Speciation in the apple maggot fly: a blend of vintages?

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.