The findings, published in the January 21 issue of Science magazine, have broad implications for preserving biological diversity and endangered species, says Irwin.
"The process for how one species evolves into two is a subject of intense research interest and debate and is fundamental to understanding diversity of life," says Irwin, who spent ten months between 1994 and 2002 studying greenish warblers in Asia. "Until now, no one has been able to show continuous gene flow between reproductively isolated species via geographically connected populations a process of evolution called 'speciation by distance.'"
Part of the difficulty in proving the theory has been that few examples of such species are known today. The greenish warbler, living throughout Asia, and the Ensatina salamander found in mountains in North America's west coast, are the only known clear examples of species that may have evolved across distance.
Two distinct forms of greenish warblers co-exist in central Siberia but do not interbreed there, making them distinct species in that region. Irwin, along with co-authors Staffan Bensch (Lund University, Sweden), Jessica Irwin (UBC) and Trevor Price (University of Chicago) used a new genetic analysis technique called amplified fragment length polymorphism (AFLP) to trace a genetic gradient from one Siberian species to the other via a long chain of geographically connected populations to the south, surrounding the Tibetan Plateau.