Integration of natural selection across the life cycle stabilizes a marine mussel hybrid zone.

Hybridization among related species is now recognized as common but it remains unclear how hybrid zones persist for prolonged periods. Here, we test the hypothesis that selection in different components of the life cycle may stabilize a hybrid zone. A hybrid zone occurs in southwest England between the marine mussels and .

Long-term, high frequency in situ measurements of intertidal mussel bed temperatures using biomimetic sensors.

At a proximal level, the physiological impacts of global climate change on ectothermic organisms are manifest as changes in body temperatures. Especially for plants and animals exposed to direct solar radiation, body temperatures can be substantially different from air temperatures. We deployed biomimetic sensors that approximate the thermal characteristics of intertidal mussels at 71 sites worldwide, from 1998-present.

Loss of thermal refugia near equatorial range limits.

This study examines the importance of thermal refugia along the majority of the geographical range of a key intertidal species (Patella vulgata Linnaeus, 1758) on the Atlantic coast of Europe. We asked whether differences between sun-exposed and shaded microhabitats were responsible for differences in physiological stress and ecological performance and examined the availability of refugia near equatorial range limits. Thermal differences between sun-exposed and shaded microhabitats are consistently associated with differences in physiological performance, and the frequency of occurrence of high temperatures is most probably limiting the maximum population densities supported at any given place.

Climate change, species distribution models, and physiological performance metrics: predicting when biogeographic models are likely to fail.

Modeling the biogeographic consequences of climate change requires confidence in model predictions under novel conditions. However, models often fail when extended to new locales, and such instances have been used as evidence of a change in physiological tolerance, that is, a fundamental niche shift. We explore an alternative explanation and propose a method for predicting the likelihood of failure based on physiological performance curves and environmental variance in the original and new environments.

Physiological energetics and biogeographic range limits of three congeneric mussel species.

Closely related species with different physiological tolerances and distributions make ideal systems for documenting range shifts in response to a changing climate. Mytilus edulis, M. trossulus, and M.

Ecological genetics in the North Atlantic: environmental gradients and adaptation at specific loci.

The North Atlantic intertidal community provides a rich set of organismal and environmental material for the study of ecological genetics. Clearly defined environmental gradients exist at multiple spatial scales: there are broad latitudinal trends in temperature, meso-scale changes in salinity along estuaries, and smaller scale gradients in desiccation and temperature spanning the intertidal range. The geology and geography of the American and European coasts provide natural replication of these gradients, allowing for population genetic analyses of parallel adaptation to environmental stress and heterogeneity.

Patterns of larval dispersal and their effect on the maintenance of a blue mussel hybrid zone in southwestern England.

The blue mussels Mytilus edulis and M. galloprovincialis hybridize in southwestern England. Within this hybrid zone environmentally based directional selection favors individuals with alleles specific to M.

ASYMMETRIC INTROGRESSION OF MITOCHONDRIAL DNA AMONG EUROPEAN POPULATIONS OF BLUE MUSSELS (MYTILUS SPP.).

-Mytilus edulis and M. galloprovincialis are two blue mussel species that coexist in western Europe. Previously, we reported that M.

GENETICS OF PHYSIOLOGICAL DIFFERENTIATION WITHIN THE MARINE MUSSEL GENUS MYTILUS.

Two divergent taxa in the marine mussel genus Mytilus are largely isolated geographically and are routinely exposed to distinctly different thermal environments. We tested the hypothesis that the two taxa are physiologically differentiated with respect to temperature and examined the evolved adaptations allowing one of the taxa to exploit habitats where warm-temperate conditions prevail for prolonged periods. We first analyzed the physiological response to high temperature of mussels collected from a hybrid population containing members of both pure taxa, F, hybrids, and a variety of introgressed genotypes.

GENOTYPE-ENVIRONMENT INTERACTION FOR JUVENILE GROWTH IN THE HARD CLAM MERCENARIA MERCENARIA (L.).

Offspring from half-sib and full-sib families of the hard clam, Mercenaria mercenaria were reared in five locations along the Atlantic Coast to test for the presence of genotype-environment interaction for juvenile growth rate. Location effects upon growth rate variation were prevalent; of the genetic effects, the additive genetic by location variance was predominant with the nonadditive genetic by location component contributing to a lesser degree to the interaction variance. The additive and nonadditive variation over all environments was negligible.

QUANTITATIVE GENETICS OF JUVENILE GROWTH AND SHAPE IN THE MUD CRAB EURYPANOPEUS DEPRESSUS 1.

Rates of growth and development were measured for the first six molts following the crab 1 stage in the mud crab Eurypanopeus depressus. The genetic contribution to variation in growth rate, development rate, and shape was determined for each molt interval. Genetic variation in growth rate, measured as increases in both width and length, was evident at most molt intervals.

THE PHYSIOLOGICAL BASIS OF NATURAL SELECTION AT THE LAP LOCUS.

An extensive research program was undertaken to evaluate the contribution of genetic variation at the Lap locus to variation in physiological traits under natural conditions. Rates of carbon and nitrogen metabolism were monitored in a population of the mussel Mytilus edulis near the center of the Lap allele frequency cline on the north shore of Long Island. The goal of this research was to establish whether the previously described genotype-dependent differences in physiological phenotype are meaningful in ecologically relevant circumstances.

EXCLUSION OF THE ROLE OF SECONDARY CONTACT IN AN ALLELE FREQUENCY CLINE IN THE MUSSEL MYTILUS EDULIS.

We examined the hypothesis that secondary contact generates an allele-frequency cline at the aminopeptidase-I locus (Lap) in the marine mussel, Mytilus edulis. It has been proposed that variation at the Lap locus is neutral and that the cline results from secondary contact between differentiated oceanic and estuarine populations (Levinton, 1980). We tested this hypothesis by comparing the genotypic distributions in samples from the cline to distributions that incorporate mixing effects.