Introgression among three rockfish species (Sebastes spp.) in the Salish Sea, northeast Pacific Ocean.

Interspecific hybridization is often seen as a major conservation issue, potentially threatening endangered species and decreasing biodiversity. In natural populations, the conservation implications of hybridization depends on both on anthropogenic factors and the evolutionary processes maintaining the hybrid zone. However, the timeline and patterns of hybridization in the hybrid zone are often not known. Therefore, species conservation becomes a concern when recent anthropogenic changes influence hybridization and not if hybridization is part of a long-term process. Here, we use sequence data from one mitochondrial gene, three nuclear introns and one nuclear exon to estimate the direction, geographic extent, frequency and possible timeline of hybridization between three rockfish species (Sebastes auriculatus, S. caurinus, S. maliger) in the Salish Sea, Washington, USA. We show that (i) introgression occurred much more frequently in the Salish Sea than on the outer coast, (ii) introgression was highly asymmetrical from S. maliger into the other two species, (iii) almost 40% of individuals in the Salish Sea were hybrids, with frequency of hybrids increasing with isolation from the coast, and (iv) all hybrids were later generation backcrosses rather than F1 hybrids. Our results suggest long-standing low-level hybridization rather than recent onset of interbreeding because of human induced environmental change, possibly facilitated by specific environmental conditions in the sub-basins of the Salish Sea, and by differences in population sizes during recolonization of the area after the last glaciation. This rockfish hybrid system, with asymmetrical introgression and the maintenance of parental species, may prove useful to study both mechanisms that maintain species boundaries and that facilitate speciation in the presence of rapid environmental change.

Microsatellite Markers for Population Genetic Applications in the Domoic Acid-producing Diatom Pseudo-nitzschia australis Frenguelli (Bacillariophyceae).

Microsatellites are commonly used markers in population genetics and are increasingly being employed to determine population structure in phytoplankton populations. We have developed seven polymorphic microsatellite markers for the domoic-acid producing diatom Pseudo-nitzschia australis. Using these markers, thirty P. australis isolates were genotyped, 10 isolates were from Monterey Bay, California and 20 were from off the northern coast of Oregon. The number of alleles per locus ranged from two to eight and observed heterozygosities ranged from 0.11 to 0.70. All but two of the isolates were genetically distinct and initial population differentiation analysis indicated no significant differences between the Pacific Northwest isolates and the Monterey Bay isolates. Pseudo-nitzschia australis microsatellites appear to be species specific based on cross amplification tests with Pseudo-nitzschia fraudulenta (Cleve) Hasle, Pseudo-nitzschia seriata (Cleve) H.Peragallo, Pseudo-nitzschia pungens (Grunow ex Cleve) and Pseudo-nitzschia multiseries (Hasle) Hasle.