title: The genetic structure of hawthorn-infesting Rhagoletis pomonella populations in Mexico: implications for sympatric host race formation.
abstract: The genetic origins of species may not all trace to the same time and place as the proximate cause(s) for population divergence. Moreover, inherent gene-flow barriers separating populations may not all have evolved under the same geographical circumstances. These considerations have lead to a greater appreciation of the plurality of speciation: that one geographical mode for divergence may not always be sufficient to describe a speciation event. The apple maggot fly, Rhagoletis pomonella, a model system for sympatric speciation via host-plant shifting, has been a surprising contributor to the concept of speciation mode plurality. Previous studies have suggested that past introgression of inversion polymorphism from a hawthorn-fly population in the trans-Mexican volcanic belt (EVTM) introduced diapause life-history variation into a more northern fly population that subsequently contributed to sympatric host race formation and speciation in the United States (US). Here, we report results from a microsatellite survey implying (i) that volcanic activity in the eastern EVTM may have been responsible for the initial geographical isolation of the Mexican and northern hawthorn-fly populations c. 1.57 mya; and (ii) that flies in the Sierra Madre Oriental Mountains (SMO) likely served as a conduit for past gene flow from the EVTM into the US. Indeed, the microsatellite data suggest that the current US population may represent a range expansion from the northern SMO. We discuss the implications of these findings for sympatric race formation in Rhagoletis and speciation theory.
authors.affiliation: Department of Biological Sciences, PO Box 369, Galvin Life Sciences Building, University of Notre Dame, Notre Dame, IN 46556-0369, USA.
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Michel
authors.forename: Juan
authors.initials: J
authors.lastname: Rull
authors.forename: Martin
authors.initials: M
authors.lastname: Aluja
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Feder
mesh_terms: D000483:Alleles; D000818:Animals; D027825:Crataegus / Q000469:parasitology*; D049810:Genetic Speciation; D014644:Genetic Variation; D005843:Geography; D008800:Mexico; D018895:Microsatellite Repeats / Q000235:genetics; D011157:Population Dynamics; D033621:Tephritidae / Q000235:genetics*; D014481:United States