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Genetic differences among natural populations of the blue mussel (Mytilus edulis) appear to have implications for commercial exploitation of the species. Growth and mortality patterns in transplanted versus resident wild stocks presented here verify that the genetic differences among populations involve the production parameters. Hatchery produced juveniles from various populations outplanted at different sites showed different mean growth rates depending on parent stock. These observations suggest there are adaptations to local conditions and underscore the need for careful selection by the mariculturist of both site and source of seed stock.

In animals, mitochondrial DNA (mtDNA) inheritance is predominantly maternal. In a few cases incidental transmission of paternal mtDNA was observed and estimated to account for only 10(-4)-10(-3) of an individual's mtDNA content. In contrast, biparental inheritance is common in mussels of the genus Mytilus. Here we present direct evidence that sex and mtDNA inheritance are coupled in Mytilus. Females inherit mtDNA only from their mother, but they transmit it to both daughters and sons. Males inherit mtDNA from both parents, but they transmit to sons only the mtDNA they inherited from their father. In pair matings, this mtDNA inheritance pattern is associated with a strong sex-ratio bias. These findings establish a newly discovered type of cytoplasmic DNA transmission. We also present evidence that the phenomenon breaks down in interspecific hybrids.

High-elevation valleys in dry areas of the Himalayas are among the most extreme, yet least explored environments on Earth. These barren, rocky valleys are subjected to year-round temperature fluctuations across the freezing point and very low availability of water and nutrients, causing previous workers to hypothesize that no photoautotrophic life (primary producers) exists in these locations. However, there has been no work using modern biogeochemical or culture-independent molecular methods to test the hypothesis that photoautotrophs are absent from high Himalayan soil systems. Here, we show that although microbial biomass levels are as low as those of the Dry Valleys of Antarctica, there are abundant microbial photoautotrophs, displaying unexpected phylogenetic diversity, in barren soils from just below the permanent ice line of the central Himalayas. Furthermore, we discovered that one of the dominant algal clades from the high Himalayas also contains the dominant algae in culture-independent surveys of both soil and ice samples from the Dry Valleys of Antarctica, revealing an unexpected link between these environmentally similar but geographically very distant systems. Phylogenetic and biogeographic analyses demonstrated that although this algal clade is globally distributed to other high-altitude and high-latitude soils, it shows significant genetic isolation by geographical distance patterns, indicating local adaptation and perhaps speciation in each region. Our results are the first to demonstrate the remarkable similarities of microbial life of arid soils of Antarctica and the high Himalayas. Our findings are a starting point for future comparative studies of the dry valleys of the Himalayas and Antarctica that will yield new insights into the cold and dry limits to life on Earth.

To investigate the influence of genetics and environment on the growth of Mytilus edulis at low temperatures, we transplanted juveniles from 11 stocks to 10 sites along the coast of Nova Scotia, Canada. For each stock at each site, the mean change in shell length, dry shell weight, dry tissue weight and viability from early November 1985 to mid-April 1986 were documented. Stock and site differences were important in explaining the variance in shell growth (length and weight) but site alone accounted for most of the variation in tissue growth. Tissue growth was higher at ice-free sites than at ice-covered sites, but shell growth was similar among sites. We speculate that tissue growth was food-limited at those sites where ice-coverage delayed the onset of the spring phytoplankton bloom.

Juveniles of the blue mussel Mytilus edulis that had resulted from a large number of pair matings were examined at six polymorphic enzyme loci. In four loci, the overall number of heterozygotes was significantly less than expected from the parental genotypes. The degree of deviation from expectation varied considerably among families, and families which shared the same male parent tended to show similar degrees of deviation. Inbreeding and population mixture, the two most cited explanations of heterozygote deficiency (a phenomenon commonly observed in populations of marine bivalves), do not apply in the case of pair-matings, and the null allele hypothesis is inconsistent with the data. These observations suggest that genotype-dependent larval mortality constitutes the most probable cause of this phenomenon.

Comparative production estimates of selected species may provide indices of environmental quality, but so far there is little information on the extent to which production responses are mediated by genotypes. This study used a single source stock of blue mussels (Mytilus edulis) to explore differences between two bays. Test animals were held in suspension for 20 mo and growth and mortality observations of size-groups and of identified individuals were made at biweekly intervals. Average growth rates differed slightly between bays but mortality differences were marked and were the principle determinants of net production differences between the bays. Observed growth rates differed markedly between individuals but showed a striking consistency within individuals, indicative of genetic influence on this parameter. Because both mortality and growth interact with body size and season, it is clear that the estimated production levels and differences between bays would be influenced by the mixture of genotypes. We conclude that growth and mortality measures of M. edulis could provide sensitive environmental indices, but growth types in the test stock would need to be standardized. Key words: mussel; growth, mortality; environmental indices; genetic influence

