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Comparative growth and survival patterns of Mytilus trossulus and Mytilus edulis in Atlantic Canada
Canadian Journal of Fisheries and Aquatic Sciences
Abstract and Figures
Two size groups (20–30 and 45–55 mm) of Mytilus edulis and Mytilus trossulus 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 morphometry. The discriminant function misclassified less than 5% of the mussels and of these, 1% of the M. edulis were misclassified as M. trossulus, and 10% of the M. trossulus were misclassified as M. edulis. 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 trossulus 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 1.7 times higher than that of M. trossulus.
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... A cryptic presence of M. trossulus in M. edulis plantations in Loch Etive (Scotland) in the 2000s resulted in significant production losses because M. trossulus had lower consumer properties and shells too fragile for harvesting and grading [19,20]. Considerable differences between species were also found in Canadian aquaculture [8,21], where the commercial value of M. trossulus was estimated to be 1.7 times less than that of M. edulis [8]. The difficulty of identifying M. edulis and M. trossulus by the shells is frustrating, and any cue for distinguishing these species in sympatry without genotyping would be a welcome addition to the toolkit of mussel studies. ...
... A cryptic presence of M. trossulus in M. edulis plantations in Loch Etive (Scotland) in the 2000s resulted in significant production losses because M. trossulus had lower consumer properties and shells too fragile for harvesting and grading [19,20]. Considerable differences between species were also found in Canadian aquaculture [8,21], where the commercial value of M. trossulus was estimated to be 1.7 times less than that of M. edulis [8]. The difficulty of identifying M. edulis and M. trossulus by the shells is frustrating, and any cue for distinguishing these species in sympatry without genotyping would be a welcome addition to the toolkit of mussel studies. ...
... Should the latter prove true, the morphotype test would facilitate local mussel studies in the Atlantic. Since interspecific differences in this particular character were overlooked in previous morphometric studies, which all were based on references from outside of the White Sea [7][8][9][10], it remains possible that this difference is indeed valid only in the White Sea. Such a situation could be associated with the unusual environment, featuring a combination a subarctic climate and a relatively low salinity (< 25 ppt- [25]) and/or with the history of the local M. trossulus. ...
Cryptic and hybridizing species may lack diagnostic taxonomic characters leaving researchers with semi-diagnostic ones. Identification based on such characters is probabilistic, the probability of correct identification depending on the species composition in a mixed population. Here we test the possibilities of applying a semi-diagnostic conchological character for distinguishing two cryptic species of blue mussels, Mytilus edulis and M. trossulus. These ecologically, stratigraphically and economically important molluscs co-occur and hybridize in many areas of the North Atlantic and the neighboring Arctic. Any cues for distinguishing them in sympatry without genotyping would save much research effort. Recently these species have been shown to statistically differ in the White Sea, where a simple character of the shell was used to distinguish two mussel morphotypes. In this paper, we analyzed the associations between morphotypes and species-specific genotypes based on an abundant material from the waters of the Kola Peninsula (White Sea, Barents Sea) and a more limited material from Norway, the Baltic Sea, Scotland and the Gulf of Maine. The performance of the “morphotype test” for species identification was formally evaluated using approaches from evidence-based medicine. Interspecific differences in the morphotype frequencies were ubiquitous and unidirectional, but their scale varied geographically (from 75% in the White Sea to 15% in the Baltic Sea). In addition, salinity-related variation of this character within M. edulis was revealed in the Arctic Barents Sea. For every studied region, we established relationships between the proportions of the morphotypes in the populations as well as between the proportions of the morphotypes in samples and the probabilities of mussels of different morphotypes being M. trossulus and M. edulis. We provide recommendations for the application of the morphotype test to mussels from unstudied contact zones and note that they may apply equally well to other taxa identified by semi-diagnostic traits.
