Tracing the origin of flightless birds brought together the research efforts of "developmental biologists, computational biologists, morphologists, statisticians, population geneticists--and, of course, ornithologists."
SINCE CHARLES DARWIN'S era, scientists have wondered how flightless birds like emus, ostriches, kiwis, cassowaries, and others are related--and, for decades, the assumption was that they all must share a common ancestor who abandoned the skies for a more grounded life.
By the early 2000s, new research using genetic tools upended that story, and instead pointed to the idea that flightlessness evolved many times throughout history. Left unanswered, however, were questions about whether evolution had pulled similar or different genetic levers in each of those independent avian lineages.
A team of Harvard University researchers believes they may now have part of the answer. Based on an analysis of the genomes of more than a dozen flightless birds, including an extinct moa, the researchers, led by Tim Sackton (director of bioinformatics for the Informatics and Scientific Applications group) and Scott Edwards (professor of organismic and evolutionary biology) found that, while different species show wide variety in the protein-coding portions of their genomes, they appear to turn to the same regulatory pathways when evolving flight loss.
"There is a long history in evolutionary biology of converging traits--the idea that there's independent evolution toward the same kind of phenotype," Sackton explains. "What we were interested in is, how does that happen?'
Flightless birds all have similar body types, Sackton notes. "They have reduced forelimbs [wings], to different degrees, and they all have this loss of the 'keel' in their breastbone that anchors flight muscles. What that amounts to is a suite of convergent morphological changes that led to this similar body plan across all these species."
To understand what drove that suite of changes, Sackton, Edwards, and their colleagues turned to the genomes of the birds themselves. "We wanted to compare not just the parts of the genome that code for proteins, but also the parts of the genome that regulate when those proteins are expressed," Sackton explains.
To identify those regions in the various species examined for the study, the team used a process that involves aligning the genomes of more than three dozen bird species--both flying and flightless--and then identifying regions that...