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The effectiveness of larval behavior in regulating transport between well-mixed, low-inflow estuaries and coastal waters in seasonally arid climates is poorly known. We determined the flux of an assemblage of benthic crustacean larvae relative to physical conditions between a shallow estuary and coastal waters on the upwelling coast of northern California (38°18′N, 123°03′W) from 29 to 31 March 2006. We detected larval behaviors that regulate transport in adjacent coastal waters and other estuaries for only two taxa in the low-inflow estuary, but they were apparent for taxa outside the estuary. Vertical mixing in the shallow estuary may have overwhelmed larvae of some species, or salinity fluctuations may have been too slight to cue tidal vertical migrations. Nevertheless, all larval stages of species that complete development in nearshore coastal waters were present in the estuary, because they remained low in the water column reducing seaward advection or they were readily exchanged between the estuary and open coast by tidal flows. Weak tidal flows and gravitational circulation at the head of the estuary reduced seaward transport during development for species that completed development nearshore, whereas larval release during nocturnal ebb tides enhanced seaward transport for species that develop offshore. Thus, nonselective tidal processes dominated larval transport for most species back and forth between the low-inflow estuary and open coastal waters, whereas in adjacent open coastal waters, larval behavior in the presence of wind-induced shear was more important in regulating migrations between adult and larval habitats along this upwelling coast. © 2014 Coastal and Estuarine Research Federation.

A new approach is introduced for the analysis of dispersal from the geographic distributions of mtDNA lineages. The method is based on the expected spatial distributions of lineages arising under a multigeneration random walk process. Unlike previous methods based on the predicted equilibria between genetic drift and gene flow, this approach is appropriate for non-equilibrium conditions, and yields an estimate of dispersal distance rather than dispersal rate. The theoretical basis for this method is examined, and an analysis of mtDNA restriction site data for Peromyscus maniculatus is presented as an example of how this approach can be applied to empirical data.

Using computer simulations, we generated and analyzed genetic distances among selectively neutral haplotypes transmitted through gene genealogies with random-mating organismal pedigrees. Constraints and possible biases on haplotype distances due to correlated ancestry were evaluated by comparing observed distributions of distances to those predicted from an inbreeding theory that assumes independence among haplotype pairs. Results suggest that: 1) mean time to common ancestry of neutral haplotypes can be a reasonably good predictor of evolutionary effective population size; 2) the nonindependence of haplotype paths of descent within a given gene genealogy typically produces significant departures from the theoretical probability distributions of haplotype distances; 3) frequency distributions of distances between haplotypes drawn from "replicate" organismal pedigrees or from multiple unlinked loci within an organismal pedigree exhibit very close agreement with the theory for independent haplotypes. These results are relevant to interpretations of current molecular data on genetic distances among nonrecombining haplotypes at either nuclear or cytoplasmic loci.

Spatial and temporal genetic heterogeneity in the sequences of nuclear protein-coding genes were investigated in populations of the blue crab, Callinectes sapidus. Haplotype frequencies of these novel markers were determined for adult crabs collected along 300 km in the northern Gulf of Mexico in two different years (2010 and 2011), as well as for megalopal recruits collected in 2010. Tests of genetic differentiation among all locations and between locations spanning known genetic breaks in other species were conducted. In addition, samples from distant locations within the range of C. sapidus were used to assess genetic divergence on a broader geographic scale. Significant between-year differences were found for adults at one location and near significant spatial differentiation was found across northern Gulf of Mexico locations in 2010. These results suggest that although the large population sizes and meroplanktonic life history of blue crabs promote widespread gene flow on a regional scale, genetic composition can change over just one year. Substantial divergence between the northern Gulf of Mexico and Venezuela suggests the possibility that temporal shifts in haplotype frequencies could result from variation in the rate of immigration from genetically distinct source populations. The possible effects of the Deepwater Horizon Oil Spill and attendant fisheries closures during the sampling phase of this study are also considered., Introduction Understanding the factors that determine connectivity among locations is essential for the management and conservation of marine populations (Gaines et al. 2003; Shaklee and Bentzen 1998). In particular, identification [...]

Clonal population structure in two marine sponges, Verongia longissimia and lotrochota birotulata, was examined with a self-recognition bioassay. The bioassay consists of grafts of branch segments between conspecific individuals. Results were consistent with the operational properties expected of a precise histocompatibility system. Autografts exhibited acceptance responses; grafts between individuals separated by large distances exhibited rejection responses; Individuals were not limited to a single mode of response at one time; and all identity relationships were transitive. Clonal population structure was assessed by examining the relationship between graft response and donor-to-recipient distance, and by actually mapping the distributions of particular clones. Clones of lotrochota birotulata were usually restricted to single coral heads or small patch reefs (1-3 m diameter). For Verongla longissima, which can grow directly upon the coral rubble surrounding coral heads and patch reefs, individual clones often occupied larger areas (up to 10 m diameter). The spatial patterns of clonal distributions are readily interpreted as consequences of the particular demographies and habitat specificitles of these two species. / 1983, American Genetic Association.

