We often think of evolution as something which occurs slowly over millions of years, only being recorded in the fossils that are left behind. But evolution is gradual, with species constantly changing in response to a host of different pressures, from alterations in their environment to changes in other species they reply on. This last point, of species evolving and splitting in response to other species evolving and splitting, is a central concept in biodiversity, but is also a difficult one to prove.
A new study has, however, apparently done just this. Researchers from Rice University have documented how as one species of fruit fly is evolving into two separate species that exploit different food, three species of wasp, which parasitize the fruit fly, are also splitting into six new species. This proves how as habitats become more complex, with increasing numbers of species present, it forms a feedback loop that in turn causes yet more species to evolve.
The friut fly Rhagoletis pomonella is diverging into two seperate species, one which lives on apples and another on hawthorn fruit. Andrew Forbes.
“Our study addresses one of the central questions in biology: How do new forms of life originate?” Scott Egan, who co-authored the paper published in the Proceedings of the National Academy of Sciences, said in a statement. “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 original species of fruit fly in question, Rhagoletis pomonella, is native to the U.S. and normally lays its eggs on the fruit of the North American hawthorn. But around the 1850s some of the flies instead started to lay their eggs on apples. Due to the differences in fruiting cycles between apples and hawthorn, and the fact that some flies preferred one over the other, populations of fruit flies within the same area became sexually separated, thus leading to divergences and the beginning of two separate species.
Knowing this, the researchers focused on three species of wasp that parasitize the flies by infecting the larvae. Here they found that each individual wasp species was also diverging into two separate species, not just in the way they behaved, but also genetically and in how they were physically adapted to exploit their hosts. These findings, and that the speciation seems to undergo ‘sequential’ events, could help evolutionary biologists understand why insects as a group are so diverse when compared to other groups such as mammals.