Les spatangoïdes (échinides détritivores fouisseurs) possèdent un volumineux caecum qui s’ouvre au début de l’estomac, le caecum gastrique. Ce caecum est ‘distendu’ :il est toujours gorgé d’un liquide incolore dont la nature est inconnue. Les sédiments ingérés par ces oursins et qui occupent le reste du tube digestif, ne pénètrent jamais dans le caecum. La fonction du caecum gastrique n’est pas claire: il sécréterait des enzymes dans l’estomac, serait un site d’absorption, ou encore abriterait une microflore cellulolytique. En prenant pour modèle l’un des échinides fouisseurs les plus étudiés, Echinocardium cordatum, ce travail tente d’élucider le rôle du caecum gastrique, et s’intéresse plus particulièrement à l’étude de son contenu.<p>Les résultats indiquent que le caecum gastrique d’E. cordatum contient de l’eau de mer. L’entrée d’eau de mer dans le caecum a été visualisée en la colorant et des caractéristiques communes au liquide caecal et à l’eau de mer environnante ont été observées: une même osmolarité, les mêmes particules détritiques en suspension et les mêmes communautés bactériennes. Le caecum gastrique contient de la matière organique en suspension (détritus, bactéries transitoires); il est également absorbant. Ses capacités d’absorption ont été comparées à celles de l’estomac et de l’intestin grâce à un dispositif expérimental particulier :les chambres de Ussing. Les résultats ont montré que les entérocytes du caecum et de l’intestin participent davantage au transfert de glucose vers la cavité coelomique que ceux de l’estomac.<p>Un schéma de la circulation de l’eau de mer dans le tube digestif est proposé. L’eau de mer qui circule à la surface du corps de l’oursin et qui provient de la surface des sédiments atteint la cavité buccale, une circulation entretenue par la ciliature des clavules (piquants ciliés). Le péristaltisme de l’œsophage et celui du siphon assurent l’entrée d’eau de mer dans le tube digestif. Une partie de cette eau entre dans le siphon qui l’amène dans l’intestin d’où elle est entraînée à l’extérieur avec le bol alimentaire. L’eau de mer qui n’est pas prélevée par le siphon peut atteindre l’entrée du caecum gastrique. Un système de gouttières a été mis en évidence à l’entrée du caecum. Il s’étend de l’estomac au début du caecum où les gouttières sont flagellées, et acheminerait l’eau de mer dans la lumière caecale. Les différences de pression osmotique entre le liquide caecal et le liquide cœlomique permettraient le transfert d’eau depuis le caecum vers la cavité cœlomique. Une quantité d’eau similaire devrait alors être éliminée de la cavité coelomique. Cette élimination semble se faire dans le caecum intestinal, l’eau serait ensuite éliminée par l’anus. <p>D’après nos observations, le caecum gastrique pourrait être le site d’une digestion et d’une absorption de la matière organique détritique de l’eau de mer. Si cette hypothèse est exacte, E. cordatum serait alors un détritivore particulièrement ‘complet’, digérant non seulement la fraction détritique des sédiments mais aussi celle en suspension dans l’eau de mer. Ce modèle pourrait correspondre à tous les échinides atélostomes (spatangoïdes & holastéroïdes) qui, outre la présence d’un caecum gastrique bien développé et rempli de liquide, ont en commun d’être fouisseurs, et d’entretenir une circulation d’eau dans leur terrier grâce à des clavules groupés en fascioles.<p><p>Spatangoids (burrowed deposit-feeding echinoids) have a large caecum, which opens at the beginning of the stomach, the gastric caecum. It is always swollen, filled with a colorless liquid whose nature is unknown; sediments ingested by sea urchins fill the rest of the digestive tract but never enter in the caecum. The function of the gastric caecum is unclear: it would secrete enzymes in the stomach, would be a site of absorption, and/or would harbor a cellulolytic microflora. By taking as model one of the most studied burrowing echinoids, Echinocardium cordatum, this study attempts to highlight the role of the gastric caecum by examining its contents.<p>Results indicate that the gastric caecum of E. cordatum contains seawater. Seawater inflow into the caecum was visualized using dye. The caecal liquid and the surrounding seawater were demonstrated to have similar characteristics: the same osmolarity, the same suspended particles and the same bacterial communities. The gastric caecum contains suspended organic matter (detritus, transient bacteria) and is also involved in absorption. Absorption and transfer of glucose were compared between the gastric caecum, the stomach and the intestine, using a particular experimental device: the Ussing chamber. The results showed that the enterocytes of the caecum and of the intestine were more involved in glucose transfer to the coelomic cavity than those of the stomach.