Biologist gains insights into evolution of birds
Lincoln, Neb., December 11th, 2014 — A University of Nebraska-Lincoln researcher has contributed to discoveries about bird evolution as part of a new study that sequenced the complete genomes of 45 avian species.
Published Dec. 11 in the journal Science, the study found that avian genomes — the complete archive of genetic material present in cells — have exhibited surprisingly slow rates of evolution when compared with their mammalian counterparts.
Jay Storz, a Susan J. Rosowski Associate Professor of Biological Sciences, led a research group that assisted the study by examining the evolution of multi-gene families shared by birds and mammals. Each family comprises a collection of genes related to one another through a history of duplication, with all members of a given family descending from a single ancient gene.
Storz and his colleagues used computational methods to measure "gene turnover," the rate at which genes are gained or lost over time. The researchers reported that the rate of turnover in avian gene families is roughly two times slower than in mammals. This finding reflects a larger-scale pattern of evolutionary stasis in avian genomes, according to Storz.
"In mammals, there's this continual turnover — it's like a genomic turnstile. With birds, it's far more conservative," Storz said. "There might be a gene family that consists of, say, 10 members in the common ancestor of birds and mammals. In mammals, that gene family has probably expanded and contracted in different lineages, and this results in dramatic differences in gene family size and membership composition among contemporary species. In birds, those 10 ancestral gene copies will remain intact and are inherited by all descendant lineages, so very little variation accumulates among species."
The lower rates of gene duplication in birds help account for the fact that avian genomes are typically much smaller and more streamlined than in mammals, Storz said.
Evolutionary biologists have long focused on gene duplication because it represents an important source of "evolutionary innovation," according to Storz. Though duplicated genes initially perform redundant functions, the copies that are retained sometimes adopt new functions or divide up ancestral responsibilities.
"One of the implications of the comparative genomic study is that there may be a reduced scope for evolutionary innovation among birds," he said. "Because there's a comparatively high rate of gene duplication among mammals, there are increased opportunities for these newly produced genes to evolve new functions."
Storz noted that complete genome sequences were previously available for only a few avian species. Adding 45 genomes to the mix, he said, represents an exponential leap in the amount of data available to evolutionary biologists.
"All of a sudden, we have this treasure trove," Storz said. "We were able to make some really informative comparisons because we now have extensive amounts of genomic data for different vertebrate species.
"The availability of these new avian genomes provides opportunities to address questions about the evolution of bird-specific characteristics in ways that weren't possible before."
The study was co-authored by researchers from institutions in Asia, Europe, North America, South America and Australia. Storz's research group included Juan Opazo and Federico Hoffmann, assistant professors at Universidad Austral de Chile and Mississippi State University, respectively.
Opazo and Hoffman formerly served as postdoctoral researchers at Storz's UNL laboratory. The three have also teamed with Chandrasekhar Natarajan, senior research associate of biology at UNL, to publish a new companion study in the journal Molecular Biology and Evolution.
Writer: Scott Schrage, University Communications