intermediate between the white and iridescent caps of their forebears.
During the last ice age, the Amazon rain forest shrunk and possibly cut some hybrids off from their parent species — the golden-crowned manakin’s habitat today is separated from snow-capped and opal-crowned territories by rivers and mountains.
As the hybrids evolved in this segregated space, females may have preferred to mate with males that had a higher concentration of carotenoids in their crown, producing an attractive yellow blaze, said Jason Weir, an associate professor of evolutionary biology at the University of Toronto Scarborough and senior author of the new paper.
Hybridization is sometimes seen as reducing biodiversity, because it can merge distinct species together. But as genetic sequencing improves, scientists will likely discover more instances of hybridization generating new life-forms. Just this fall, scientists announced the discovery of a hybrid finch in the Galápagos that is in the process of becoming a new species.
“Hybridization is a double-edged sword,” Weir said. “It can erode diversity, but it can also be a creative force.” In the case of the golden-crowned manakin, it even created a new head of gold.