... Further, derived discriminate functions have recorded the significant association between all the shell characteristics in the predicted model of current study. Previous study conducted by Mallet and Carver (1995) [15] , have developed the higher correlation for the shell height (ranged at 39 -43 mm of shell height) instead of shell length in the predicted model produced for identification of morphological differences of Mytilus edulis and Mytilus trossulus bivalve species from Nova Scotia, Atlantic Canada, revealing that shell height is an important parameter in the assessment of morphological characters of bivalves. Thus, shell based morphological parameters (shell length, width and height) act as effective tool in providing precise, accurate and reliable information to identify morphological difference of bivalve populations. ...
... Further, derived discriminate functions have recorded the significant association between all the shell characteristics in the predicted model of current study. Previous study conducted by Mallet and Carver (1995) [15] , have developed the higher correlation for the shell height (ranged at 39 -43 mm of shell height) instead of shell length in the predicted model produced for identification of morphological differences of Mytilus edulis and Mytilus trossulus bivalve species from Nova Scotia, Atlantic Canada, revealing that shell height is an important parameter in the assessment of morphological characters of bivalves. Thus, shell based morphological parameters (shell length, width and height) act as effective tool in providing precise, accurate and reliable information to identify morphological difference of bivalve populations. ...
... However, previous studies have recorded the intra-specific morphological variability of shellfish populations based on the sampling locations [4,16,32] . Shell height of Mytilus sp. is significantly different with sampling locations, due to the environmental differences in respective intertidal habitats (p<0.05) have identified [15] . As revealed by Gardener (1996) [8] , the model developed by Canonical Discriminant Analysis (CDA) for predicting morphological variations of mussels has failed to distinguish morphometric differences even between Mytilus edulis, Mytilus galloprovincialis due to significant proportion of hybrid mussel varieties within the zone. ...
The present study was focused on assessment of morphological variations of clam in Mannar lagoon, Sri Lanka. A total of 150 individual clams (fifty individuals per each site; Naruvilikkulam, Achchankulam and Mutharipputhurai) were collected from June to November 2017 and subjected to Discriminant Function Analysis (DFA) using morphometric parameters to identify intra-specific morphological variation. Length-weight relationship and condition factor were assessed for 3 Clam groups. Average shell length, shell height, length and width of hinge plate, and total weight of clams ranged at 47.30-52.40, 39.60-43.92, 23.41-26.37, 8.83-10.34 mm and 35.80-51.20 g respectively. Predicted model of DFA derived 99.8% and 0.2% of variances for function 1 and 2 respectively. All 3 Clam groups had negative allometric growth pattern (b= <3). Average condition factor (K) calculated for this species was 0.036 indicating unfavorable factors in living habitats. Basic morphological information of Clams is useful in aquaculture and fisheries sector of Sri Lanka.
... Mussels can be identified by two methods: allozyme analysis or by morphometric measurement combined with statistical analysis (McDonald et al. 1991;Mallet and Carver 1995). For the morphometric measurements, empty mussel shells are scraped to remove any remaining tissues and dried for 4-5 hours (60 o C). ...
... Each characteristic should be standardized using log 10 and divided by the log 10 shell length. These morphometric variables (log-transformed and length-standardized as appropriate) should then be multiplied by their raw canonical coefficients and summed to generate a canonical variate for each individual (Mallet and Carver 1995). Mytilus edulis typically has a longer anterior adductor mussel scar, a longer hinge plate, and a greater shell height than Mytilus trossulus, resulting in positive values of the standardized canonical coefficients. ...
Mesocosms are outdoor experimental systems designed to separate and test environmental responses, in this case, cumulative effects to field-collected periphyton and macroinvertebrate communities from multiple stressors. This experimental system produces valuable, highly reproducible data, and along with field monitoring, laboratory bioassays and modeling results, provides a strong weight-of-evidence approach for aquatic risk assessment. Through the control of confounding environmental variables, this type of experiment permits the separation of interactions between multiple stressors in complex effluents or due to shifting ambient conditions. The system described is modular and was originally developed to facilitate transport of the entire system to remote or industrial test sites (e.g., for in situ 21-d chronic level testing). However, this setup is also appropriate for long term installations with suitable provision for routine maintenance and losses associated with regular wear-and-tear on equipment. The following protocol details a basic stream mesocosm system setup (e.g., 4 replicate streams per treatment-level) which is the foundation for the more than a dozen stream mesocosm experiments conducted by the authors since the 1990s.
