Pattern and scale of geographic variation in environmental sex determination in the Atlantic silverside, Menidia menidia.

The Atlantic silverside, Menidia menidia (Pisces: Atherinidae), exhibits an exceptionally high level of clinal variation in sex determination across its geographic range. Previous work suggested linear changes in the level of temperature-dependent sex determination (TSD) with increasing latitude. Based on comparisons at 31 sites encompassing the entire species' range, we find that the change in level of TSD with latitude is instead highly nonlinear.

A new PCR-based method shows that blue crabs (Callinectes sapidus (Rathbun)) consume winter flounder (Pseudopleuronectes americanus (Walbaum)).

Winter flounder (Pseudopleuronectes americanus) once supported robust commercial and recreational fisheries in the New York (USA) region, but since the 1990s populations have been in decline. Available data show that settlement of young-of-the-year winter flounder has not declined as sharply as adult abundance, suggesting that juveniles are experiencing higher mortality following settlement. The recent increase of blue crab (Callinectes sapidus) abundance in the New York region raises the possibility that new sources of predation may be contributing to juvenile winter flounder mortality.

Severe inbreeding and small effective number of breeders in a formerly abundant marine fish.

In contrast to freshwater fish it is presumed that marine fish are unlikely to spawn with close relatives due to the dilution effect of large breeding populations and their propensity for movement and reproductive mixing. Inbreeding is therefore not typically a focal concern of marine fish management. We measured the effective number of breeders in 6 New York estuaries for winter flounder (Pseudopleuronectes americanus), a formerly abundant fish, using 11 microsatellite markers (6-56 alleles per locus).

The response of correlated traits following cessation of fishery-induced selection.

The application of evolutionary principles to the management of fisheries has gained considerable attention recently. Harvesting of fish may apply directional or disruptive selection to key life-history traits, and evidence for fishery-induced evolution is growing. The traits that are directly selected upon are often correlated (genetically or phenotypically) with a suite of interrelated physiological, behavioral, and morphological characters.

Spatial scale and divergent patterns of variation in adapted traits in the ocean.

The geography of adaptive genetic variation is crucial to species conservation yet poorly understood in marine systems. We analyse the spatial scale of genetic variation in traits that broadly display adaptation throughout the range of a highly dispersive marine species. We conducted common garden experiments on the Atlantic silverside, Menidia menidia, from 39 locations along its 3000 km range thereby mapping genetic variation for growth rate, vertebral number and sex determination.

Regional differentiation and post-glacial expansion of the Atlantic silverside, an annual fish with high dispersal potential.

The coastal marine environment of the Northwest Atlantic contains strong environmental gradients that create distinct marine biogeographic provinces by limiting dispersal, recruitment, and survival. This region has also been subjected to numerous Pleistocene glacial cycles, resulting in repeated extirpations and recolonizations in northern populations of marine organisms. In this study, we examined patterns of genetic structure and historical demography in the Atlantic silverside, an annual marine fish with high dispersal potential but with well-documented patterns of clinal phenotypic adaptation along the environmental gradients of the Northwest Atlantic.

The covariance between genetic and environmental influences across ecological gradients: reassessing the evolutionary significance of countergradient and cogradient variation.

Patterns of phenotypic change across environmental gradients (e.g., latitude, altitude) have long captivated the interest of evolutionary ecologists.