Previous work by members of this team and other collaborators had revealed that an allele -- a variable DNA sequence -- in a gene called phosphoglucose isomerase (Pgi) differed significantly between the old and the new populations. One Pgi allele was associated with two important aspects of metabolism within the butterfly's abdomen and its thorax. First, the new-population, "venture-forth" females were more likely to possess a particular Pgi allele associated with faster egg production. "It's easy to imagine why this kind of ovarian-function trait would provide 'venture-forth' females with an advantage," Marden explained. "Abandoning the secure, known environment can be a perilous endeavor, and life expectancy for such butterflies is probably greatly reduced. Under these conditions, the ability to get a reproductive head start would allow these adventurers to mate earlier, and to fly off to lay their eggs in new habitat patches sooner." Second, the scientists found that the same Pgi allele predominates in females that are better "sprinters," able to fly better for short distances. Marden explained that for those individuals that fly away to colonize new areas, exceptional muscle function could be a more crucial trait than it would be for "stay-at-home" non-explorers.
In the new study, another gene variant also stood out as an important indicator of butterfly flight ability. New-population females were more often missing a small part of the succinate dehydrogenase gene (Sdhd) and this small deletion was associated with the ability to maintain flight for a greater duration. "The Pgi gene variant seems to be associated with sprinting, and the Sdhd gene variant appears to be associated with endurance," Marden said. "It's easy to see why these traits and their associated genes would be found at higher frequencies in new populations. Better flight ability allows certain butterflies to be able to reach and settle new habitat patches."
|Contact: Barbara Kennedy|