Effective population size (N e ) determines the strength of genetic drift in a population and has long been recognized as an important parameter for evaluating conservation status and threats to genetic health of populations. Specifically, an estimate of N e is crucial to management because it integrates genetic effectsPalabras Clave: deriva génica, metapoblación, método temporal, N e contempóranea, N e endogámica, N e varianza, proporción N e /N selección,suplementación basada en criaderos

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Understanding the barriers to genetic exchange in taxonomic groups that have a high dispersal potential will provide critical information on speciation in general. Blue rockfish (Sebastes mystinus) are good taxa to examine speciation because they are nonmigratory inhabitants of shallow rocky reef habitats along the eastern North Pacific with a pelagic larval stage lasting 3–5 months. The goal of this study was to analyse the evolutionary history and distribution patterns of different lineages within S. mystinus described previously and use this information to understand the speciation process in this group of high dispersal fish. The molecular data derived from specimens sampled over approximately 1650 km of the S. mystinus range revealed a northerly and southerly distribution for the two lineages. Almost equal frequencies of both lineages occurred at centrally located sample locations, with evidence of reproductive isolation between the lineages. A demographic analysis showed that the two lineages diverged and experienced sudden expansion prior to the last glacial maximum, which affected the observed pattern of genetic structure. The spatial distribution, demographic history and degree of genetic distinctiveness found from the genetic analysis, despite the high potential for dispersal in S. mystinus, suggest both lineages diverged in allopatry.

We examined the role of local adaptation in structuring the stable genetic step-cline of the eastern oyster Crassostrea virginica along an environmental gradient in the lagoon system of eastern Florida, USA. Reciprocally transplanted progeny, produced by a 10 × 10 genetic cross of wild brood stock from northern and southern genetic lineages yielded significant evidence of local adaptation (interaction of genes and environment) in variables related to fitness, including survival, wet meat weight, and reproductive maturation. The strength of local adaptation was asymmetric, with greater effects on the northern compared to the southern genetic lineage. To a lesser extent, we found evidence of both the role of environment (in particular, adverse effects on both genetic crosses in the southern region), and the role of genetic differences between the 2 crosses independent of environment, with higher initial growth of the southern genetic lineage and higher condition of the northern lineage. These differences suggest that maintenance of the genetic step-cline involves natural selection. We discuss the potential role of temperature and phytoplankton community composition between the northern and southern regions. Our study is the first to determine the genetic basis for fitness-related phenotypes, and to relate this to local adaptation of the eastern oyster. Understanding the role of the environment in structuring the eastern oyster throughout its range is critical for effective management, and the results of this study also suggest that small environmental changes may have significant effects on conservation of the eastern oyster, particularly in the northern genetic lineage.

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The spatial patterns of genetic structure among juveniles of long-lived species can reveal the extent of interannual and geographic variation in realized larval dispersal as well as the processes that determine ecologically relevant patterns of population connectivity. However, few studies examine this temporal and spatial variation over large portions of a species' geographic range or between cryptic species that overlap in their range. Despite the potential for long-distance dispersal in blue rockfish Sebastes mystinus, a previous study of adults revealed two geographically distinct, cryptic species. To determine year-to-year variation in the patterns of spatial connectivity and to elucidate the potential ecological mechanisms involved in shaping new yearclasses and maintaining cryptic species, we sampled juveniles within California, USA, where both cryptic species coexist. Using microsatellite markers, we found geographic and temporal variation in the number of individuals from these distinct cryptic species within 2 new year-classes of juvenile S. mystinus. We also found differences in the geographic patterns of genetic structure of the 2 cryptic species. Whereas one species exhibited little or no spatial genetic structure across the study region, the other exhibited a complex geographic pattern of genetic structure, with little or no genetic structure among regions, but small-scale structure within a region. The results of this study demonstrate that the spatial scales and patterns of realized dispersal of pelagic larvae vary geographically, interannually, and between closely related species with similar life-history strategies. Therefore, estimates of dispersal based on larval duration and patterns of adult structure need to be interpreted cautiously.