Bluejay writes:
...many species of fly and non-stinging wasp lay their eggs inside a host plant, and the larvae develop inside the host (these insects are called "parasitoids"). Some of these parasitoids may use multiple different host species. But, each plant will exert different selection pressures on the insect, so it's possible that those laying eggs in different plants will start to diverge.
What's worse than finding a worm in an apple? So everyone knows that apples sometimes have worms, actually the larvae of the apple maggot fly. The case is interesting because apples are not native to North America. They were cultivated from seeds brought from Europe. Thus, apple parasitoids didn't exist in North America. John Chapman (Johnny Appleseed) brought apple seeds from his native Massachusetts (where they had been cultivated from seeds brought from Europe) and planted apples in the Ohio River valley. He did that in the 1st half of the 19th century. He died in 1845. Shortly after that, in the 1850s, worms began to appear in apples. There are a couple of possibilities - special creation by a magical spirit, or the infestation of apples by a native species. The latter seems to be the case since the apple maggot fly is identical to the hawthorn maggot fly. There are several species of hawthorn in at least two genera that I know of in the family Rosaceae and the sub-family Maloideae that are all infested with the hawthorn maggot fly. The hawthorns, as well as the fly, are native to North America. As it happens, the apple is also in the Rosaceae family and the Maloideae sub-family. The problem for maggot flies is that they do not set fruit at the same time. They are separated by a period of weeks. But somehow, some poor female maggot fly was early/late (I'm not sure which) by enough time that the usual host species (the hawthorn) was not available, so it settled on an apple tree.
Studies have indicated that hawthorn maggot flies and apple maggot flies rarely, if ever, interbreed. Their reproduction is in sync with the time the various plants set fruit. Thus, they reach sexual maturity some weeks apart. Moreover, they just seem to prefer the host on which they were born.
There is also the pear maggot fly. Pears, like apples, are not native to North America, but they are in the same family and sub-family. Thus, they have also been infested by maggot flies. These various flies, even though they may inhabit the same territory, rarely interbreed. They prefer their particular host when there is a choice (established by experimentation) and their time of sexual maturity is in cycle with that host.
If these various parasitoids are not separate species, they are at the least obvious examples of incipient species. They are evidence of the fact that evolution happens, and in fact, that macroevolution happens or is in the process of happening.
The term for this, by the way, is sympatric specieation, i.e., the divergence of a single species into two (or more) species as events contingent on environmental opportunities.
But they are still maggot flies and but a single pair was aboard the ark with Noah.
Edited by pandion, : No reason given.
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