... Les avantages démontrés sont que le milieu offshore propose des conditions d'élevage plus stables pour la mytiliculture, notamment en termes d'exposition aux stress environnementaux (e.g. stress thermique), avec des répercussions directes sur les taux de mortalité, les taux de croissance, l'état de santé des stocks à la récolte et donc sur la qualité de la production (Cheney et al., 2010;Langan, 2012;Gallardi et al., 2017;Steeves et al., 2018; (Mallet & Carver, 1995;Rayssac et al., 2010;Tremblay & Landry, 2016). (1) ponte des moules établies dans le milieu naturel au mois de juin & installation des collecteurs dans le site de captage, (2) larves en dispersion dans le milieu pélagique, (3) fixation-métamorphose des larves sur les collecteurs, (4) retrait des collecteurs en octobre-novembre, (5) boudinage du naissain récupéré, (6) installation des boudins en site de grossissement, (7) récolte partielle du stock, moules âgées de ~18 mois, (Bayne, 2004;Toupoint et al., 2012a;2012b;Gosling, 2015d ...
... Fibrous brown byssal threads extend from the closed shell and are used for attachment to substrates [103]. Shell length varies from 2 to 20 cm and total weight from 1.4 to 6.5 g [104]. Mytilus edulis is found at coastal sites of the northern Atlantic Ocean, including North America, Europe, and the northern Palearctic. ...
The use of biological objects in monitoring the state of the environment and the changes caused by the impact of environmental pollution on marine and fresh waters is a promising tool due to a lower cost in comparison to traditional monitoring and the ability to receive immediate information about the ecosystem status. In this review, we summarize the biological information about shellfish biomonitors and the results of studies focused on the development and use of the bioindicator species in early warning systems in Russia. Since the mid-1980s, Russian specialists have developed online biomonitoring systems; as in the rest of world, there are two main approaches that are currently applied to study the physiological status of potential biosensor shellfish species and to monitor freshwater and marine systems: valvometry (registration of gaping activity in bivalve mollusks) and photoplethysmography (registration of cardiac activity in mollusks and crustaceans). Valve movement responses to stressors such as abnormal conditions and pollutants include the closure of shell valves for a long period, decrease in the average distance between valves, rapid shell opening, and higher closing frequency. Cardiac activity reactions of shellfish to stress factors include rapid increases in heart rate and stress index, higher variability in heart rate than under normal conditions, and longer periods required for heart rate recovery after stress. The most common bioindicators used to monitor environmental disturbances in marine ecosystems are blue mussels, Iceland scallops, and red king crabs in cold-water habitats and Black Sea mussels in warmer waters as well as freshwater mussels and crayfish in fresh waters.
... Whilst mixed-species stocks of ME and MG are cultivated successfully along the Scottish west coast, several farm sites have experienced an increased occurrence of mussels morphologically different from native stocks, which were subsequently identified as pure MT or ME × MT hybrids, respectively (Beaumont et al., 2008). When compared with ME and MG, MT has often been associated with thin fragile shells, which easily break during harvest and processing, lowered meat yields, reduced shelf life and with more elongated shells, all of which constitute undesired traits for mussel production (Dias, Bland et al., 2009;Mallet & Carver, 1995;Penney et al., 2007). After initial reports of MT in Loch Etive, Argyll, in 2004(Beaumont et al., 2008, MT and ME × MT became the dominant species on on-growing facilities, leading to significant losses in production (only 28 tonnes were produced in 2009 compared with 240 tonnes in 2002) making mussel farming in the area economically unviable (Gubbins et al., 2012). ...
