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.
Recent research by a team of US scientists finds that evolutionary changes, in this case in a new species of fruit fly, have an almost domino effect on a number of species. The apple maggot flies 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. 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.
The new study extends the earlier work by showing that new fruit fly species provide suitable habitat not just for one new parasitoid species, but for multiple new species. In a sense they have caught an entire community of parasitoids actively ecologically diverging in response to a historically documented host plant shift of their fly host.