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International Journal of Ecology
Volume 2011 (2011), Article ID 435357, 15 pages
Research Article

Ecological Divergence and the Origins of Intrinsic Postmating Isolation with Gene Flow

1Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, ON, Canada M5S 3B2
2Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556, USA
3Institute for Advanced Study, Wissenschaftskolleg, 14193 Berlin, Germany
4Department of Ecology and Evolutionary Biology, University of Boulder, Boulder, CO 80309, USA

Received 25 April 2011; Revised 14 June 2011; Accepted 21 June 2011

Academic Editor: Zachariah Gompert

Copyright © 2011 Aneil F. Agrawal et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The evolution of intrinsic postmating isolation has received much attention, both historically and in recent studies of speciation genes. Intrinsic isolation often stems from between-locus genetic incompatibilities, where alleles that function well within species are incompatible with one another when brought together in the genome of a hybrid. It can be difficult for such incompatibilities to originate when populations diverge with gene flow, because deleterious genotypic combinations will be created and then purged by selection. However, it has been argued that if genes underlying incompatibilities are themselves subject to divergent selection, then they might overcome gene flow to diverge between populations, resulting in the origin of incompatibilities. Nonetheless, there has been little explicit mathematical exploration of such scenarios for the origin of intrinsic incompatibilities during ecological speciation with gene flow. Here we explore theoretical models for the origin of intrinsic isolation where genes subject to divergent natural selection also affect intrinsic isolation, either directly or via linkage disequilibrium with other loci. Such genes indeed overcome gene flow, diverge between populations, and thus result in the evolution of intrinsic isolation. We also examine barriers to neutral gene flow. Surprisingly, we find that intrinsic isolation sometimes weakens this barrier, by impeding differentiation via ecologically based divergent selection.