Mussels belonging to the Mytilus species complex (M. edulis, ME; M. galloprovincialis, MG; and M. trossulus, MT) often occur in sympatry, facilitating introgressive hybridisation. This may be further promoted by mussel aquaculture practices, with MT introgression often resulting in commercially unfavourable traits such as low meat yield and weak shells. To investigate the relationship between genotype and shell phenotype, genetic and morphological variability were quantified across depth (1 m to 7 m) along a cultivation rope at a mussel farm on the West coast of Scotland. A single nuclear marker (Me15/16) and a novel panel of 33 MT‐diagnostic single nucleotide polymorphisms were used to evaluate stock structure and the extent of MT introgression across depth. Variation in shell strength, determined as the maximum compression force for shell puncture, and shell shape using geometric morphometric analysis, were evaluated in relation to cultivation depth and the genetic profiles of the mussels. Overall, ME was the dominant genotype across depth, followed by ME x MG hybrids and smaller quantities of ME x MT hybrids and pure MT individuals. In parallel, we identified multiple individuals that were either predominantly homozygous or heterozygous for MT‒diagnostic alleles, likely representing pure MT and first generation ME x MT hybrids, respectively. Both the proportion of individuals carrying MT alleles and MT allele frequency declined with depth. Furthermore, MT‐introgressed individuals had significantly weaker and more elongate shells than non‐introgressed individuals. This study provides detailed insights into stock structure along a cultivation rope and suggests that practical methods to assess shell strength and shape of cultivated mussels may facilitate the rapid identification of MT, limiting the impact of this commercially damaging species.
... The blue mussel (M. edulis), is a Bivalvia of the order Mytilida, native to the North Atlantic coast but also found on the French Atlantic coast and the British Isles [6]. Dense mussel populations form beds, which are important for their survival [7]. ...
Simple Summary
Oysters and clams form an important component of the food chain and food security and are of considerable commercial value worldwide. They are affected by pollution and climate change, as well as a range of infections, some of which are opportunistic. For aquaculture purposes they are furthermore of great commercial value and changes in their immune responses can also serve as indicators of changes in ocean environments. Therefore, studies into understanding new factors in their immune systems may aid new biomarker discovery and are of considerable value. This study assessed new biomarkers relating to changes in protein function in four economically important marine molluscs, the blue mussel, soft shell clam, Eastern oyster, and Atlantic jacknife clam. These findings indicate novel regulatory mechanisms of important metabolic and immunology related pathways in these mollusks. The findings provide new understanding to how these pathways function in diverse ways in different animal species as well as aiding new biomarker discovery for Mollusca aquaculture.
Abstract
Oysters and clams are important for food security and of commercial value worldwide. They are affected by anthropogenic changes and opportunistic pathogens and can be indicators of changes in ocean environments. Therefore, studies into biomarker discovery are of considerable value. This study aimed at assessing extracellular vesicle (EV) signatures and post-translational protein deimination profiles of hemolymph from four commercially valuable Mollusca species, the blue mussel (Mytilus edulis), soft shell clam (Mya arenaria), Eastern oyster (Crassostrea virginica), and Atlantic jacknife clam (Ensis leei). EVs form part of cellular communication by transporting protein and genetic cargo and play roles in immunity and host–pathogen interactions. Protein deimination is a post-translational modification caused by peptidylarginine deiminases (PADs), and can facilitate protein moonlighting in health and disease. The current study identified hemolymph-EV profiles in the four Mollusca species, revealing some species differences. Deiminated protein candidates differed in hemolymph between the species, with some common targets between all four species (e.g., histone H3 and H4, actin, and GAPDH), while other hits were species-specific; in blue mussel these included heavy metal binding protein, heat shock proteins 60 and 90, 2-phospho-D-glycerate hydrolyase, GTP cyclohydrolase feedback regulatory protein, sodium/potassium-transporting ATPase, and fibrinogen domain containing protein. In soft shell clam specific deimination hits included dynein, MCM3-associated protein, and SCRN. In Eastern oyster specific deimination hits included muscle LIM protein, beta-1,3-glucan-binding protein, myosin heavy chain, thaumatin-like protein, vWFA domain-containing protein, BTB domain-containing protein, amylase, and beta-catenin. Deiminated proteins specific to Atlantic jackknife clam included nacre c1q domain-containing protein and PDZ domain-containing protein In addition, some proteins were common as deiminated targets between two or three of the Bivalvia species under study (e.g., EP protein, C1q domain containing protein, histone H2B, tubulin, elongation factor 1-alpha, dominin, extracellular superoxide dismutase). Protein interaction network analysis for the deiminated protein hits revealed major pathways relevant for immunity and metabolism, providing novel insights into post-translational regulation via deimination. The study contributes to EV characterization in diverse taxa and understanding of roles for PAD-mediated regulation of immune and metabolic pathways throughout phylogeny.
