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ECOLOGICAL SPECIATION IN STICKLEBACKS: ENVIRONMENT‐DEPENDENT HYBRID FITNESS
Author(s) -
Hatfield Todd,
Schluter Dolph
Publication year - 1999
Publication title -
evolution
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.84
H-Index - 199
eISSN - 1558-5646
pISSN - 0014-3820
DOI - 10.1111/j.1558-5646.1999.tb05380.x
Subject(s) - biology , hybrid , sympatric speciation , ecological speciation , reproductive isolation , hybrid zone , stickleback , limnetic zone , genetic algorithm , ecology , gasterosteus , habitat , sympatry , ecological selection , incipient speciation , disruptive selection , selection (genetic algorithm) , littoral zone , allopatric speciation , natural selection , genetic variation , population , gene flow , fishery , biochemistry , botany , demography , artificial intelligence , sociology , gene , fish <actinopterygii> , computer science
“Ecological” speciation occurs when reproductive isolation evolves as a consequence of divergent selection between populations exploiting different resources or environments. We tested this hypothesis of speciation in a young stickleback species pair by measuring the direct contribution of ecological selection pressures to hybrid fitness. The two species (limnetic and benthic) are strongly differentiated morphologically and ecologically, whereas hybrids are intermediate. Fitness of hybrids is high in the laboratory, especially F 1 and F 2 hybrids (backcrosses may show some breakdown). We transplanted F 1 hybrids to enclosures in the two main habitats in the wild to test whether the distribution of resources available in the environment generates a hybrid disadvantage not detectable in the laboratory. Hybrids grew more slowly than limnetics in the open water habitat and more slowly than benthics in the littoral zone. Growth of F 1 hybrids was inferior to the average of the parent species across both habitats, albeit not significantly. The contrast between laboratory and field results supports the hypothesis that mechanisms of F 1 hybrid fitness in the wild are primarily ecological and do not result from intrinsic genetic incompatibilities. Direct selection on hybrids contributes to the maintenance of sympatric stickleback species and may have played an important role in their origin.