A recently criticized textbook example of evolutionary forces in action, the dark forms of peppered moths that spread with industrialization in Britain, may be on its way back.
Results of an ambitious experiment on the moths (Biston betularia) support the original hypothesis that their dark-colored forms spread in soot-coated landscapes because they are more difficult for hungry birds to spot, says evolutionary biologist James Mallet of Harvard University. He and three colleagues have published the final peppered moth experiment of Michael Majerus, who spent six years monitoring the fates of a total of 4,864 moths, presented his conclusions at a conference but died before publishing them. The study appears online February 8 in Biology Letters.
The moth story not only makes “a compelling example of evolution in action,” but it's “a terrific case history of how science works,” says evolutionary biologist Scott Freeman of the University of Washington in Seattle. “Majerus raised questions; he and his colleagues did the hard work required to answer them.”
The moths, which usually have salt-white wings sprinkled with pepper-black, have long played a role in evolutionary biology. In the early years of genetics, breeding experiments established that a single gene can create a black form. It showed up in Manchester, England, in 1848, and by 1895, 98 percent of the region's moths were dark. Moths went dark in similarly industrializing areas, and when clean-air regulations began to clear the pollution, dark forms went into decline.
Experiments in the mid-20th century supported the idea that industrial grime provided better camouflage for dark wings, but that work drew escalating challenges starting in the 1990s. Majerus and other scientists raised questions about those studies' methods, such as whether the high densities of moths released had altered the results and whether the tree trunks where moths were placed were a normal resting place.
No comments:
Post a Comment