Biodiversity caused by … biodiversity?

UC Davis evolutionary ecologist Andrew Forbes may have made a discovery that will add another chapter to high school biology books everywhere.

Published in Science, his findings suggest that a major cause for biodiversity in the ecosystem may be diversity itself. While Darwin had his finches, Forbes has his flies, the apple maggots.

Apple maggots, Rhagoletis pomonella, are flies that lay their eggs in ripe fruit, causing the fruit to go bad. They are known to be a major pest in the apple industry. Before apples were introduced in Europe around 250 years ago, apple maggots infested the native hawthorn trees, according to the UC Davis ecology department‘s website.

Forbes‘ research shows that when the apple maggots shifted from hawthorns to apples, it created a cascading effect, eventually affecting a predator of the apple maggot – a parasitic wasp – to the point of speciation, the evolution of a new species.

The parasitic wasp, Diachasma alloeum, lays its own eggs into the larva of the apple maggots as it eats the apple. The infant wasp feeds on its new host and in a year‘s time, emerges from its pupa as a new wasp.

“We have enough evidence to show that the apple maggots and their ancestral populations have developed temporal, behavioral and genetic differences,“ Forbes said in an e-mail interview. “Now that this new ‘race‘ of fly exists, it represents a new ecological and evolutionary opportunity for other organisms to exploit and our research shows that a parasitoid wasp has exploited the apple race of flies and is also in the process of forming a new species.“

Determining when a population has become a new species is not a clear-cut consensus among biologists, Forbes said. However, many researchers, including UC Davis professor of entomology and director of the center for biosystematics Lynn Kimsey, consider the inability to reproduce as a defining characteristic of speciation.

“[Most researchers] use the inability to reproduce, a sort of reproductive isolation,“ Kimsey said.

However, apple maggots and parasitic wasps, fail in this test. They are still sexually compatible to their ancestral counterparts, and are therefore considered host races. They can still produce offspring, Forbes said, but it is unclear whether the offspring are viable and fertile.

“The genetic changes [in both the wasps and flies] are starting to accumulate and so eventually [we believe] that they will become completely incompatible,“ Kimsey said. “Speciation in insects takes a very long time.“

Not only does this research suggest the likeliness that biodiversity begets biodiversity, but it shows the “tangled bank of life“ as Forbes describes.

“[The tangled bank of life] refers to the interconnectedness of organisms and how they interact with other organisms in a delicate balance,“ Forbes said. “If this balance is altered, that‘s when change happens.“

NICK MARKWITH can be reached at campus@theaggie.org.