quote:
A species of fruit fly that started laying its eggs in old world apple tree when they were brought over despite no genetic propensity for the type of fruit, the difference in seasonal variance eventually lead to enough of a pre-zygotic barrier that the species diverged genetically as well as behaviorally.
It has actually been found that there was a preexisting latitudinal cline in the maggot fly that predisposed it to shift to the new host:
"The importance of speciation without the complete
geographical separation of diverging populations (sympatric
speciation) has become increasingly accepted.
One of the textbook examples of recent speciation in
sympatry is the apple maggot fly Rhagoletis pomonella,
in which genetically differentiated host races feed on
either hawthorn or apple. Three recent articles by Feder
and collaborators show that the history of these host
races is more complicated than was previously realized.
Genes that differentiate races of flies that feed on either
apple or hawthorn are located in chromosomal
rearrangements. This variation forms a latitudinal cline
that must have been established long before apples
were available as hosts. Furthermore, there is also new
evidence for the very recent evolution of a derived preference
for volatile chemicals that are typical of apple
fruits among apple-feeding flies. These results show
that adaptation to apple populations has involved both
the sorting of ancestral adaptive variation and the selection
of novel mutations."
Jiggins, C. D., & Bridle, J. M. (2004). Speciation in the apple maggot fly: A blend of vintages? Trends in ecology and Evolution 19: 111-114
http://homepages.ed.ac.uk/...lications/JigginsBridle2004.pdf
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