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Proc Biol Sci. 2000 August 22; 267(1453): 1649–1655.
PMCID: PMC1690725

Reinforcement and divergence under assortative mating.


Traits that cause assortative mating such as the flowering time in plants and body size in animals can produce reproductive isolation between hybridizing populations. Can selection against unfit hybrids cause two populations to diverge in their mean values for these kinds of traits? Here I present a haploid analytical model of one population that receives gene flow from another. The partial pre-zygotic isolation between the two populations is caused by assortative mating for a trait that is influenced by any number of genes with additive effects. The post-zygotic isolation is caused by selection against genetic incompatibilities that can involve any form of selection on individual genes and gene combinations (epistasis). The analysis assumes that the introgression rate and selection coefficients are small. The results show that the assortment trait mean will not diverge from the immigrants unless there is direct selection on the trait favouring it to do so or there are genes of very large effect. The amount of divergence at equilibrium is determined by a balance between direct selection on the assortment trait and introgression from the other population. Additional selection against hybrid genetic incompatibilities reduces the effective migration rate and allows greater divergence. The role of assortment in speciation is discussed in the light of these results.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.
  • Barton NH, Turelli M. Natural and sexual selection on many loci. Genetics. 1991 Jan;127(1):229–255. [PubMed]
  • Karlin S, Scudo FM. Assortative mating based on phenotype. II. Two autosomal alleles without dominance. Genetics. 1969 Oct;63(2):499–510. [PubMed]
  • Kelly JK, Noor MA. Speciation by reinforcement: a model derived from studies of Drosophila. Genetics. 1996 Jul;143(3):1485–1497. [PubMed]
  • Kimura M. Attainment of Quasi Linkage Equilibrium When Gene Frequencies Are Changing by Natural Selection. Genetics. 1965 Nov;52(5):875–890. [PubMed]
  • Kirkpatrick M, Barton NH. The strength of indirect selection on female mating preferences. Proc Natl Acad Sci U S A. 1997 Feb 18;94(4):1282–1286. [PubMed]
  • Lewontin R, Kirk D, Crow J. Selective mating, assortative mating, and inbreeding: definitions and implications. Eugen Q. 1968 Jun;15(2):141–143. [PubMed]
  • Nagylaki T. The evolution of one- and two-locus systems. Genetics. 1976 Jul;83(3 PT2):583–600. [PubMed]
  • Orr HA. The population genetics of speciation: the evolution of hybrid incompatibilities. Genetics. 1995 Apr;139(4):1805–1813. [PubMed]
  • Rundle HD, Nagel L, Wenrick Boughman J, Schluter D. Natural selection and parallel speciation in sympatric sticklebacks. Science. 2000 Jan 14;287(5451):306–308. [PubMed]
  • Schemske DW, Bradshaw HD., Jr Pollinator preference and the evolution of floral traits in monkeyflowers (Mimulus). Proc Natl Acad Sci U S A. 1999 Oct 12;96(21):11910–11915. [PubMed]
  • Scudo FM, Karlin S. Assortative mating based on phenotype. I. Two alleles with dominance. Genetics. 1969 Oct;63(2):479–498. [PubMed]
  • Servedio MR. Reinforcement and the genetics of nonrandom mating. Evolution. 2000 Feb;54(1):21–29. [PubMed]
  • Wright S. Systems of Mating. III. Assortative Mating Based on Somatic Resemblance. Genetics. 1921 Mar;6(2):144–161. [PubMed]

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