Intensive hunting of the pigeons in the mid-to-late 19th century disrupted their ability to breed, Johnson said. That and habitat destruction led to the bird's eventual extinction. (The last of her kind, a passenger pigeon named Martha, died in the Cincinnati Zoo in 1914.)
To find the passenger pigeon's place in the evolutionary history of pigeons and doves, Johnson and his colleagues compared sequences from two of its mitochondrial genes with those of 78 species of pigeons and doves from around the world. (There are more than 300 species of pigeons and doves worldwide.)
"We had two sequences from the mitochondrial genome, which is a separate organelle in the cell that has its own genome," Johnson said. Mitochondrial genes are plentiful and so are easier to sequence, he said. And the mitochondrial genome evolves more rapidly than the nuclear genome, making it a good target for evolutionary studies.
The researchers first analyzed the available sequence data for all (extant and extinct) pigeons and doves together. Then they focused only on the living species, for which much more genetic information is available. They built a family tree of all living pigeons and doves, and then compared the available gene sequences of the passenger pigeon to those of its relatives to find its place in that tree. Both approaches placed the passenger pigeon on the same place in the tree.
Prior to this study, some believed that the passenger pigeon was most closely related to the mourning dove, a smaller species that also has a relatively long tail, Johnson said.
"But it turns out, based on the DNA, that it's actually related to the New World big pigeons in a totally different genus," he said.
The band-tailed pigeon, Patagioenas fasciata, which lives in the western mountainous regions of North
|Contact: Diana Yates|
University of Illinois at Urbana-Champaign