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Site-specific genetic divergence in parallel hybrid zones suggests non-allopatric evolution of reproductive barriers

  • Marina Panova
  • Johan Hollander
  • Kerstin Johannesson
Publishing year: 2006
Language: English
Pages: 4021-4031
Publication/Series: Molecular Ecology
Volume: 15
Issue: 13
Document type: Journal article
Publisher: Wiley-Blackwell

Abstract english

The evolution of reproductive isolation in the presence of gene flow is supported by theoretical models but rarely by data. Empirical support might be gained from studies of parallel hybrid zones between interbreeding taxa. We analysed gene flow over two hybrid zones separating ecotypes of Littorina saxatilis to test the expectation that neutral genetic markers

will show site-specific differences if barriers have evolved in situ. Distinct ecotypes found in contrasting shore habitats are separated by divergent selection and poor dispersal, but hybrid zones appear between them. Swedish islands formed by postglacial uplift 5000 years ago provide opportunities to assess genetic structure in a recently evolved system. Each island houses a discrete population containing subpopulations of different ecotypes. Hybrid zones between ecotypes may be a product of ecological divergence occurring on each island or a consequence of secondary overlap of ecotypes of allopatric origin that have spread among the islands. We used six microsatellite loci to assess gene flow and

genetic profiles of hybrid zones on two islands. We found reduced gene flow over both hybrid zones, indicating the presence of local reproductive barriers between ecotypes. Nevertheless, subpopulations of different ecotypes from the same island were genetically more similar to each other than were subpopulations of the same ecotype from different islands. Moreover, neutral genetic traits separating the two ecotypes across hybrid zones were site-specific. This supports a scenario of in situ origin of ecotypes by ecological divergence and nonallopatric evolution of reproductive barriers.


  • Ecology
  • assortative mating
  • ecological speciation
  • Littorina saxatilis
  • microsatellites
  • morphometrics
  • parallel speciation


  • ISSN: 0962-1083
Johan Hollander
E-mail: johan [dot] hollander [at] biol [dot] lu [dot] se


Division aquatic ecology

+46 46 222 34 73


Sölvegatan 37, Lund



Aquatic Ecology