Shell length and electrophoretic heterozygosity at six enzyme loci were scored in juveniles of 30 hatchery-grown families and in adults of 10 field-grown families of the blue mussel Mytilus edulis. A total of 4 809 offspring were scored. We found no consistent pattern in the correlations between shell length and enzyme heterozygosity among sibs within families. However, a significant family effect on shell length was observed, suggesting an influence of background genotype on this character. A family effect on viability was also observed. When the environment and family effects were accounted for, a small positive correlation between heterozygosity and shell length at the juvenile stage remained. This correlation was significant in one of the three experiments. No such correlation was evident at the adult stage. Our interpretation of these results is that electrophoretic alleles appear to have no direct of independent effect of their own on growth. We suggest that the negative correlation of homozygosity with these characters, seen in natural populations, results from homozygosity for hidden recessive deleterious genes with which the electromorphs are in a steady state of quasilinkage disequilibrium.

Genetic differences among Mytilus edulis populations from four localities in Atlantic Canada were examined using electrophoretic techniques. On the basis of allele frequency distributions at four loci (LAP-1, PEPTIDASE-2, PGI, PGM), the localities fell into two pairs, paralleling a similar pairing on the basis of values of specific environmental parameters and their variability. Gene flow between environments could be eliminated as an explanation of gene frequency similarity in one of the pairs. The large heterozygote deficiencies appear not to be satisfactorily explained by the Wahlund effect, inbreeding, or "silent alleles," without the added influence of environmental selection. We conclude that the allele frequency patterns reflect differences in the average environmental characteristics among localities.Key words: isoenzymes, blue mussels, genetic differences, environmental selection, Mytilus edulis

Reciprocal transfers of three blue mussel (Mytilus edulis) stocks among three rearing sites resulted in marked changes in growth, mortality, and maximum biomass. Results indicate that site differences were major determinants of the growth effects, while stock differences were chiefly responsible for the mortality effects. The overall effect on biomass and potential yield was approximately equally attributable to site and stock influences. The results have relevance to aquaculture and environmental assessment using mussels and illustrate genotypic responses that may be significant for fisheries management.

There are significant genetic differences among populations of the blue mussel, Mytilus edulis, from six localities in St. Margaret's Bay, N.S., Canada, despite the presence of gene flow. The populations are differentiated into two groups, those at the head of the bay where ambient conditions fluctuate widely during the year, and those at the mouth of the bay where conditions (particularly salinity) fluctuate to a lesser degree. Three isoenzyme loci, i.e. leucine aminopeptidase 1, peptidase 2, and phosphoglucose mutase, show a clear shift in the predominant frequencies, from slow migrating alleles at the mouth of the bay to faster migrating alleles at the head of the bay. This shift is a microgeographic parallel of the pattern we observed in 1980 on a macrogeographic scale. A genetic comparison of these populations with those studied previously shows that allele "populations" cluster according to their environment and not according to geographical proximity. We conclude that differences in allele frequencies among localities index heterogeneity among environmental conditions, and that the sensitivity to environmental selective forces varies from locus to locus.

Estimates of genetic parameters in bivalves have typically been based on few families and are limited to larval and juvenile characters. Using mussels from a natural population, 30 replicated families were reared to an average size of 8 mm in the laboratory and subsequently in two natural environments. The effects of rearing full-sibs apart from fertilization and from day 55 have been estimated for adult shell length. Heritabilities were calculated from the sire and dam variance components for mussels up to an average size of 30 mm. In general, the heritabilities for directional were moderate to large, suggesting the possibilities of rapid genetic changes under directional selection. For survival, the additive genetic variance was zero or non-significant. However, the dam component was very large which suggests the presence of either important maternal or non-additive gene effects.

To investigate environmental and seasonal patterns of mortality among natural populations of the blue mussel, Mytilus edulis, we transplanted 11 stocks of juvenile mussels to nine sites along the coast of Nova Scotia, Canada. Stock, Stock by Site, and Stock by Season together accounted for 53% of the variance in mortality whereas Site and Season together explained less than 1% of the variance. Genetic variability among stocks was inferred from differences in their cumulative mortality averaged over all environments. Several stocks, however, exhibited similar levels of mortality over all sites and were apparently insensitive to the environmental gradient. This implies physiological flexibility or the ability to tolerate a wide range of environmental conditions. We conclude that the blue mussel adapts to variable environments by maintaining both physiologically flexible and genetically variable populations. In addition, we noted that stocks originating from more stressful environments tended to exhibit lower mortalities than those originating from less stressful environments.