Régime alimentaire du béluga, Delphinapterus leucas, de l'estuaire du Saint-Laurent, Canada, tel que révélé par l'analyse des acides gras du lard

Liste des illustrations

• Figure 1.1. Schéma d’un acide gras typique, avec un carbone estérifié en tête (COO^- ) et un groupe méthyle (CH₃ ) terminal. L’exemple présenté ici concerne une chaîne saturée ( i.e., pas de lien double entre les carbones) avec le 12^e carbone en position terminale (ω).
• Figure 1.2. Exemple de spécificité des voies de synthèse pour les acides gras à longue chaîne polyinsaturée. Les flèches solides indiquent les voies retrouvées chez les mammifères tandis que les flèches pointillées représentent les voies exclusives aux autres types d’organismes. Tiré de la Fig. 1 de Leonard et al. (2004) .
• Figure 1.3. Schémas typiques de l’analyse des données d’acides gras à l’aide des techniques multivarieés semblables à celles utilisées au chapitre 3 : a) démarche lors d’une analyse suivant un arbre de classification. b) démarche lors d’une analyse impliquant une suite d’analyses en composantes principales, de groupements, et des fonctions discriminantes. Les encadrés gris illustrent des exemples de sorties graphiques associées avec ces techniques de classification, soit; c) séparation en arbre de décisions, d) projections linéaires, et e) association de cas lors d’analyses de groupements.
• Figure 2.1. a) Study area (box) and b) sampling zones in the Estuary and Gulf of St. Lawrence, Canada.
• Figure 2.2. Selected species with significant amounts of the nominally ‘trace-level’ fatty acid 22:1n-7 not used in further evaluations. Dashed line = global mean of 0.27%. Diamonds are the horizontal spread across the mean (middle lines), with significant differences between species indicated by non-overlapping vertical apices.
• Figure 2.3. Cumulative mean abundance of four minor (global mean contribution <0.5%) polyunsaturated fatty acids. Species groups are ranked in descending order of abundance of the fatty acid 18:2n-6.
• Figure 2.4. Matrix scatterplot of factor scores on the retained PC Factors 1 through 4, accounting for 81.7% of total cumulative variance in the 16 logratio fatty acid variables on all samples. Groups labelled are among those that scored farthest from the central majority.
• Figure 2.5. Scatterplot of scores on Factor 1 and 2 retained from a separate PC analysis conducted on eight species of prey commonly found in the Estuary in autumn. Individual scores are indicated by species name (a) and lipid content (b).
• Figure 2.6. Original PC analysis showing only the scores for four cod species.
• Figure 2.7. Original PC analysis showing only the scores for smelt, capelin, and herring. Overlapping scores on the first two PC factors (enlarged, in upper right, with convex area shading according to species) are in contrast to separations seen in the full matrix with Factors 3 and 4 (lower left).
• Figure 2.8. Example of within-species spatiotemporal variation, with plotted scores on Factors 1 and 2 for all capelin specimens by year, season, and locations: SI = Sept-Iles (N. Gulf), NS = North Shore (Lower Estuary), SS = South Shore (Lower Estuary), UE = Upper Estuary.
• Figure 2.9. Example of between-species seasonal variability, with plotted scores on Factors 1 and 2 for autumn specimens of smelt (triangles), capelin (diamonds), herring and sardines (crosses).
• Figure 2.10. Scores on Factors 1 and 2 for autumn samples weighted by total lipid content for smelt (orange), capelin (green) and herring (blue) and herring sardines (cyan).
• Figure 2.11. Biplot on the first two discriminant functions from an analysis classifying those prey species sampled in greatest number (range = 29–126), comprising three pelagic fishes (smelt, capelin, herring), three demersal fishes (flounder, plaice, tomcod), and one invertebrate (crangon shrimp). Circles represent 95% confidence intervals of mean scores by species. Also projected are the more-important contributions from 11 of the 16 logratio fatty acids used in the classification along with individual scores.
• Figure 2.12. Biplot on the first two discriminant functions from an analysis classifying 15 species groups (>17 samples each, total n = 699) of potential prey of beluga, using 16 fatty acid logratios as input variables. Circles denote 95% confidence intervals for mean scores by group (sculpins and shrimps comprised three species each). Non-overlapping circles indicate significantly different groups. Oblique labels suggest species associations. For reference, scores are plotted for all samples, including those not used in the analysis, such as eels and whelks (shaded areas). Selected individuals of Greenland halibut are marked as being distinct from their species group. Variables are projected according to their relative contributions on the two discriminant functions. For clarity, the minor contributions of fatty acids 18:3n-3, 20:1n-11, and 22:1n-9 are not included.
• Figure 3.1. Approximate sampling locations in the Estuary and Gulf of St. Lawrence. Beluga carcasses were recovered along the shores of the lower Estuary (dashed outline). Seals were from (1) Bic, for harbour and grey seals (Estuary), (2) Godbout, for harp seals (Estuary), (3) near the Magadalen Islands for breeding harp seals (Gulf), (4) adjacent to Prince Edward Island (P.E.I.) for breeding hooded seals (Gulf), and (5) near Port Hood, Nova Scotia for breeding grey seals (Gulf).
• Figure 3.2. Classification trees for five different species of marine mammals ( n = 143) collected in the Estuary and Gulf of St. Lawrence grouped by species: (a) initial classification using all available (56) fatty acids, (b) classification produced while using the reduced set of 18 fatty acids. Fatty acids in rounded boxes represent variables and the level (% amount) chosen to split cases. The number of individuals of each species are listed in the terminal nodes (squared boxes), with the numerically dominant species in bold and the ‘misclassified’ individuals in normal type. Species classes are beluga (Dl), harbour seals (Pv), harp seals (Pg), grey seals (Hg), and hooded seals (Cc). Total misclassification rate was 10 and 11 of 143 individuals for (a) and (b) respectively.