Random walk model facilitates the definition of probability conditions responsible for nonequilibrium geographic distributions of mtDNA lineages. Distance model predicts the variance of a mtDNA lineage geographic distribution as a function of age. A deviation of the lineage structure from equilibrium geographic patterning is observed during the analysis of mtDNA from natural populations.

The identification of genes involved in the adaptive evolution of non-model organisms with uncharacterized genomes constitutes a major challenge. This study employed a rigorous and targeted candidate gene approach to test for positive selection on protein-coding genes of the blue crab, Callinectes sapidus. Four genes with putative roles in physiological adaptation to environmental stress were chosen as candidates. A fifth gene not expected to play a role in environmental adaptation was used as a control. Large samples (n>800) of DNA sequences from C. sapidus were used in tests of selective neutrality based on sequence polymorphisms. In combination with these, sequences from the congener C. similis were used in neutrality tests based on interspecific divergence. In multiple tests, significant departures from neutral expectations and indicative of positive selection were found for the candidate gene trehalose 6-phosphate synthase (tps). These departures could not be explained by any of the historical population expansion or bottleneck scenarios that were evaluated in coalescent simulations. Evidence was also found for balancing selection at ATP-synthase subunit 9 (atps) using a maximum likelihood version of the Hudson, Kreitmen, and Aguadé test, and positive selection favoring amino acid replacements within ATP/ADP translocase (ant) was detected using the McDonald-Kreitman test. In contrast, test statistics for the control gene, ribosomal protein L12 (rpl), which presumably has experienced the same demographic effects as the candidate loci, were not significantly different from neutral expectations and could readily be explained by demographic effects. Together, these findings demonstrate the utility of the candidate gene approach for investigating adaptation at the molecular level in a marine invertebrate for which extensive genomic resources are not available. [ABSTRACT FROM AUTHOR]

The estimation of gene flow from the distribution of genetic markers in populations requires an indirect approach. Gene flow parameters are defined by demographic models, and population genetic models provide the link between these parameters and the distributions of genetic markers. Following the introduction of allozyme methods in the 1960s, a standard approach to the estimation of gene flow was developed. Wright's island model of population structure was used to relate the distribution of allozyme alleles in populations to Nem, the product of the effective population size and the rate of migration. Alternative strategies for the estimation of gene flow have been developed using different genetic markers, different models of demography and population genetics, and different methods of parameter estimation. No alternative strategy now available is clearly superior to the standard approach based on Wright's model and allozyme markers. However, this may soon change as methods are developed that fully utilize the genealogical relationships of DNA sequences. At present, alternative strategies do fill important needs. They can provide independent estimates of gene flow, measure different components of gene flow, and detect historical changes in population structure. [ABSTRACT FROM AUTHOR]

The dinoflagellate Hematodinium perezi is a prolific pathogen of the blue crab Callinectes sapidus along the Atlantic and Gulf of Mexico coasts of North America. High prevalence, sometimes approaching 100%, and outbreaks with high mortality are associated with higher salinities. H. perezi has not been reported previously in blue crabs from Louisiana, USA, where salinities in coastal habitats are generally below the parasite's favorable range. However, the possibility that H. perezi infects blue crabs in higher salinity habitats offshore has not been investigated. A PCR-based test for H. perezi was used to screen blue crabs collected from both high and low salinity areas. These included juvenile and adult crabs from inshore marshes where salinities are relatively low and from higher salinity offshore shoals that are spawning sites for females. H. perezi was detected in blue crabs from offshore shoals (prevalence=5.6%) but not in juvenile or adult crabs from inshore habitats. Megalopae (post-larvae) were also collected from inshore locations. Although megalopae settle inshore where salinities are relatively low, the megalopal stage is preceded by a planktonic phase in higher salinity offshore waters. We detected H. perezi in 11.2% of settling megalopae tested. Although the prevalence of H. perezi was relatively low within our samples, if spawning females and megalopae are especially vulnerable, the impact on the population could be compounded. This is the first report of H. perezi from blue crabs in Louisiana and demonstrates the importance of examining all life stages in determining the prevalence of a harmful parasite.