Analysis of individual year-classes of a marine fish reveals little evidence of first-generation hybrids between cryptic species in sympatric regions |
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Authors: | Martha O Burford Giacomo Bernardi Mark H Carr |
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Institution: | (1) Department of Ecology and Evolutionary Biology, University of California Santa Cruz, 100 Shaffer Road, Santa Cruz, CA 95060, USA;(2) Present address: Department of Biology, University of Central Oklahoma, 100 North University Drive, Edmond, OK 73034, USA |
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Abstract: | As settled juveniles and adults, blue rockfish (Sebastes mystinus) are nonmigratory inhabitants of kelp and rocky reef habitats along the California coast, USA, and prior to settlement, they
possess a pelagic larval and juvenile stage lasting 3–5 months. A previous study of adults revealed two cryptic species within
S. mystinus and evidence of reproductive isolation in a region where both cryptic adults co-occur. Given this pattern of reproductive
isolation, we investigated the degree of hybridization or introgression in individual year-classes shortly after juvenile
settlement in two different years (2001 and 2002). Using microsatellite markers, we found little indication of hybridization
in new juvenile year-classes despite an adult population that comprised both cryptic species. However, we found an average
of two percent of hybrid or introgressed individuals in regions with a low frequency of one of the two species. Therefore,
while the lack of hybrids or introgression supports the hypothesis of reproductive isolation between the cryptic species within
S. mystinus, the age-structured analysis also revealed a spatial pattern of low-frequency differences in the number of introgressed individuals.
These results suggest that reproductive barriers may breakdown when one of the two species predominates the regional adult
gene pool. |
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