• Figure 3.3. Classification trees by gender for adult male (M) and female (F) beluga (a), hooded seals (b), harp seals (c), grey seals (d) and harbour seals (e and f) as determined by CART while using the set of 18 fatty acids.
• Figure 3.4. Classification trees by age-class (P = neonates; J = sub-adults; A = adults) for (a) harp seals, (b) grey seals, and (c) harbour seals, as determined by CART while using the set of 18 fatty acids.
• Figure 3.5. Varimax-rotated PC factor scores of the five marine mammal species on a matrix of of 4 PCs obtained using 17 fatty acid logratio variables, with species groups as marked. A separate label was added for a newborn beluga (black cross) and three beluga males (blue halos) that scored away from other belugas and towards the pinnipeds on PC 1.
• Figure 3.6. Discriminant functions analysis of the five species of marine mammals using (a) scores on the four factors retained from the principal components (PC) analysis, and (b) the 17 fatty acid logratios as input variables. Group centroids (star) and 95% confidence intervals are indicated for each species. Variables (PCs or fatty acids) are projected (rescaled to 200% for visibility) according to their relative contributions on the two discriminant functions. The cross-validated classification success rate was 84% and 99% (120/143 and 142/143 individuals correctly classified) for (a) and (b), respectively.
• Figure 3.7. Dendrogram of hierarchical clustering with Ward’s method using the four principal component factors as input variables. Horizontal scale denotes the increase in within-cluster’s variance, rescaled from 0 to 25. Vertical dashed line highlights the joining of cases into a nine-cluster solution. Individual members are summarised in each cluster by their species: hooded seals (Cc), beluga (Dl), grey seals (Hg), harp seals (Pg), and harbour seals (Pv). Hooded seals comprised only adult individuals. Belugas were all adults except for one individual each in clusters 2 and 4. Beluga and hooded seals are sub-labelled by gender: female (F), and male (M). Other pinnipeds are sub-labelled by age-class: adult (A), sub-adults (J), and neonates or pups (P). The highest aggregation into two clusters is suggested by the labelled boxes for a grouping of belugas and principally sub-adults seals from the Estuary relative to all other pinnipeds from the Estuary and the Gulf.
• Figure 3.8. Mean diamond scatterplots of scores for all individuals by cluster number on PC factors 1 through 4 (a-d). Diamonds indicate cluster group means ± 95% confidence intervals (vertically) in proportion to group size (horizontally). Scores are marked by species: beluga (open circles), hooded seals (triangles), harbour seals (open boxes), grey seals (x), and harp seals (crosses).
• Figure 3.9. Discriminant function analysis of the classification results for the nine clusters using (a) the four principal components (PC) or (b) the set of 17 fatty acid logratios as input variables. Large circles denote the 95% confidence interval centroids of mean scores (stars) for clusters 1 through 9. Variables are projected (rescaled to 200% for visibility) according to their relative contributions on the two discriminant functions. The overall classification success rate was (a) 97% (139/143 individuals correctly classified) and (b) 93% (133/143 correct assignments).
• Figure III a). Cumulative mean abundance for 25 fatty acids as ranked by species.
• Figure III b). Scatterplot of all scores on PC Factors 1 and 3 when weighted by total lipid content. Labels indicate examples of three distinctive groups (scoring apart from majority) that also had high lipid content.
• Figure III c) Full matrix for PC 1 through 4, showing individual scores of capelin only. Subregions were for SI = Sept-Iles, NS = North Shore and SS = South Shore of Lower Estuary, respectively, and UE = Upper Estuary. Seasons were spring (April-June), summer (July-August), and autumn (Sept.-Nov.).
• Figure III d) Biplot of first two Discriminant Functions classifying specimens of common species from the spring of 2001 into two groups: PELAGIC (smelt, capelin, herring, and turbot) with green markers, and DEMERSAL (tomcod, flounder, and crangon shrimp) with red markers. Circles indicate 95% confidence intervals for group means. Shading indicates notable misclassified specimens (tomcod = Y and flounder = open squares).
• Figure III e) Biplot of the first two discriminant functions classifying autumn samples (2000-2001) into four composite species groups when using the set of 16 fatty acid variables. The groupings were for flatfishes (flounder and plaice: open squares), marine shrimps (eualids and pandalids: +), pelagic fishes (smelt, herring, and capelin: small squares) and crangons (estuarine sand shrimp: z). Shading indicates the spread of samples from the group mean scores in the darker circles (= 95% confidence intervals). Also plotted were those species sampled in lesser abundance and not used to calculate the functions (greyed-out symbols). 12 of the 16 logratio fatty acid variables used as input variables are labelled with their relative projected contributions.
• Figure IV a) Alternate view of Fig. 3.5a, with outlines for three males and one newborn beluga (1), and harbour seal neonates (2).
• Figure IV b) Alternate view of Fig. 3.6b, for a “traditional’ presentation as seen in most publications. All individual scores are plotted on the first 2 DFs (canonical variates), without projections of fatty acid variables.
• Figure IV c) Second alternate view of Fig. 3.6b, with outlined boxes to suggest nested ‘metapatterns’ of groupings discriminating belugas (1) vs. seals (2), then hooded vs. other seals (3) along the first DF, then harbour seals vs. greys and harps along the second DF (4).
• Figure IV d) Third alternate view of Fig. 3.6b when using three DFs, or canonical variates. The third DF (Canon[3]) enhanced discrimination of hooded seals and grey seals, and to a lesser extent, harp seals or harbour seals. Belugas and hooded seals are represented here by the larger cubes relative to the other species.