The Pink-throated Brilliant hummingbird, Sunflower gularis, has, as expected, a bright pink neck. So does its cousin, the brilliant-webbed hummingbird, Heliodoxa branickii. When scientists found a Sunshine hummingbird with a glittering golden neck, they thought they might have found a new species. DNA revealed a different story: the golden-throated bird was a never-before-documented hybrid of the two pink-throated species.
John Bates, the senior author of a new study in the journal Royal Society Open Science that reports on the hybrid, first encountered the unusual bird while doing field research in Peru’s Cordillera Azul National Park, which protects an outer ridge on the eastern slopes of the Andes mountains. Since the area is isolated, it would make sense for a genetically distinct population to occur there. “I looked at the bird and said to myself, ‘This thing is like nothing else.’ My first thought was that it was a new species,” says Bates, curator of birds at Chicago’s Field Museum.
But when Bates and his colleagues collected more data on the sample at the Field Museum’s Pritzker DNA Lab, the results surprised everyone. “We thought it would be genetically distinct, but it matched Heliodoxa branickii in some indicators, one of the pink hummingbirds from that general area of Peru,” says Bates. If it was H. branickii, it made no sense for the bird to have golden neck feathers. in the hummingbird family, it is rare for members of the same species to have dramatically different throat colors.
The initial run of DNA sequencing looked at mitochondrial DNA, a type of genetic material that is passed down only through the mother. This mitochondrial DNA gave a clear matching result H. branickii; The researchers then analyzed the bird’s nuclear DNA, which includes contributions from both parents. This time, the DNA showed similarities in both H. branickii and his cousin, X. gularis. It wasn’t half of it branickii and half gularishowever — one of its ancestors must have been half-half, and then later generations mated with more branickii birds.
The question remained how two species of pink necked birds could produce a hybrid without a pink neck. The study’s first author, Field Museum senior research scientist Chad Eliason, says the answer lies in the complex ways in which iridescent feather colors are determined.
“It’s a bit like cooking: if you mix salt and water, you know what you’re going to get, but mixing two complex recipes together can produce more unpredictable results,” says Eliason. “This hybrid is a combination of two complex recipes for a feather from its two parent species.”
Feathers get their primary color from pigment, such as melanin (black) and carotidoids (red and yellow). But the structure of feather cells and the way light bounces off them can also produce something called structural color. Color-changing iridescence is a result of structural color.
The researchers used an electron microscope to examine the structure of the neck feathers at the subcellular level and an analytical technique called spectroscopy to measure how light bounces off the feathers to produce different colors. They found subtle differences in the origin of the parents’ colors, which explain why their hybrid offspring produced a completely different color.
“There’s more than one way to make iridescent magenta,” says Eliason. “The parent species each have their own way of making magenta, and that’s, I think, why you can get that non-linear or surprising effect when you mix those two recipes to produce a feather color.”
While this study helps explain the strange coloration of an unusual bird, researchers say it opens the door to more questions about hybridization.
Distinct species are generally defined as being genetically distinct and not interbreeding. hybrids break this rule. Sometimes hybrids are oddly solitary or sterile, like mules. In other cases, hybrids can form new species. It’s not clear how common hummingbird hybrids like the one in this study are, but the researchers speculate that hybrids like this may contribute to the variety of structural colors found in the hummingbird family tree.
“Based on the speed of color evolution seen in hummingbirds, we estimated that it would take 6-10 million years for this drastic rose-gold color change to evolve in a single species,” says Eliason.
Co-author Mark Hauber at the University of Illinois Urbana-Champaign adds that “this study gives us evidence for the nanostructural basis of evolutionary changes in color.”
Bates and Eliason’s Field Museum colleagues Jacob Cooper (now at the University of Kansas), Shannon Hackett, Erica Zahnle, Dylan Maddox, and Taylor Hains, as well as Tatiana Paqueño Saco (Peruvian Ministry of Natural Resources) and Mark Hauber contributed to this study. (University of Illinois, Urbana-Champaign).