Monday, 2 November 2015

Evolution In Progress: New Wasp Species Emerging

Utetes canaliculatus, one of the wasps in the process of evolving.
Sequential divergence and the multiplicative origin of community diversity | PNAS

And another mainstay of creationism - the nonsensical dogma that new species can't arise by evolution - comes crashing down, as does the dogma that speciation has never been observed.

Evolution is primarily driven by environmental change because these changes open up new opportunities for random variations to be an advantage in, so creating something for natural selection to select for (or not to select against). In this way, biodiversity feeds upon itself to give more biodiversity.

A lovely example of this in progress has just been published in the Proceedings of the National Academy of Sciences by biologists from Rice University, the University of Notre Dame, Michigan State University, the University of Iowa and the University of Florida. It builds on an earlier study showing that the native American fruit fly (Rhagoletis pomonella) is diverging into two species. The new form switched from living on hawthorn to living on cultivated apples about 160 years ago and by 1850 the 'apple maggot' had become a major pest on apple crops. This speciation is being driven by a change in feeding and mating habits which act as barriers to hybridization and reinforce gene pool isolation.

Now the researchers have shown how the emergence of two these two species where there was formerly just one, has created the conditions for three species of parasitoid wasp which parasitise these fruit flies to begin to speciate, each into two new species corresponding to the two new species of fruit fly.

Understanding how new life forms originate is a central question in biology. Population divergence is usually studied with respect to how single lineages diverge into daughter taxa. However, populations may not always differentiate in isolation; divergence of one taxon could create new niche opportunities in higher trophic levels, leading to the sequential origin of many new taxa. Here, we show that this may be occurring for three species of parasitoid wasps attacking Rhagoletis fruit flies. As flies shift and adapt to new host plants, wasps follow suit and diverge in kind, resulting in a multiplicative increase of diversity as the effects of ecologically based divergent selection cascade through the ecosystem. Biodiversity therefore may potentially beget increasing levels of biodiversity.

Phenotypic and genetic variation in one species can influence the composition of interacting organisms within communities and across ecosystems. As a result, the divergence of one species may not be an isolated process, as the origin of one taxon could create new niche opportunities for other species to exploit, leading to the genesis of many new taxa in a process termed “sequential divergence.” Here, we test for such a multiplicative effect of sequential divergence in a community of host-specific parasitoid wasps, Diachasma alloeum, Utetes canaliculatus, and Diachasmimorpha mellea (Hymenoptera: Braconidae), that attack Rhagoletis pomonella fruit flies (Diptera: Tephritidae). Flies in the R. pomonella species complex radiated by sympatrically shifting and ecologically adapting to new host plants, the most recent example being the apple-infesting host race of R. pomonella formed via a host plant shift from hawthorn-infesting flies within the last 160 y. Using population genetics, field-based behavioral observations, host fruit odor discrimination assays, and analyses of life history timing, we show that the same host-related ecological selection pressures that differentially adapt and reproductively isolate Rhagoletis to their respective host plants (host-associated differences in the timing of adult eclosion, host fruit odor preference and avoidance behaviors, and mating site fidelity) cascade through the ecosystem and induce host-associated genetic divergence for each of the three members of the parasitoid community. Thus, divergent selection at lower trophic levels can potentially multiplicatively and rapidly amplify biodiversity at higher levels on an ecological time scale, which may sequentially contribute to the rich diversity of life.*

Glen R. Hood, Andrew A. Forbes, Thomas H. Q. Powell, Scott P. Egan, Gabriela Hamerlinck, James J. Smith, and Jeffrey L. Feder
Sequential divergence and the multiplicative origin of community diversity
PNAS 2015 : 1424717112v1-201424717. doi: 10.1073/pnas.1424717112

*Copyright © National Academy of Sciences

Rhagoletis pomonella
So here we have a clear example of recent speciation in fruit flies, within the last 160 years, leading to the process of speciation now being detectable as three parasitoid wasps diverge into six species. And all this came about because of the introduction of commercial varieties of cultivated apples by humans. And of course, it's all perfectly explained by simple Darwinian evolution by natural selection acting on variation to select for those best fitted to survive and reproduce in newly-created ecological niches.

This study also shows how biodiversity itself evolves and how change doesn't occur in isolation but has a knock-on effect throughout the entire ecosystem.

As one of the authors, Scott Egan, explained:

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.

Time for creationists to redefine the term 'species' I guess, so that what used to be 'impossible' is possible, but the species goalpost is now over the other side of the field.

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