The fruit flies in question evolved into new species when they began laying their eggs and mating on apple trees, as opposed to their native hawthorn tree hosts. Three different kinds of parasitoid wasps were collected from a number of different fly host plant environments in the wild.
Analyses in the lab showed that all three of the different kinds of wasps had diverged from others of the same kind, both genetically and with respect to host-associated physiology and behavior.
“In a sense,” Smith said, “they have caught an entire community of parasitoids actively ecologically diverging in response to a historically documented host plant shift of their fly host.”
These evolutionary changes, known as “sequential” or “cascading” events, may provide additional information helping explain why some groups of organisms, such as plants, the insects that feed on them and the parasites that attack the insects, are more diverse and species-rich than other groups. More.
Okay, but how are we defining speciation here? I keep hearing different definitions. In the abstract below, we are—seemingly—to accept “(host-associated differences in the timing of adult eclosion, host fruit odor preference and avoidance behaviors, and mating site fidelity).” But how sure or final are these criteria?
Couldn’t these factors all change with a shift in the ecology, as happened with Darwin’s finches, or be constantly subject to boundary movements, like the saga of wolves and dogs?
If it were not for the chance to defend Darwinism by the proclamation of “new species,” wouldn’t there be more general dissatisfaction with such a slippery scale? Readers?
See also: What’s happened since Icons of Evolution (2002)?
The Economist discovers a “new species”
Here’s the abstract:
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. (paywall) – Glen R. Hood, Andrew A. Forbes, Thomas H. Q. Powell, Scott P. Egan, Gabriela Hamerlinck, James J. Smith, Jeffrey L. Feder. Sequential divergence and the multiplicative origin of community diversity. Proceedings of the National Academy of Sciences, 2015; 201424717 DOI: 10.1073/pnas.1424717112
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