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Reinforcement of stickleback mate preferences : sympatry breeds contempt

University of British Columbia

Detailed studies of reproductive isolation and how it varies among populations can provide valuable insight into fundamental questions concerning mechanisms of speciation. Here I investigate how the strength of prezygotic isolation varies between sympatric and allopatric populations of threespine sticklebacks to test a prediction of the hypothesis of reinforcement: that female mate preferences should be stronger in sympatry than allopatry. Ecological character displacement between sympatric species may cause significant divergence in phenotypes which might strengthen prezygotic isolation as a by-product of these changes. I control for ecological character displacement by comparing mate preferences of sympatric females (Benthics) with mate preferences of allopatric females that closely resemble the sympatric Benthic females in ecology and morphology. No-choice mating trials indicate that sympatric Benthic females mate less readily with heterospecific (Limnetic) than conspecific (Benthic) males, whereas two different populations of allopatric females resembling Benthics show no such discrimination. These differences demonstrate reproductive character displacement of mate preferences of Benthic females. Previous studies have established that hybridization between sympatric species has occurred in the past in the wild and that hybrid offspring have lower fitness than either parental species. This provides the conditions under which natural selection would favour individuals that do not hybridize. The results are therefore consistent with the hypothesis that female mate preferences have evolved as a response to selection against hybridization (reinforcement), although direct effects of sympatry or a biased extinction process could also produce the pattern. Males of the other sympatric species (Limnetics) showed a preference for smaller females, in contrast to the inferred ancestral preference for larger females. This suggests that reproductive character displacement of mate preferences has occurred in Limnetic males as well.

Thesis/Dissertation

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2009-03-24

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http://hdl.handle.net/2429/6366

Zoology

University of British Columbia

UBCV

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