Scriber, J. M., G. Ording, and R. Mercader. 2008. Introgression and parapatric speciation in a hybrid zone. Pages 69-87 in K. Tilman, ed. Specialization, Speciation, and Radiation: The Evolutionary Biology of Herbivorous Insects. .

Hybridization has been recognized as a potent evolutionary force that rapidly can generate new (novel) gene combinations for adaptive evolution and speciation. However, others have historically viewed it as a minor evolutionary force (barring allopolyploids in plants), or simply as a local or transient type of evolutionary noise or dead end. While definitive proof is generally lacking, especially for animals, diploid hybrid recombinant speciation may represent a mechanism of evolution of new species, especially if it occurs rapidly. The rarity of animal hybrid speciation may be partly due to the difficulty in detection of hybrids (until the use of recent technological tools). This chapter explores introgression and parapatric speciation in a hybrid zone. First, it describes hybrid zones and “evolutionary novelties,” and then discusses isolation, climate warming, thermal constraints, voltinism, diapause, genetics of diapause regulation, and non-concordant steep clines for species-diagnostic allozymes. Finally, the chapter studies the tiger swallowtail butterflies, and the hybrid Papilio populations and species.

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