Near Darwin's bicentennial, UF researchers help reveal hidden aspect of evolutionary theory
February 5, 2009
GAINESVILLE, Fla. — Although widely speculated, researchers have now shown that the evolution of one species can drive the evolution of another.
For the first time, researchers from the University of Florida, the University of Notre Dame and Michigan State University have documented what evolutionary biologists call “cascading speciation.” In the Feb. 6 issue of the journal Science, they describe how the continuing evolution of a fly species directly triggers changes in a wasp that preys on those flies — a powerful demonstration of the complexity of Darwin’s theory.
“This is the sort of thing that scientists know is happening, but is almost impossible to show in nature because it happens over large areas over long periods of time,” said Lukasz Stelinski, an entomologist with UF’s Institute of Food and Agricultural Sciences. “In this instance, it happened very quickly and virtually in our own backyard.”
Of course, “quickly” is a relative term to biologists.
Charles Darwin and John Chapman (a.k.a. Johnny Appleseed) probably never met. The year Darwin was born, 1809, Appleseed was in the midst of spreading orchards across America’s frontier lands. Nevertheless, as Darwin’s bicentennial approaches, it turns out that Appleseed helped lay the foundation for this modern evolution research.
As apple trees were spread, some members of a fly species that had previously been laying its eggs in the berry-like fruit of the hawthorn plant began instead infesting the newly available apples.
Because the new fruit ripened at a different time of the year, emitted different fragrances and had an entirely different texture for the larvae to burrow through, these deviant flies, now commonly called apple maggots, began to change to best accommodate their new breeding ground.
However, the flies weren’t alone in this change. A wasp that used the fly larvae as a host for its eggs followed the flies along their evolutionary journey — changing to adapt to the new timing, fragrance and physical qualities of the fruit.
The flies and wasps haven’t completely changed species yet, although the apple flies and wasps have very different lives than their hawthorn kin. The definition of a new species is an animal that can no longer mate with its predecessor and produce fertile offspring, and the researchers do observe that a small amount of mating still occurs.
The researchers were able to document the ongoing change by collecting thousands of samples of the flies and wasps across Illinois, Michigan, Pennsylvania and New Jersey. Through behavioral, genetic and physiological analyses, they were able to chart gradual differences that are marking one species’ journey to the next.
“This was probably one of the simplest, clearest examples that we could have studied,” said Andrew Forbes, an entomologist at the University of Notre Dame at the time of the research and now with the University of California, Davis. “And, yeah, it was still a pretty massive undertaking. But, hopefully, this will open the door and encourage others to study this aspect of nature — and draw some attention to the really marvelous diversity of insects.”