BATON ROUGE – In a study that sheds light on the origin of bird species in the biologically rich rainforests of South America, LSU Museum of Natural Science Director and Roy Paul Daniels Professor in the Department of Biological Sciences, Robb Brumfield, and an international team of researchers funded by the National Science Foundation, or NSF, published a paper this week challenging the view that speciation – the process by which new species are formed – is directly linked to geological and climatic changes to the landscape.
The researchers, whose findings were published Sept. 10 in the journal Nature, found that the geographic isolation of populations within a single species is more often due to movements of birds across physical barriers, such as mountains and rivers, that occur long after the geological origin of those barriers. Their conclusions not only cast a new light on how the initial step of speciation occurred in tropical birds, but also provide a generalizable explanation for how speciation may be initiated in other regions and in other organisms.
To examine the timing of speciation, the scientists compared genetic patterns among a diverse array of bird lineages that occur in the Neotropics, one of the six major zoogeographical regions of the world extending from Mexico south to the southern most tip of South America known to have more species of birds than anywhere else in the world. Each lineage contained populations situated on the opposite side of large dispersal barriers and, with genetic data, they were able to estimate the time that the populations became isolated from one another. They found that most speciation occurred long after the origin of the Andes and the Amazonian river system.
LSU Museum of Natural Science Director Robb Brumfield is removing tissue from a liquid nitrogen vapor freezer at the Museum of Natural Science.
(Photo Credit: Photo by Samantha Fields.)
"By using detailed sampling of many bird lineages, we were able to get a clearer and larger picture of when and how species formed within those lineages. The extraordinary diversity of birds in South America is usually attributed to big changes in the landscape over geological time, but our study suggests that prolonged periods of landscape stability are more important," said Brumfield. "Our results also suggest that human alterations of the landscape can effectively kill the speciation process. If the path to disperse from point A to point B is erased, then there is no way for the initial step of speciation to occur."
"It is probably only in birds that the genetic sampling is sufficiently dense to examine how interactions between the landscape and birds influence the speciation process," he added.
The thousands of samples used in this study represent the culmination of more than 30 years of field expeditions led by generations of LSU students and scientists, plus similar work done by ornithologists at other research institutions.
Source: Louisiana State University