Male Parasitic Wasp (Diachasma alloeum)

A male parasitic wasp (Diachasma alloeum) on an apple. This wasp is speciating in sympatry along with its host, the apple maggot (Rhagoletis pomonella).

Research by ecologist Andrew Forbes of the University of California, Davis, found that when the apple maggot shifted hosts from the hawthorn tree to the apple, it triggered a cascading effect on the ecosystem.

Forbes and his colleagues found that the wasp, which attacks the apple maggot, has formed new incipient species as a result of specializing on diversifying fly hosts, including the apple-infesting race of R. pomonella.

The apple maggot, which is native to North America, shifted from its ancestral hawthorn host (Crataegus spp.) to the introduced European apple less than 250 years ago. "The two populations," Forbes said, "have since become partially reproductively isolated due to a number of host-related adaptations and are now distinct host races" (a group of organisms in the process of becoming a new species due to their close association with a particular host plant or animal). Forbes says this example of speciation in action may tell us more about why certain groups of organisms are more diverse than others, as well as suggest why certain areas and/or biotic regions may have more species than others.

[Research supported by a dissertation grant from the National Science Foundation (DEB 07-09647).] [This picture is associated with the following study: Forbes, A.A., L.L. Stelinski, T.H.Q. Powell, J.J. Smith and J.L. Feder. 2009. Sequential sympatric speciation across trophic levels. Science. 323: 776-779.]

(Date of Image: 2006)

Credit: Andrew A. Forbes