Speciation in Action: Fruit Fly Evolution Causes Cascading Changes In Wasp Species

Plants, animals and even humans are constantly evolving and adapting to changing situations, but scientists rarely catch a species in the act. A team of researchers recently had this unique opportunity and are staying tuned in as a fruit fly species, Rhagoletis pomonella – also known as the "apple maggot" – diverges into two new species. This evolution is expected to have a domino effect on three species of predatory wasps, a new study reveals. 

"Our study addresses one of the central questions in biology: How do new forms of life originate?" Scott Egan, an evolutionary biologist from Rice University and a co-author of the new study, said in a news release. "Our new work takes a close look at the evolutionary process termed 'sequential speciation. Sequential speciation identifies the fact that adaptation and speciation of one species is not an isolated process. The appearance of a new species creates new niche opportunities that can be exploited by other species, and that opportunity can promote the origin of other new species."

The apple maggot began plaguing U.S. apple growers in the 1850s and is native to North America. Originally, the inset fed on the fruit of a wild hawthorn. However, it later came to prefer feeding on cultivated apples that ripen in the summer or late fall.     

For their study, biologists from Rice University, the University of Notre Dame, Michigan State University, the University of Iowa and the University of Florida closely traced the evolutionary changes in the fruit flies' feeding and mating habits. Currently, Rhagoletis is in the act of evolving into two species as the result of differently timed fruiting cycles among apple trees. By examining the effects of this speciation beyond Rhagoletis, researchers found that three species of parasitic wasps are also affected by the change.

Researchers came to that conclusion after collecting wasps from different fruit fly host plant environments in the wild. In doing so, they found that all three wasp species were also undergoing speciation, or diverging into two new species. When this happens, a species' behavior, physiology and genetics are all altered. 

"The new study extends the earlier work by showing that new fruit fly species provide suitable habitat not just for one new parasitoid species, but for multiple new species," James Smith, co-author of the study and an entomologist from Michigan State, said in a statement.  

This domino effect may help researchers better understand why certain organisms, such as plants and insects, are more diverse than others. 

"Why are there so many insect species?" Smith asked. "Speciation cascades provide one explanation for how a lot of species might be generated in a relatively short period of time."

The findings were recently published in the Proceedings of the National Academy of Sciences.

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