... In the morphometric equation, the constant b, also known as the coe⁄cient of allometry, indicates the ratio of growth rates of two variables. Morphometric analyses of marine mussels based on shell dimensions have been reported (Seed 1968(Seed , 1992Vakily, Tusycharoen & Nugranad 1988;McDonald, Seed & Koehn 1991;Karakousis & Skibinski 1992;Karakousis, Spandou, Sophronidis & Triantaphyllidis 1993;Mallet & Carver 1995;Gardner 1996). A study has been undertaken from the Indian region on the morphometric relationships in Perna viridis inhabiting Kakinada waters (Narasimham 1981). ...
The morphometry, length^weight and condition index of green mussel P. viridis (L.) from St Mary's Island, o¡ Malpe, near Udupi, were examined from December 2004 to December 2005. The calculated regression equations between length and breadth and length and width for the entire study period were L 5 0.50711 0.3921B and L 5 0.0179 1 0.3225W respectively. The monthly b values of length^breadth and length^width relationships varied from 0.3636 (March 2005) to 0.4374 (December 2004) and from 0.3022 (December 2005) to 0.3466 (August 2005) respectively. The data on length^total weight (W 5 0.0986L 2.9495), lengthŵ et tissue weight (W 5 0.031L 2.7173), length^dry weight (W 5 0.005L 2.9337) and length^shell weight (W 5 0.0351L 3.061) showed a nonlinear pattern. The coe⁄cient of allometry (b) values ranged from 2.7949 (April 2005) to 3.0999 (September 2005) for lengtht otal weight relationship and from 1.5203 (August 2005) to 3.328 (March 2005) for length^dry weight relationship. The monthly mean values of the condition index varied from 5.17 (December 2004) to 7.76 (No-vember 2005). The variation in condition index followed the breeding period and seasons. The maximum condition index (22^24) was recoded in May 2005. Based on the data on condition, it is suggested that the ideal period for commercial exploitation of Perna viridis from the Island is from March to August, when the meat yield is the highest. The hierarchical cluster analysis using complete linkage showed three major groups of biological parameters of mussels. The PCA showed a total of ¢ve components, which together accounted for 89.31% of total variance. The ¢rst component accounted for 44.08% of variance, followed by second component for 18.02% and the third component for 11.66% of variance. The remaining fourth and ¢fth components together accounted for 15.55% of variance.
... In the morphometric equation, the constant b, also known as the coe⁄cient of allometry, indicates the ratio of growth rates of two variables. Morphometric analyses of marine mussels based on shell dimensions have been reported (Seed 1968(Seed , 1992Vakily, Tusycharoen & Nugranad 1988;McDonald, Seed & Koehn 1991;Karakousis & Skibinski 1992;Karakousis, Spandou, Sophronidis & Triantaphyllidis 1993;Mallet & Carver 1995;Gardner 1996). A study has been undertaken from the Indian region on the morphometric relationships in Perna viridis inhabiting Kakinada waters (Narasimham 1981). ...
