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Evolutionary Ecology Research, 2010, 12: 523–544 Recombination and epistasis facilitate introgressive hybridization across reproductively isolated populations: a gamete-based simulation Yoshinari Tanaka Center for Environmental Risk, National Institute for Environmental Studies, Tsukuba, Japan ABSTRACT Questions: Why can invasive species sometimes genetically contaminate closely related indigenous species by introgressive hybridization, resisting the post-zygotic isolating mechanism? How do recombination rates and epistasis among incompatibility genes, and the number of loci affect the introgression? Features of models: The individual-based model and gamete-based model, which tracks changes in the number of invasive genes per gamete due to selection and recombination by assuming random arrangement of genes within gamete. Range of key variables: The recombination rate between adjacent loci ranges from 0 to 0.4. The epistatic effect between loci is measured by the exponent of the geometric function of heterozygosities representing individual fitness. It ranges from 1 (additive) to 4 (strong epistasis). The number of loci is set to 2–10 for the gamete-based model. Conclusions: Provided that the number of loci is not very small and the fitness of the F1 hybrid is not extremely low, complete genetic replacement by introgressive hybridization is accelerated by an increase in rates of total recombination across all loci and by the epistatic fitness effect among incompatibility loci. Keywords: Dobzhansky-Mueller model, epistasis, gamete-based model, introgressive hybridization, multi-locus underdominance, post-zygotic isolation. INTRODUCTION Introgressive hybridization by anthropogenic transference of exotic species brings about genetic contamination of endemic species, which, in some extreme cases, leads to genetic extinction of the endemic population by complete genetic assimilation or replacement by the invasive population (Levin et al., 1995; Rieseberg and Gerber, 1995; Rhymer and Simberloff, 1996; Epifanio and Nielsen, 2000; Mallet, 2005). Apart from ecological factors such as predation and competition by biotic invasion, hybridization of endemic species with closely related invading species or subspecies poses Correspondence: Y. Tanaka, Center for Environmental Risk, National Institute for Environmental Studies, Onogawa 16-2, Tsukuba, Ibaraki 305-8506, Japan. e-mail: [email protected] Consult the copyright statement on the inside front cover for non-commercial copying policies. © 2010 Yoshinari Tanaka www.evolutionary-ecology.com Evolutionary Ecology Research is delighted that you wish to consult one of its articles. You may if your library or laboratory subscribes. Ask your librarian or library committee why your place does not already subscribe to the low-cost journal that is publishing splendid science in a socially responsible manner. EER's low prices have helped librarians to rein in the indefensible cost increases that have reduced our access to science all over the world! Just ask our partners at SPARC — the Scholarly Publishing & Academic Resources Coalition of the Association of Research Libraries. Or maybe you should just remind the folks who order your journals to contact us and subscribe! You need — and they should support — the journal that: Invented the instant publication of reviewed, revised and accepted e-editions. Vests the copyrights of all articles in their authors while preserving the rights of educational and research groups to use its material in classes, seminars, etc. at no additional cost. Maintains a unified data-base of articles, thus doing away with your need to worry about issue numbers, author order, and other such impediments to easy access. Provides Webglimpse so that you can search any word, place, species, variable, phrase or author in any article EER has ever published. Pioneered e-only subscriptions while maintaining, at the same time, a traditional print edition, too. Some 10,000 readers per week have it right. EER is the place to go for great science, responsible publication policies and easy access! Click here for the Table of Contents of the most recent issue of Evolutionary Ecology Research Click here for full access to a sample issue of Evolutionary Ecology Research Click here for SUBSCRIPTION INFORMATION