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ON THE SCENT OF STANDING VARIATION FOR SPECIATION: BEHAVIORAL EVIDENCE FOR NATIVE SYMPATRIC HOST RACES OF RHAGOLETIS POMONELLA (DIPTERA: TEPHRITIDAE) IN THE SOUTHERN UNITED STATES
Author(s) -
Powell Thomas H. Q.,
Cha Dong H.,
Linn Charles E.,
Feder Jeffrey L.
Publication year - 2012
Publication title -
evolution
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.84
H-Index - 199
eISSN - 1558-5646
pISSN - 0014-3820
DOI - 10.1111/j.1558-5646.2012.01625.x
Subject(s) - rhagoletis , tephritidae , sympatric speciation , biology , malus , host (biology) , crataegus , reproductive isolation , apple tree , zoology , botany , ecology , pest analysis , population , demography , sociology
Standing variation can be critical for speciation. Here, we investigate the origins of fruit odor discrimination for Rhagoletis pomonella underlying the fly's sympatric shift in the northeastern United States from downy hawthorn ( Crataegus mollis ) to apple ( Malus domestica ). Because R. pomonella mate on host fruit, preferences for natal fruit volatiles generate prezygotic isolation. Apples emit volatiles that appear to be missing from gas chromatography/electroantennographic detection profiles for flies infesting downy hawthorns, raising the question of how R. pomonella evolved a preference for apple. In the southern United States, R. pomonella attacks several native hawthorns. Behaviorally active volatile blends for R. pomonella infesting southern hawthorns contain the missing apple volatiles, potentially explaining why downy hawthorn flies could have evolved to be sensitive to a blend of apple volatiles. Flight tunnel assays imply that southern hawthorn populations were not the antecedent of a preassembled apple race, as southern flies were not attracted to the apple volatile blend. Instead, behavioral evidence was found for southern host races on native hawthorns, complementing the story of the historical sympatric shift to introduced apple in the North and illustrating how R. pomonella may evolve novel combinations of agonist and antagonist responses to volatiles to use new fruit resources.