The morphometry, length^weight and condition index of green mussel P. viridis (L.) from St Mary's Island, o¡ Malpe, near Udupi, were examined from December 2004 to December 2005. The calculated regression equations between length and breadth and length and width for the entire study period were L 5 0.50711 0.3921B and L 5 0.0179 1 0.3225W respectively. The monthly b values of length^breadth and length^width relationships varied from 0.3636 (March 2005) to 0.4374 (December 2004) and from 0.3022 (December 2005) to 0.3466 (August 2005) respectively. The data on length^total weight (W 5 0.0986L 2.9495), lengthŵ et tissue weight (W 5 0.031L 2.7173), length^dry weight (W 5 0.005L 2.9337) and length^shell weight (W 5 0.0351L 3.061) showed a nonlinear pattern. The coe⁄cient of allometry (b) values ranged from 2.7949 (April 2005) to 3.0999 (September 2005) for lengtht otal weight relationship and from 1.5203 (August 2005) to 3.328 (March 2005) for length^dry weight relationship. The monthly mean values of the condition index varied from 5.17 (December 2004) to 7.76 (No-vember 2005). The variation in condition index followed the breeding period and seasons. The maximum condition index (22^24) was recoded in May 2005. Based on the data on condition, it is suggested that the ideal period for commercial exploitation of Perna viridis from the Island is from March to August, when the meat yield is the highest. The hierarchical cluster analysis using complete linkage showed three major groups of biological parameters of mussels. The PCA showed a total of ¢ve components, which together accounted for 89.31% of total variance. The ¢rst component accounted for 44.08% of variance, followed by second component for 18.02% and the third component for 11.66% of variance. The remaining fourth and ¢fth components together accounted for 15.55% of variance.
Histolo gical and statistic al studi es o n the gonad al cy cle of the musse l Lithop haga truncat a (Gray , 184 3) a long i mm ature and mat ure phase s ABSTRACT: The main purpose of this study was to investigate the gonadal cycle of the mussel Lithophaga truncata (Pelecypoda-Mytilidae) (Gray, 1843). Specimens were sampled regularly twice every season at depth 1-2 meters in the year (2015-2016) along the northern estuarine harbour of the Arabian Gulf-Saudi Arabia. Parts of gonads; ovaries and testes, were prepared for histological and statistical studies. The histological observations of the gonad indicated that there was only one gonadal cycle in the year. The ovaries produced oocytes which undergone vitellogenesis to change these oocytes into comparatively ripe ones condensed with yolk. With slide micrometre, a fixed length and width of the ovary was determined in serial histological sections (30000 µm). The different stages of the developmental oocytes were counted and statistically analysed. During November-February, the gonadal follicles appeared small and in a quiescent state. Follicles were few and scattered throughout the vesicular connective tissue. In males, the follicles were small and scattered throughout the connective tissue in the same way as females. Follicles contained undifferentiated residual cells, spermatogonia, and negligible number of primary spermatocytes. The oogonia were the most dominant type. Few of previtellogenic oocytes were observed. The ooplasm of these stages, oogonia, and previtellogenic oocytes, was homogeneous and with comparatively large nucleus. In previtellogenic oocytes, small granules of the same nature were scattered randomly in the ooplasm. These granules were consisted of proteins (peptide linkage). Carbohydrates and lipids were entirely absent. During April-July previtellogenic oocytes began to undergo growth phase and extending towards the centre of the follicles. In males, spermatogenesis became more apparent and proceeded at a faster rate. In some mussels, spermiogenesis was formed in great number. The gonadal follicles were ramified rapidly, and the development of gametes of both sexes was very fast. In females, the vitellogenic oocytes showed prominent development. The atretic oocytes and their debris were negligible. Very few number of oogonia were observed. Yolk bodies (glycoproteins) were increased rapidly and were replaced the vacuoles in the ooplasm. Other large granules gained a dark blue colour when aqueous bromophenol blue was applied. These granules were basic proteins. Other large-sized granules began to appear at the periphery of the ooplasm. These granules gained positive reaction with alcian blue, PAS and alcian blue-PAS reactions. The vitelline envelope became conspicuous under the follicle cells. Mucosubstances were positively intense at the periphery of the oocyte while proteins surrounded the nucleus. Gradually fat deposition increased. The size range of these oocytes was 130-180 µm with the ratio of the nucleus to the ooplasm 0.5: 2. During August-October both sexes had ripe gametes. In males, the central portion of the follicles was empty because of the recent discharge of large quantities of ripe gametes. At the end of this stage resorption of the gonads proceeded very rapidly and emptied follicles began to acquire an elongated form. At this stage, the oocyte attained its maximal size 180-200 µm. The mean of the total number of oocyte developmental stages in all seasons showed that the ovary was active in all seasons of the year but different labours were present. It concluded that the oogonia, the postvitellogenic oocyte development and atretic oocytes were conspicuous during the first stage of oogenesis; the vitellogenic oocytes were dominant during the second stage of oogenesis whereas the postvitellogenic and atretic oocytes were dominant during the third stage of oogenesis. All data obtained were subjected to analysis of variance (ANOVA) means significant difference P > 0.05 or P < 0.05, and Tukey post hoc test P < 0.001 and P > 0.05.
