image: African glossy starlings change color more than 10 times faster than their ancestors and even their modern relatives, according to researchers at The University of Akron and Columbia University. And these relatively rapid changes have led to new species of birds with color combinations previously unseen, according to the study funded in part by the National Science Foundation and published today in the Proceedings of the National Academy of Sciences USA. view more
Credit: Dustin Rubenstein, Columbia University
AKRON, OHIO, June 10, 2013 – It's not going to happen while you're peering through your binoculars, but African glossy starlings change color more than 10 times faster than their ancestors and even their modern relatives, according to researchers at The University of Akron and Columbia University. And these relatively rapid changes have led to new species of birds with color combinations previously unseen, according to the study funded in part by the National Science Foundation and published today in the Proceedings of the National Academy of Sciences USA.
"Many people enjoy bird watching because all of the different, beautiful colors of feathers, but this study gives us a closer look into the story of how these colors came to be, and how they changed over their millions of years of evolution," said Rafael Maia, the study's lead author and a graduate student in the Integrated Bioscience program at UA.
Just like bar cruisers who don flashy clothes before a night out, birds use feathers to attract the opposite sex and intimidate the competition.
"The feathers aren't just there for flying," Maia said.
The team of scientists used analysis of microscopic feather structures, spectral color analysis, and evolutionary modeling to analyze patterns of evolution in African starlings, a diverse group of primarily brightly colored birds known for their metallic sheens. (By comparison, the European starling – the only starling found in the United States – is a drab creature.)
The researchers focused mainly on the different forms of feather melanosomes, the parts of cells (organelles) that carry the dark pigment melanin. Melanosomes are found in all vertebrates and most typically show up as black, brown or gray. But in birds, melanosomes are sometimes organized in a way that interacts especially with light to create colorful, metallic, and often iridescent feathers. The melanosomes of the African starling groups evolved to become especially suited to react with light of various wavelengths, according to the researchers.
The ancestors of today's starlings reached Africa about 17 million years ago and back then most likely had simple, rod-like melanosomes that are found in most bird species, according to the study. As the ancient starlings of Africa started to split into new species, new melanosome types began to emerge. Some species retained the ancestral rods, while others shed them for one of three unusual forms of melanosomes: hollow rods, solid flattened rods, and hollow flattened rods.
Some of the nearly 10,000 species of birds in the world also have some of these modified melanosomes, but – as a group – African starlings are the only birds to have all four types among them.
"With the appearance of these new shapes comes new ways of interacting with light, and a whole range of colors that these birds could never have made before can now be produced in their feathers," said Maia.
These African Starlings didn't just leave their simple bland relatives behind slowly. When they took on the new melanosome types, they began to sport spiffier plumage more than 10 times faster than their kin.
"Evolving these new melanosomes was like inventing the wheel for these birds—it allowed starlings to reach new colors at an incredibly fast rate" said Matt Shawkey, co-author of the study and UA associate professor of biology and integrated bioscience.
Similar key evolutionary patterns have been found in the jaws of African fishes and the beaks of finches that allow them to adapt rapidly to explore new food sources. But it's not quite the same, the researchers said.
"Bright colors don't help you get a meal – and they certainly don't help hide you from a predator," said Shawkey.
"Feather coloration is very important in African starlings because it is used to signal quality and dominance when competing for mates," said study co-author Dustin Rubenstein, assistant professor in the Department of Ecology, Evolution and Environmental Biology at Columbia University in New York. They help establish dominance and rank in females and males, an earlier Rubenstein study showed.
"And since birds of a feather flock together and all that," said Shawkey, new colors may enable new social groups to form quickly and halt breeding with the rest of the population. Alternatively, bird populations may diverge because of physical barriers such as mountains, and new colors may help keep them separated when the two populations meet again. Either of these processes could lead to the birth of a new species, and may explain why the more colorful starlings, with modified melanosomes and their fast-evolving color palette, also form new species more readily.
"Like some other classic evolutionary innovations, these elaborate ornaments seem to have promoted diversification at a relatively fast rate. However, they do so not by allowing you to eat something new, but just by changing your look." says Maia.
The study was supported by the National Science Foundation, Human Frontiers Science Program, Columbia University, Sigma Xi, the American Museum of Natural History and The University of Akron.
About The University of Akron
The University of Akron offers more than 300 associate, bachelor's, master's, doctorate and law degree programs – with accreditations by 35 professional agencies. With nearly 30,000 students and $65 million in research expenditures, UA is among the nation's strongest public universities focused on innovation, entrepreneurship, and investment in community and economic growth. Programs are targeted to diverse groups of learners, including full-time, part-time and online students, veterans and adults returning to the classroom. The distinctive Akron Experience enhances postgraduate success through internships and co-ops, academic research (both undergraduate and graduate), study abroad, on-campus student employment and service projects.
About Columbia University
Among the world's leading research universities, Columbia University in the City of New York continuously seeks to advance the frontiers of scholarship and foster a campus community deeply engaged in the complex issues of our time through teaching, research, patient care and public service. The University is comprised of 16 undergraduate, graduate and professional schools, and four affiliated colleges and seminaries in Manhattan, and a wide array of research institutes and global centers around the world. More than 40,000 students, award-winning faculty and professional staff define the University's underlying values and commitment to pursuing new knowledge and educating informed, engaged citizens. Founded in 1754 as King's College, Columbia is the fifth oldest institution of higher learning in the United States.
Journal
Proceedings of the National Academy of Sciences