Journal
EVOLUTION
Volume 66, Issue 2, Pages 419-434Publisher
WILEY
DOI: 10.1111/j.1558-5646.2011.01441.x
Keywords
Craniofacial; G matrix; Gasterosteus aculeatus; genetic basis of traits; genetic bias; genetic constraint; microevolution; quantitative genetics
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Funding
- US National Science Foundation [IOS-0618738, IOS-0642264]
- University of Oregon
- University of Queensland
- Australian Research Council
- Direct For Biological Sciences
- Division Of Environmental Biology [0919090, 0919234] Funding Source: National Science Foundation
- Direct For Biological Sciences
- Division Of Integrative Organismal Systems [0818738] Funding Source: National Science Foundation
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Evolution of similar phenotypes in independent populations is often taken as evidence of adaptation to the same fitness optimum. However, the genetic architecture of traits might cause evolution to proceed more often toward particular phenotypes, and less often toward others, independently of the adaptive value of the traits. Freshwater populations of Alaskan threespine stickleback have repeatedly evolved the same distinctive opercle shape after divergence from an oceanic ancestor. Here we demonstrate that this pattern of parallel evolution is widespread, distinguishing oceanic and freshwater populations across the Pacific Coast of North America and Iceland. We test whether this parallel evolution reflects genetic bias by estimating the additive genetic variancecovariance matrix (G) of opercle shape in an Alaskan oceanic (putative ancestral) population. We find significant additive genetic variance for opercle shape and that G has the potential to be biasing, because of the existence of regions of phenotypic space with low additive genetic variation. However, evolution did not occur along major eigenvectors of G, rather it occurred repeatedly in the same directions of high evolvability. We conclude that the parallel opercle evolution is most likely due to selection during adaptation to freshwater habitats, rather than due to biasing effects of opercle genetic architecture.
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