It’s the evolutionary version of the domino effect: ongoing changes in one species of fruit fly have played a key role in the rise of three new types of predatory wasps, according to research published earlier this week by the Proceedings of the National Academy of Sciences.
In the new study, biologists from Rice University, the University of Notre Dame, Michigan State University, the University of Iowa, and the University of Florida explained that they were looking at the “apple maggot,” a fruit fly species known as Rhagoletis pomonella, that previous work had found was becoming two different species due to feeding and mating habit changes.
That evolutionary split is driven by differently timed fruiting cycles between apple trees, which the study authors explained are preferred by some Rhagoletis, and the North American hawthorn, where the fruit flies had traditionally laid their eggs. The new study expands on that earlier work to investigate the impact of those changes on wasps known to be parasites for Rhagoletis.
Specimens from three different species of wasp were collected from various different fruit fly host plants in the wild. Analysis of those wasps revealed that just like Rhagoletis, they were in the process of diverging into different species, distinct both in terms of their genes and in terms of host-associated physiology and behavior.
One good evolutionary adaptation deserves another
Study co-author Scott Egan, an evolutionary biologist and assistant professor of biosciences at Rice, explained in a statement that the study “addresses one of the central questions in biology: How do new forms of life originate?” He added that it examines “sequential speciation,” a type of evolutionary process that recognizes that adaptation is not an isolated process.
When a new species appears, as is the case with the apple maggots, it can create a new niche opportunity that other species exploit, Egan added. That opportunity ultimately can lead to the evolution of an additional new species, as is happening with each of the three wasp species. The new fruit flies prove to be suitable targets for new kinds of parasites, the authors said.
These types of evolutionary changes, in which differentiation in one type of creature presents a new opportunity for adaptation in other species, are known as sequential or cascading events, and they help biologists explain why organisms such as insects tend to be more biodiverse than other groups of organisms. Such changes lead to the subsequent origin of new creatures, they noted.
In the case of the wasps and the fruit flies, Egan and his colleagues explained in their study that as the apple maggots “shift and adapt to new host plants, wasps follow suit and diverge in kind,” ultimately resulting in “a multiplicative increase of diversity as the effects of ecologically based divergent selection cascade through the ecosystem.”
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