Genetic traits in the bivalve Mytilus from Europe, with an emphasis on Arctic populations

Genetic and some ecophysiological traits of mussels collected in the European Arctic, up to their northeastern distribution limit in the Barents Sea, were studied and compared with traits of mussels from the Mediterranean, Atlantic and Baltic. The genetic traits of these populations we-re analysed by isoenzyme electrophoresis on seven loci in order to assess the Mytilus complex to which populations in the Arctic region belong. Ecophysiological variables, the weight-index and glycogen were analysed to assess the physiological fitness of the populations. Three distinct groups were recognised: (1) Mytilus (edulis) galloprovincialis in the Mediterranean and Spain, (2) M. (edulis) edulis along the Atlantic coast from the Netherlands northwards into Russia, and (3) the Baltic Mytilus (edulis) trossulus. The mussels from populations in the Russian Arctic all belong to the Atlantic Mytilus (edulis) edulis group. The genetic variability and ecophysiological measures indicated that the sub-Arctic White Sea mussel populations have a relatively lower performance capacity, whereas those in the Arctic at the edge of their northern distribution showed a surprisingly strong performance. [KEYWORDS: Macoma-balthica; edulis-l; mussel populations; heterozygote deficiency; mercenaria-mercenaria; electrophoretic data; mitochondrial-dna; species complex; marine mollusks; genus mytilus]

Growth and longevity of Mytilus edulis (L.) from northeast Europe

The growth of mussels, Mytilus edulis (L.), was studied in most of the northeastern part of their distribution. The growth, longevity and maximal size of molluscs from 24 wild populations and one cultured population located in the White Sea and the southeast part of the Barents Sea were compared. The 25 studied populations were combined in six clusters. The maximal longevity and the size of the mussels varied between 7 and 18 years and 25.5 and 77.7 mm, respectively. The geographical location of the population within the studied region did not affect either maximal longevity or maximal size, or the growth rate of mussels. However, these parameters were influenced by local habitat conditions, primarily connected with the position within intertidal and subtidal zones. Animals inhabiting the intertidal zone were characterized by relatively low growth performance, a short life span and a small size. The longest life span was typical for deep subtidal mussels, whereas the highest growth rate was recorded in the cultured population and in the upper subtidal habitats. Growth patterns of Mytilus edulis in the subarctic White and the Arctic southeast Barents seas are similar to those reported from other parts of the area of distribution. Therefore, growth was mostly determined by local environmental factors, including those related to vertical zonation, rather than by latitude/longitude and related temperature effects

Growth and longevity of Mytilus edulis (L.) from northeast Europe

The growth of mussels, Mytilus edulis (L.), was studied in most of the northeastern part of their distribution. The growth, longevity and maximal size of molluscs from 24 wild populations and one cultured population located in the White Sea and the southeast part of the Barents Sea were compared. The 25 studied populations were combined in six clusters. The maximal longevity and the size of the mussels varied between 7 and 18 years and 25.5 and 77.7 mm, respectively. The geographical location of the population within the studied region did not affect either maximal longevity or maximal size, or the growth rate of mussels. However, these parameters were influenced by local habitat conditions, primarily connected with the position within intertidal and subtidal zones. Animals inhabiting the intertidal zone were characterized by relatively low growth performance, a short life span and a small size. The longest life span was typical for deep subtidal mussels, whereas the highest growth rate was recorded in the cultured population and in the upper subtidal habitats. Growth patterns of Mytilus edulis in the subarctic White and the Arctic southeast Barents seas are similar to those reported from other parts of the area of distribution. Therefore, growth was mostly determined by local environmental factors, including those related to vertical zonation, rather than by latitude/longitude and related temperature effects.

Growth in the bivalve Macoma balthica from its northern to its southern distribution limit: A discontinuity in North Europe because of genetic adaptations in Arctic populations?

The hypothesis was tested that towards a species limit of distribution its performance, such as growth or fitness, decreases. To this end, latitudinal changes in growth, maximum attainable length and genetic constitution were assessed for the Baltic clam, Macoma balthica (L.), at stations ranging from the most southern distribution limit (France) to its most north-eastern limit in the Arctic Pechora Sea (North Russia). Growth was analyzed by means of growth-rings on the shells, the genetic constitution by electrophoretic isoenzyme analysis. Growth patterns and the genetic constitution of populations from West Europe, North Europe and the White Sea were similar, whereas the populations from the Pechora Sea are distinct from the other populations. The performance of clams in the Pechora Sea populations, with a relatively low annual growth but high maximum length, was, in contrast to the hypothesis, not decreased. It is concluded that the Pechora Sea populations form a separate group, genetically different from other European populations and adapted to the Arctic conditions. [KEYWORDS: Arctic; adaptation; distribution limit; genetics; geographic cline; growth; Macoma balthica; shell-length Dutch wadden sea; electrophoretic data; recruitment; gironde; stress

Growth in the bivalve Macoma balthica from its northern to its southern distribution limit: A discontinuity in North Europe because of genetic adaptations in Arctic populations?

The hypothesis was tested that towards a species limit of distribution its performance, such as growth or fitness, decreases. To this end, latitudinal changes in growth, maximum attainable length and genetic constitution were assessed for the Baltic clam, Macoma balthica (L.), at stations ranging from the most southern distribution limit (France) to its most north-eastern limit in the Arctic Pechora Sea (North Russia). Growth was analyzed by means of growth-rings on the shells, the genetic constitution by electrophoretic isoenzyme analysis. Growth patterns and the genetic constitution of populations from West Europe, North Europe and the White Sea were similar, whereas the populations from the Pechora Sea are distinct from the other populations. The performance of clams in the Pechora Sea populations, with a relatively low annual growth but high maximum length, was, in contrast to the hypothesis, not decreased. It is concluded that the Pechora Sea populations form a separate group, genetically different from other European populations and adapted to the Arctic conditions. [KEYWORDS: Arctic; adaptation; distribution limit; genetics; geographic cline; growth; Macoma balthica; shell-length Dutch wadden sea; electrophoretic data; recruitment; gironde; stress]

Sensitivity to stress in the bivalve Macoma balthica from the most northern (Arctic) to the most southern (French) populations: low sensitivity in Arctic populations because of genetic adaptations?

The stress sensitivity, determined in copper exposure experiments and in survival in air tests, and the genetic structure, measured by means of isoenzyme electrophoresis, were assessed in populations of the Baltic clam Macoma balthica (L.) from its southern to its northern distribution limit, in order to test the hypotheses that near the distribution limit the clams would be more stress sensitive and would have a lower genetic variability. The populations in west and north Europe show a strong genetic resemblance. The populations in the sub- Arctic White Sea are genetically slightly different, and show a low stress sensitivity. The populations in the Arctic Pechora Sea are genetically very distant from the other populations, and show the lowest stress sensitivity. Near the southern distribution limit, in agreement with the hypotheses, genetic variability is low and stress sensitivity high. On the other hand, in contrast to expectation, near the northern distribution limit, in the populations of the Pechora Sea, the genetic variability was higher, thus not reduced, and the stress sensitivity was low compared to ail other populations. Yet, it remains a question if such is due to gradual physiological acclimatization (and ongoing differential selection) or to genetic adaptation. [KEYWORDS: Arctic; adaptation; copper; distribution limit; genetics geographic cline; Macoma balthica; stress sensitivity; survival in air Allele frequency cline; mussel mytilus-edulis; crassostrea-virginica; electrophoretic data; allozyme variation; marine mollusks; differentiation; selection; growth; oyster]