Evolution Revolution: Two Species Become One, Study Says
for National Geographic News
|July 27, 2005|
A newfound insect shows that two species can combine to create a third
species, and that humans may be unknowingly encouraging evolution,
according to researchers.
Most new animal species are believed to arise when a single species splits into two. But new animals can also be created when two species come together to create a single new species, the researchers say.
This two-become-one evolutionary process, common among plants, has long been considered extremely rare and unimportant among animals. The new study, based on a fly species found in the northeastern United States, suggests otherwise.
The Lonicera fly evolved as a hybrid of two existing U.S. species, the blueberry maggot and the snowberry maggot, according to the study. The newfound species is named after the honeysuckle plant (scientific name: Lonicera), which the insect's life cycle revolves around.
Humans may have indirectly "caused" the new species by introducing an Asian honeysuckle species to North America.
The fly began as a hybrid. A hybrid is a type of animal that is created from the mating of two other species. Mules, for example, are donkey-horse hybrids, but they can't breed with each other. Hybrids that aren't sterile may have the opportunity to become a full-blown new species.
For this to happen, the hybrid requires a distinct niche where it can evolve separately from its two parent species. For the Lonicera fly, the alien honeysuckle plant provided that niche.
As a result, the fly provides the first evidence that two different animal species can interbreed and evolve into a new, distinct animal if their hybrid moves to a new habitat, the study suggests.
Conducted by researchers from Pennsylvania State University's entomology department, the study will be reported tomorrow in the journal Nature.
The team established the insect's hybrid origins through detailed DNA "fingerprinting" techniques.
Many other animals, particularly parasitic insects whose life cycles depend on a particular host plant, may also have arisen through hybridization, says the study's lead author, evolutionary ecologist Dietmar Schwarz. The difficulty, he says, is in detecting this method of evolution.
"The problem is detection, which requires extensive genetic studies," Schwarz said. "In animals there has been so far only limited information on this mode of speciation."
George Turner is a professor of evolutionary biology and biodiversity at the University of Hull in England. He agrees that animal evolution through hybridization may be much more widespread than previously believed.
As DNA analysis of different species becomes more sophisticated and extensive, he expects other examples to emerge.
"I think this kind of speciation is most likely in animals were there are lots of similar, fast-evolving species, such as in certain types of insects and fish," he added.
Turner says recent evidence indicates that some fish species also evolved as hybrids.
German researchers have studied cichlids (a type of tropical freshwater fish) living in tiny volcano-crater lakes in Cameroon, West Africa. Their studies have shown that at least one cichlid species started off as a hybrid.
Among cichlids this process likely takes thousands of years. The Lonicera fly's evolution, however, has occurred only in the 250 years since its honeysuckle host plant arrived in North America.
The introduction, via humans, of non-native species makes speciation through hybridization more likely, says Schwarz, the Penn State ecologist.
"On the one hand, introduced organisms provide new habitats," he said. "On the other, one could imagine that introducing a parasite that is closely related to a native species could lead to hybridization and, as a consequence, to the formation of new [species] that might be able to utilize a previously unused host."
"Evolution hasn't ended," George Turner added. "New species are evolving, and humans can have a big influence on that process."
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