Assessment of natural selection in a hybrid population of mussels: evaluation of exogenous vs endogenous selection models |
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Authors: | R Wilhelm 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: | We examined natural selection within a population of marine mussels, sampled in southwestern England in June 1991, containing
a high frequency of hybrids between Mytilus edulis L. and M. galloprovincialis Lmk. This system is particularly tractable for the assessment of natural selection because hybridization is common and individual
mussels can be aged, allowing changes in the frequency of hybrid genotypes among age classes to be determined. We show that
strong viability selection occurs among hybrid genotypes which results in the virtual elimination of M. edulis–like genotypes from the population over a period of 3 years. Recombinant hybrid genotypes are intermediate in fitness, with
M. edulis–like genotypes having a lower survival rate and M. galloprovincialis–like genotypes having a higher survival rate than genotypes of mixed ancestry. Since intermediate fitness for hybrid genotypes
is inconsistent with endogenous selection models we conclude that the structure and position of this hybrid zone is probably
generated by exogenous selection. This pattern of selection is a recurring feature of this hybrid population and likely occurs
elsewhere in the hybrid zone. Selection against M. edulis–like genotypes appears to be offset by extensive immigration of larvae dispersed from pure populations of M. edulis.
Received: 14 July 1997 / Accepted: 24 February 1998 |
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