Hybridization between the blue mussels Mytilus galloprovincialis and M. trossulus along the Pacific coast of North America: evidence for limited introgression |
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Authors: | P D Rawson V Agrawal T J Hilbish |
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Institution: | (1) Department of Biological Sciences, University of South Carolina, Columbia, South Carolina 29208, USA, US |
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Abstract: | Two species of blue mussel, Mytilus galloprovincialis and M. trossulus, co-occur and hybridize along the Pacific coast of North America. Using a set of polymerase chain-reaction (PCR)-based genetic
markers which diagnostically identify these species, we show that they are sympatric from the Cape Mendocino region to the
Monterey Peninsula in northern and central California, USA. Mussels with hybrid genotypes were detected in all populations
sampled in the region of sympatry, and the frequency of hybrid genotypes in individual hybrid populations ranged from 13 to
44%. Significant frequencies of first-generation backcross genotypes were detected in two individual hybrid zone populations
(Berkeley and Monterey Marina) and in the hybrid zone as a whole, indicating that the potential exists for introgression between
M. galloprovincialis and M. trossulus. Despite this potential, we found no evidence of advanced introgression beyond first-generation backcrosses, suggesting that
gene flow between M. galloprovincialis and M. trossulus has been quite limited. The frequency of mussels with M. trossulus and hybrid genotypes declined abruptly south of Monterey Peninsula, while the frequency of mussels with M. galloprovincialis and hybrid genotypes declined precipitously north of Cape Mendocino. These abrupt genetic discontinuities indicate that this
blue mussel hybrid zone is presently positioned between two prominent coastal features and there is little, if any, export
of alleles from the hybrid zone into bordering parental populations.
Received: 20 August 1997 / Accepted: 26 October 1998 |
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