Survival of juvenile and adult blue mussels Mytilus edulis from several stocks was estimated at 3 sites in Prince Edward Island, Canada, from June 1987 to October 1988. In general, there was little evidence of spatial variability; the survival curves for a stock of a given age were similar across locations within a site and across sites. There were, however, significant differences in survival between years, stocks, and age groups. The cumulative survival was 0.77 for the period June to September 1987, as compared to 0.85 for the same period in 1988. Of the 3 groups which exhibited poor survival (0.59 to 0.72) in 1981, only one showed a similarly poor performance (0.66) in 1988. Overall, stock accounted for 28 O/O of the variation in cumulative sunrival, whereas the contribution of the other main effects was negligible. Interaction terms which included Year, Stock, and Age accounted for 42 '10 of the variance in mortality, suggesting a mutual dependence of these variables. Survival during the cold water months (October to May) was extremely high (> 0.95) for all groups.
Genetic relationships among Mytilus populations throughout the North Atlantic region, including the Mediterranean and the Baltic Sea, were studied using enzyme electrophoresis. Three distinct groups of populations, each of a remarkably wide distribution, can be recognised on the basis of their multilocus allelic composition: (1) M. galloprovincialis Lmk. of the Mediterranean and western Europe; (2) a genetically distinct form of M. edulis L. from both the Baltic Sea and some localities in the Canadian Maritime Provinces (here provisionally termed the "trossulus type mussel"); and (3) the traditional "Atlantic" M. edulis populations of northwestern European coasts and most of eastern North America.
These groups are regarded as representing three relatively old evolutionary lineages, which all deserve separate and equal systematic status. The main part of the differentiation at most of the loci studied is accounted for by this major systematic pattern, but considerable geographical differentiation within each of the three principal groups was also detected. At single loci, different electromorphs were found to prevail in disjunct populations of M. galloprovincialis (Mediterranean/Britain) and of the trossulus-type mussel (Baltic/eastern Canada). Within the Atlantic M. edulis, a major part of the differentiation is transoceanic. At one locus (Ap), geographic differentiation appeared to be relatively independent of the systematic boundaries; the possible role of interlineage hybridisation in contact areas in regulating the pattern of geographical variation is discussed.
Many authors have considered the common mussels in temperate waters of the Northern and Southern Hemispheres to be a single cosmopolitan species,Mytilus edulis Linnaeus, 1758. Others have divided these mussels into several subspecies or species. Samples of mussels were collected from 36 locations in the Northern Hemisphere and nine locations in the Southern Hemisphere. Electrophoretic evidence from eight loci indicates that the Northern Hemisphere samples consist of three electrophoretically distinguishable species:M. edulis from eastern North America and western Europe;M. galloprovincialis Lamarck, 1819 from the Mediterranean Sea, western Europe, California, and eastern Asia; andM. trossulus Gould, 1850 from the Baltic Sea, eastern Canada, western North America and the Pacific coast of Siberia. Mussels from Chile, Argentina, the Falkland Islands and the Kerguelen Islands contain alleles characteristic of all three Northern Hemisphere species, but because they are most similar toM. edulis from the Northern Hemisphere, we suggest that they tentatively be included inM. edulis. These South American samples are morphologically intermediate between Northern HemisphereM. edulis andM. trossulus. Mussels from Australia and New Zealand are similar in allele frequency and morphometric characters toM. galloprovincialis from the Northern Hemisphere. FossilMytilus sp. are present in Australia, New Zealand and South America, which suggests that the Southern Hemisphere populations may be native, rather than introduced by humans. Morphometric characters were measured on samples which the allozyme data indicated contained a single species. Canonical variates analysis of the morphometric characters yields functions which distinguish among our samples of the species in the Northern Hemisphere.
