How geographic distance and depth drive ecological variability and isolation of demersal fish communities in an archipelago system (Cape Verde, Eastern Atlantic Ocean)

Cape Verde is a tropical oceanic ecosystem, highly fragmented and dispersed, with islands physically isolated by distance and depth. To understand how isolation affects the ecological variability in this archipelago, we conducted a research project on the community structure of the 18 commercially most important demersal fishes. An index of ecological distance based on species relative dominance (Di) is developed from Catch Per Unit Effort, derived from an extensive database of artisanal fisheries. Two ecological measures of distance between islands are calculated: at the species level, DDi, and at the community level, DD (sum of DDi). A physical isolation factor (Idb) combining distance (d) and bathymetry (b) is proposed. Covariance analysis shows that isolation factor is positively correlated with both DDi and DD, suggesting that Idb can be considered as an ecological isolation factor. The effect of Idb varies with season and species. This effect is stronger in summer (May to November), than in winter (December to April), which appears to be more unstable. Species react differently to Idb, independently of season. A principal component analysis on the monthly (DDi) for the 12 islands and the 18 species, complemented by an agglomerative hierarchical clustering, shows a geographic pattern of island organization, according to Idb. Results indicate that the ecological structure of demersal fish communities of Cape Verde archipelago, both in time and space, can be explained by a geographic isolation factor. The analytical approach used here is promising and could be tested in other archipelago systems

Connectivité entre les populations du fjord du Saguenay et celles du golfe du Saint-Laurent

L’analyse des marqueurs microsatellites et d’allozymes chez différentes espèces de poissons de fond (morue, flétan du Groenland et sébaste) et de crustacés (crabe des neiges et crevette nordique) montre que les organismes du Saguenay et du Saint-Laurent appartiennent aux mêmes populations. La seule différenciation génétique est observée au locus Pan I chez la morue. Cette différenciation pourrait toutefois être causée par la sélection, qui agirait dans le fjord du Saguenay, plutôt que par l’isolement génétique de la population. Les données complémentaires disponibles pour les poissons de fond (composition élémentaire des otolithes, morphométrie et faune parasitaire) montrent que les individus capturés dans le Saguenay diffèrent de ceux du Saint-Laurent. Ces différences suggèrent que les individus du Saguenay et du Saint-Laurent passent la majeure partie de leur cycle vital dans des environnements différents. Considérant la très faible survie larvaire observée dans le fjord, cette revue suggère que les populations de poissons de fond du Saguenay constituent des populations puits, dont le recrutement dépend de l’apport de juvéniles depuis le Saint-Laurent. Une fois les individus installés dans le Saguenay, ils y passent la majorité de leur vie. Même si nous ne possédons pas de données complémentaires pour les crustacés, il est possible que le même mécanisme opère chez ces espèces.Microsatellite and allozyme analyses on various species of bottom fishes (cod, Greenland halibut and redfish) and crustaceans (snow crab, northern shrimp) show that individuals from the Saguenay Fjord and from the St. Lawrence belong to the same populations. The only genetic difference observed is at the Pan I locus of cod. This differentiation may be caused by selection that would act in the Saguenay Fjord, rather than due to the genetic isolation of the population. Complementary data available for bottom fish (elemental composition of otoliths, body morphometry, and parasite fauna) show clear differences between the Saguenay and the St. Lawrence. These differences suggest residence of individuals in the Saguenay and the St. Lawrence for a large proportion of their life cycle. Considering the low larval survival observed in the fjord, this review suggests that the bottom fish populations from the Saguenay represent sink populations whose recruitment depends largely or solely on migration of juveniles from the St. Lawrence. Although there are no complementary data for crustacean species, it is possible that migration and residence are processes operating for those species as well

Tracking larvae with molecular markers reveals high relatedness and early seasonal recruitment success in a partially spawning marine bivalve

The partial synchronized spawning strategy\ud adopted by some marine invertebrate broadcast-spawners\ud can lead to the production of many distinct pools of larvae\ud within a single reproductive cycle. Following the fate of\ud these larval groups from birth to settlement with molecular\ud markers might shed light on mechanisms regulating their\ud population recruitment. Larvae and recruits of Mya arenaria,\ud a partially spawning marine bivalve, were monitored\ud and collected over 13 consecutive weeks during an entire\ud reproductive cycle. Each sampled individual (n = 218)\ud was sorted according to size (early veligers, late veligers,\ud post-larval recruits) and genotyped at seven microsatellite\ud loci for comparisons among samples and with adult reference\ud samples (n = 270). While traditional differentiation\ud statistics (e.g., pairwise ϴST, allelic richness) suggested\ud the absence of sweepstakes reproductive success, the level of relatedness found within and among larvae and recruit\ud samples suggested otherwise. Four samples out of ten were\ud observed to have higher within-sample relatedness values\ud than randomly expected, including the very first group\ud of early veligers produced in the season (E1) and the last\ud group of post-larvae who survived recruitment (P10). E1\ud individuals were also found to be more related than randomly\ud expected to individuals of more than 80 % of all\ud other samples including the last surviving recruits (P8 and\ud P10). These results suggest that the first larvae produced\ud in the season were the most successful to survive recruitment.\ud Results also show direct evidence for larval retention\ud and demonstrate for the first time larval and post-larval kin\ud aggregation in a marine bivalve

Expression of genes involved in key metabolic processes during winter flounder (Pseudopleuronectes americanus) metamorphosis

