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International Journal of Ecology
Volume 2012 (2012), Article ID 902438, 14 pages
Research Article

Divergent Selection and Then What Not: The Conundrum of Missing Reproductive Isolation in Misty Lake and Stream Stickleback

1Redpath Museum and Department of Biology, McGill University, 859 Sherbrooke Street. W, Montreal, QC, Canada H3A 2K6
2Department of Aquatic Ecology, Eawag and ETH-Zurich, Institute of Integrative Biology, Ueberlandstraβe 133, 8600 Duebendorf, Switzerland
3Department of Biology and Centre for Advanced Research in Environmental Genomics, University of Ottawa, Ottawa, ON, Canada K1N 6N5

Received 1 July 2011; Accepted 28 October 2011

Academic Editor: Rui Faria

Copyright © 2012 Katja Räsänen 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.


In ecological speciation, reproductive isolation evolves as a consequence of adaptation to different selective environments. A frequent contributor to this process is the evolution of positive assortative mate choice between ecotypes. We tested this expectation for lake and inlet stream threespine stickleback (Gasterosteus aculeatus) from the Misty system (Vancouver Island, Canada), which show strong genetically based adaptive divergence and little genetic exchange in nature. This, and work on other stickleback systems, led us to expect positive assortative mating. Yet, our standard “no-choice” laboratory experiment on common-garden fish revealed no evidence for this—despite divergence in traits typically mediating assortative mating in stickleback. These results remind us that divergent natural selection may not inevitably lead to the evolution of positive assortative mate choice. The apparent lack of strong and symmetric reproductive barriers in this system presents a conundrum: why are such barriers not evident despite strong adaptive divergence and low gene flow in nature?