What is an example of sympatric speciation?

An example of sympatric speciation can be seen in the change in the egg-laying habits of the apple maggot, first observed in the early 19th century. The sympatric speciation of the apple maggot fly occurred as a result of changes in the plants on which the females laid their eggs.

Sympatric speciation describes speciation that occurs in the absence of geographic isolation, when some members of a species reproduce a mutation despite the abundance of the non-mutated gene in the gene pool. For example, when apple maggots began laying eggs on domestic apple leaves rather than hawthorne leaves, the species began to undergo sympatric speciation. Sympatric speciation is a relatively rare form of speciation.