No abstract

No abstract

Two size groups (20-30 and 45-55 mm) of Mytilus edulis and Mytilus taossulus were assessed from May to December 1992 at two locations in Nova Scotia. The two species were classified using electrophoresis based on mannose phosphate isomerase, and a discriminant function based on shell morphornetry. The discriminant function misclassified less than 5% sf the mussels and of these, 1% of the M. edulis were rnisclassified as M. taossulus, and 10% of the Me tros.sulus were rnisclassified as M. sdulis. In general, both size groups of M edulis tended to have higher shell growth rates than M. trossulus. Overall mortality was 6% and occurred primarily from mid-August to mid-September; M. edulis exhibited a slightly lower survival and for a given shell length had a higher average tissue and shell weight, as well as a greater shell height, than M. trossulus. Mytilus tasssulus had a significantly lower tissue weight during the summer and was eliminated at a significantly higher rate during commercial grading trials than M. edulis. We estimated from the information on individual weight, survival, and grading losses that the economic value of M. edulis was 8.7 times higher than that of M. tasssulus. RCsnmC: Nous avons Cvaluk deux groupes de taille (20-30 et 45-55 mm) de Mytilus edulis et de Mytllus trmsulus, de mai h dkcembre 1992, B deux endroits de la ~ouvelle-lhosse. Nous avons sCparC les deux espkces par Clectrophorisse & partir de la phospho-mannose-isomerase et par une fonction discriminante fondCe sur la morphomCtrie de la coquille : la fonction discriminante a ma8 class6 moins de 5% des moules et, parmi celles-ci, 1% des M. edralis ont Ct6 classkes ii tort comme les M. trossulus, tandis que 18% des M. trossulus ont CtC classCes comme les M. sdulis. De fagon gCnCrale, dam lies deux groupes Be taille, M. edulis presentait un taux de crsissance de la coquille plus ClevC que M. taossulus. La mortalit6 Ctait globalement de 6%; elle se produisait surtout de la mi-aoiat B la mi-septembre; Mytilus edulis prksentait un taux de survie lCg2rernent plus bas et, pour une longueur de coquille QsnnCe, avait un poids moyen de tissus et de coquille plus klevC, ainsi qaa'une hauteur de coquille plus grande que Ma trossulus. Mytilus trossulus avait pendant l'Ct6 un poids de tissus significativement plus bas et a 6tC 6liminCe pendant les essais de tri commercial 2 un rythme significativement plus ClevC que M. edulis. A partir de I'information sur le poids individuel, la survie et les pertes au tri, nous estimons que la vaBeur Cconomique de M* edulis est E,7 fois plus ClevCe que celle de M. trossulus. [Traduit par la Redaction] Several studies have established the presence of two species of blue mussels, Mytilus edulis and Mytilus trsssulus, in certain regions of Atlantic Canada (Varvio et al. 1988; McDonald et al. 1992; Gosling 1993). Specifically, mixed populations of the two species with varying proportions are a common occurrence along the Atlantic coast sf Nova Scotia, in Newfoundland, and dong the upper reaches of the Gulf of St. Lawr...

No abstract

In a natural population of two-year-old mussels, shell length was correlated with degree of heterozygosity. There was no correlation between an individual's glycogen level and its degree of heterozygosity, but when individuals were grouped in heterozygosity classes a near-significant correlation was observed between degree of heterozygosity and mean glycogen level corrected for the effects of sex and stage of gonad development. There was no correlation between degree of heterozygosity and index of gonad development. Such a correlation would have provided support for the hypothesis (Zouros and Foltz, 1984) that dependence of time of spawning on heterozygosity may explain the observed heterozygote-deficiency. The causes of heterozygote-deficiency, a common phenomenon in populations of marine bivalves, remain obscure. The observed heterozygosity-growth correlation is examined in the light of the controversy of whether allozymes act as markers in linkage association with genetic conditions that are responsible for the differences in growth among individuals or are themselves the agents of the correlation. The observations that 1) the contributions of individual loci to the correlation vary among populations, 2) the correlation is observed in samples from natural populations but not among progeny from pair matings, and 3) the correlation is nearly always accompanied with heterozygote-deficiency in the population are more compatible with the first explanation and suggest that the growth-heterozygosity correlation results mostly from associative overdominance and to a lesser extent from the direct contributions of scored loci to growth.

No abstract

No abstract

No abstract