L’étude avait pour but d’établir une meilleure compréhension des évènements moléculaires qui régissent l’ontogénèse chez la plie rouge (Pseudopleuronectes americanus (Walbaum, 1792)). L’expression de sept gènes intervenant dans des processus métaboliques clés durant la métamorphose a été mesurée au moment de la déposition (S0) et après 15 (S15) et 30 (S30) jours suivant cette dernière, et comparée à celle de larves pélagiques avant la déposition (PL). Deux stades critiques ont été cernés : (1) la transition des larves de l’habitat pélagique à l’habitat benthique (de PL à S0) et (2) la maturation de métamorphose, durant laquelle la larve demeure déposée sans croître (de S0 à S30). L’expression génique de l’hormone de croissance (gh) a augmenté de manière significative à S0. À S30, une augmentation de l’expression génique de la cytochrome oxydase (cox) a eu lieu, de concert avec une deuxième augmentation de l’expression génique de la gh, ce qui laisse croire qu’une capacité aérobie accrue supportait la croissance avant la baisse de température automnale. Les patrons d’expression des gènes de la pyruvate kinase (pk), de la glucose-6-phosphate déshydrogénase (g6pd) et de la lipase stimulée par les sels biliaires (bal) indiquaient que la synthèse énergétique pourrait être principalement assurée par la glycolyse au stade PL, par la voie pentose–phosphate à la déposition et par le métabolisme des lipides à S30. L’expression des gènes de la protéine de choc thermique 70 (hsp70), de la superoxyde dismutase (sod), de la cox et de la peroxyrédoxine-6 (prx6) a révélé que le stress oxydatif et le développement d’une protection anti-oxydation en découlant étaient limités durant le stade PL, renforcés à la déposition et très élevés à S30, sans doute en raison du taux de croissance accru observé à cette période. -- Mots-clés : métamorphose ; hormone de croissance ; enzymes antioxydantes ; métabolisme énergétique ; plie rouge ; Pseudopleuronectes americanus

Effects of algae-enriched rotifers on winter flounder (Pseudopleuronectes americanus) gene expression during metamorphosis

International audienceThe aim of this study was to evaluate the effect of a dietary highly unsaturated fatty acid (HUFA) deficiency on winter flounder Pseudopleuronectes americanus metamorphosis by examining the growth and the expression of genes involved in some key metabolic processes: lipid digestion, oxidative stress, and growth. Three groups of fish were fed rotifers enriched with different blends of microalgae providing different HUFA profiles: (1) a diet comprising a mixture of three microalgae, Nannochloropsis oculata, Isochrysis galbana, and Pavlova lutheri (Cocktail diet), which contained a balanced combination of ecosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and arachidonic acid (AA); (2) the N. oculata diet (nanno diet), with a low level of DHA; and (3) the I. galbana diet (Tiso diet), characterized by low levels of EPA and AA. The results indicate that the need for DHA increased from settlement and for EPA and aa from 15 days after settlement. The lower HUFA content in the Tiso and nanno diets did not affect larval development or lipid reserve accumulation. The superoxide dismutase gene expression suggests a reduced oxidative stress in the Cocktail group, and overall results indicate that gh gene expression could be a valuable indicator of development at the molecular level in response to dietary HUFA quality during metamorphosis in winter flounder

Physiological and biochemical indicators of mussel seed quality in relation to temperatures

The bivalve’s aquaculture industry is an important component of the economy in Eastern Canada. Seed collection is an initial and critical activity in most bivalve aquaculture industries including mussel farming in Prince Edward Island, production is entirely dependent on natural spat collection. Although seed supply is not a concern from a quantitative standpoint, there are growing concerns about the quality of natural seed. The general objective of this study was to identify and assess mussel seed quality criteria on the basis of physiological and biochemical status under laboratory and field conditions. The performance, as estimated by metabolic measurements, lipid class composition, multi-locus heterozygosity (MLH) and survival to stressful environment of seed from 6 different stocks sources was first compared under laboratory conditions at 12 °C and 25 °C. Results showed that MLH varied among the six sources of mussels in a way which is consistent with the physiological and biochemical indicators of seed quality. Mussels from Shippagan (New Brunswick) and Tracadie (Prince Edward Island) were found to have the highest quality scores and the best adaptive capacity to extreme water temperature under laboratory conditions. The results of the stock-site reciprocal field studies are in general agreement with those of the laboratory experiments with higher survival of mussels from Shippagan, Tracadie and St. Peters Bays in the various study sites. Our results suggest that the measure of MLH and survival curves at stressful temperature could be a good criteria combination to identify the improved survival potential of mussels stocks

Biochemical and genetic characteristics of suspension-cultured mussels ( Mytilus edulis ) in relation to byssal thread production and losses by fall-off

International audienceMussel culture relies on the mussel self-attachment capacity through byssus production. By doing so, no cages or containment devices are needed. It has been previously suggested that thread production requires a non-negligible part of the energy expenditure in blue mussels Mytilus edulis. Therefore our work investigates the relationships between byssal thread production, mussels energetic reserves and phospholipids profiles in the foot. The relationship between thread production and heterozygosity was also examined. The study was realized in a small lagoon of the Îles-de-la-Madeleine, southern Gulf of St. Lawrence, Canada, on four sampling dates between June and September encompassing the pre- to post-spawning periods. Our results show a significant relationship between the thread numbers and attachment strength. However, no correlations were found between energy reserves, phospholipids composition of the foot or heterozygosity level and byssal production. Our results suggest that mussels in suspension culture in this lagoon were not energy-limited so that the energy reserves did not influence the byssal thread production