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January 24, 2007
University of Nevada, Reno researcher Matthew Forister is among a group of scientists that have documented an unusual type of speciation in the Sierra Nevada, including a hybrid species of butterfly that can trace its lineage as far back as almost a half a million years ago. In a recently published article in the leading research journal Science, the discovery is one of the most convincing cases of this type of species formation that has ever been demonstrated in animals.
"Our genetic work is what really clinched the hybrid angle," said Forister, a research professor in the College of Agriculture, Biotechnology and Natural Resources' Department of Natural Resources and Environmental Science. Forister explained that it has been known that two types of butterflies — Lycaeides melissa and Lycaeides idas — live in the Sierra, with the L. melissa living on the eastern slope of the Sierra and the L. idas living to the west. Forister's team found that a third species of Lycaeides has evolved in the upper alpine reaches of the Sierra.
The team used molecular genetics to show that the "new" species carries genes from both parental species. The scientists estimate that about 440,000 years ago the L. melissa and L. idas came into contact in the Sierra. Their offspring, cut off from the rest of their clan, eventually evolved into a unique and genetically distinct species.
"It's interesting, because the alpine butterflies have wings that look like the butterflies from the eastern Sierra," Forister said. "But their mitochondrial DNA more clearly resembles those from the western Sierra. When you think about all of the changes the world has undergone, and how parental species have moved in response to climate change and have possibly come into contact many times, you realize that the world is a messier place than you first thought.
"Ultimately, what we've studied highlights the importance of natural selection, and the more general idea that we are still learning many of the ways in which species are formed."
Forister's collaborators included UC-Davis professor Arthur Shapiro, Zachariah Gompert and Chris Nice of Texas State University and James Fordyce at the University of Tennessee. Shapiro is one of the world's foremost butterfly experts. Forister did his graduate work at UC-Davis under Shapiro. His graduate work was funded by the National Science Foundation.
The team's findings provide an important piece to the puzzle in the understanding of how animal species emerge. It is widely believed that plant species can be commonly created through such species crossing; hybrid species formation among animals, however, has been much less thoroughly studied.
Forister and his colleagues worked on some of the more barren reaches of the upper alpine in the vicinity of Lake Tahoe, plucking samples of blue (male) and brown (female) butterflies from the rocks and sparse alpine vegetation there. The samples were studied by the research members who worked to analyze the species' DNA in a laboratory in Texas.
"We worked within a very narrow window because these butterflies are at their peak flight for only a few weeks in the middle of the summer," Forister said.
The field work proved to be just as important as the laboratory work, as the team made important findings regarding the new species' adaptive habits. Though the climate is extreme at high elevations and the flying season lasts only a matter of a few weeks, the researchers noted that the still-unnamed species seeks out a certain plant at the higher elevations. They use this host plant to lay their eggs. Their "parent' butterflies of the eastern and western Sierra do not show the same affinity for this particular host plant, the balloonpod milkvetch. This was another critical illustration that a habitat and species shift had occurred.
By understanding how the "new" species lives, the research team is also adding to the scientific-based knowledge that could some day help preserve the butterfly's habitat, Forister added. "Now that we've finished this part of the study, we'd like to turn our attention to some of the other ranges of the West, and investigate similar areas of overlap," Forister said.