In uncertain times, it?s nice to think that people band together to help one another.
While the verdict may be out on the human race in this regard, African starlings are a different matter. Some starling species exhibit remarkable cooperative behavior, and a new study shows one factor that has influenced its evolution: climate uncertainty.
The behavior is cooperative breeding, in which some individuals delay their own breeding to help raise the offspring of others, who may or may not be relatives. Among the 45 African starling species, some breed cooperatively and some do not.
Dustin R. Rubenstein, now at the University of California, Berkeley, and Irby J. Lovette of Cornell?s Laboratory of Ornithology undertook a genetic analysis of all 45 species and used it to build a family tree showing evolutionary patterns. Then they used rainfall data, in some cases going back more than 140 years, from across Africa to determine how predictable the weather is in various starling habitats.
Their findings, published in Current Biology, show that cooperative-breeding species largely inhabit semi-arid savannas, where rainfall is highly unpredictable from year to year. In forests, where rainfall was more consistent, noncooperative breeders were more prevalent.
In studying the family trees, the researchers found much evidence that cooperative breeding evolved at various times as starling species moved to savanna habitats. Cooperation would be expected to confer an evolutionary advantage, because in very dry years, when food and other resources are scarce, it helps ensure that more offspring survive.
Source: http://www.nytimes.com/2007/08/21/science/21obstar.html?ref=science