Temporal patterns of growth and survival were independently estimated for three size groups of Mytilid mussels from a commercial aquaculture farm located near Lunenburg on the Atlantic coast of Nova Scotia, Canada. The size structure of the experimental population was maintained for the duration of the study (May 1989–October 1990) by resetting each size group at intervals of ~4 months. Estimates of shell growth from late November to late February were uniformly low, less than 0.06 mm/day for all three size groups (<35 mm, 35–50 mm, > 50 mm). Beginning in early March, there was a dramatic increase in shell growth, with some of the smallest mussels exhibiting rates as high as 0.38 mm/day. From June to November, this small group showed relatively constant shell growth, whereas the two larger groups grew more slowly in the summer than in the fall, possibly due to reproductive activity. Tissue weight for these two larger groups ranged from maximum values in early May, just before spawning, to minimum values between July and October. Tissue rebuilding was evident in the fall, but was followed by a slow decline during the winter months. Temporal variations in the tissue weight of the two larger size groups were highly correlated, but showed no relationship with those of the smallest group. It would appear that the size groups were responding differently to either endogenous andJor environmental cues. Estimates of survival were lowest for all three size groups in the period from July to October, with the smallest group showing the highest losses. Correlations between shell growth and time-lagged values of tissue growth suggested that tissue synthesis generally preceded extension of the shell. Within size groups, there was a significant positive correlation between shell growth and survival; i.e. fast-growing mussels were found to have a lower risk of mortality. The annual profile of secondary production was only marginally influenced by using independent regression relationships for each of the three size groups, as opposed to using one overall relationship for each time interval. However, because size groups respond differently to endogenous and/or environmental cues, profiles of secondary production will be influenced by the size structure of the experimental population.
Inheritance of mitochondrial DNA in animals was thought to be strictly maternal. Recently, evidence for incidental paternal mtDNA leakage was obtained in hybrid crosses of Drosophila and mice. In mice, the frequency of paternal mtDNA contributions was estimated at 10(-4), compared with maternal contributions. The common occurrence in the marine mussel Mytilus of heteroplasmic individuals with two or more types of highly diverged mtDNA molecules was interpreted as strong evidence for biparental mtDNA inheritance by some, but not by others. We report here results from pair-matings involving two species of mussels, Mytilus edulis and Mytilus trossulus. Extensive contribution of paternal mtDNA, amounting to several orders of magnitude higher than that inferred for Drosophila or mice, was observed in both intra- and interspecific crosses.
Strict maternal inheritance of mitochondrial DNA is commonly observed in animals. There is usually only one mitochondrial DNA population (homoplasmy) within an individual. Mussels of the Mytilus edulis species group appear to be exceptions in both respects. Of 150 Mytilus individuals examined, 85 were heteroplasmic. Mitochondrial DNA types within heteroplasmic individuals differed greatly; in one comparison, the inferred sequence difference was 20 +/- 5 percent. Homoplasmic individuals with mitochondrial DNA similar to the heteroplasmic mitochondrial DNA types were found. These observations are best explained by the hypothesis that biparental inheritance of mitochondrial DNA can occur in Mytilus.
Cook of Corkurn's Island Mussel Farm and Mr. Peter Darnell of Indian Point Marine Farms for their cooperation and assistance in this study. We also thmk Ms. Janice Lawrence for processing the mussels for s. Teena Vincent-van de
- H Dale
H. Dale Cook of Corkurn's Island Mussel Farm
and Mr. Peter Darnell of Indian Point Marine Farms for
their cooperation and assistance in this study. We also
thmk Ms. Janice Lawrence for processing the mussels for
s. Teena Vincent-van de Riet for assist