<p>Seawater circulation in the digestive tube is tentatively described. Seawater currents along the body of the sea urchin originate from the sediment surface and reach the mouth; this circulation is generated by ciliae of specialized spines, the clavules. Peristalsis of the esophagus and of the siphon induces seawater to enter the mouth and to move along the digestive tube. Part of this water enters the siphon, being then transported to the intestine, and driven outside via the anus. Seawater that has not been taken by the siphon can reach the opening of the gastric caecum. A system of grooves occurring at the entrance of the caecum extends from the anterior stomach to the proximal part of the caecum where it is flagellated; these grooves could transport seawater in the caecal lumen. Differences in osmotic pressures between the caecal liquid and the coelomic liquid could transfer water from the caecum to the coelomic cavity. A similar uptake of water could then be removed from the coelom through the wall of the intestinal caecum, and water be eliminated from the digestive tube via the anus.<p>According to our observations, the gastric caecum could be specialized in digestion and absorption of detrital organic matter occurring in seawater. If this hypothesis is correct, E. cordatum would be a deposit-feeder feeding both on the detritus fraction of the sediments and on that of seawater. This model could fit all Atelostomata echinoids (spatangoids & holasteroids) which, besides the presence of a well-developed gastric caecum filled with liquid, have in common the burrowing behaviour, and the maintenance of seawater currents in their burrows owing to the action of clavules grouped into fascioles.<p><p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

<p>Sea urchins are fascinating marine creatures belonging to the phylum Echinodermata that serve as an essential ecological component and hold promise as a prospective source of therapeutics. However, sudden environmental changes, such as global warming and marine pollution, are placing significant stress on these organisms. To maintain natural resources and exploit sea urchins commercially, researchers are investigating aquaculture as a solution.</p> <p>This investigation discloses the physiological and immunological effects of physical and chemical stressors on one of the most common edible species of sea urchin, <em>Arbacia punctulata</em>. The study employed an elevated temperature as a physical stressor (1°C/day), lipopolysaccharides (LPS) inoculation as a chemical stressor (4µg/ml/day), and a combination of both LPS and elevated temperature as combined stressors. The results demonstrated a significant alteration in the total and differential coelomocyte count in the LPS-stressed group (p<0.05) and combined stressed group (p<0.05) followed by abnormal behavioral activity compared to those of control. Additionally, exposure to acute LPS exposure (at day 1 and day 3) and combined stressors led to an increase in phagocytic capacity (p<0.05) and lysozyme activity (p<0.05). Chronic exposure to LPS and combined stressors resulted in a decrease in gonadosomatic index (p<0.05, at day 10) and lysozyme activity (at day 7). A significant increase in coelomic fluid (CF) protein (p<0.05)was observed in the temperature-stressed group on days 5 and 10, while the combined stressed group had significantly more CF protein on days 1, 5, 7, and 10. An upregulation of Nf-kB gene expression was also observed (p>0.05) in temperature stressed group.  </p> <p>The study also revealed that sea urchins contain bioactive compounds that protect against external and internal injury, cell death, and body wall extract of sea urchin exhibited high antioxidant activity(p<0.05). Furthermore, it confirmed the antibacterial activity (p<0.05) of sea urchin (<em>Arbacia punctulata </em>and<em> Lytechinus variegatus</em>) body wall and coelomic fluid (cell-free plasma) extracts against ten pathogenic bacteria. The ethyl acetate body wall extract of both sea urchin species demonstrated higher inhibitory activity against the pathogenic bacteria tested. Overall sea urchin has potentials to meet the demand of food and medicine. </p>

Anthropogenic carbon dioxide (CO2) emissions are increasing the atmospheric CO2 concentration and the oceans are absorbing around 1/3 them. The CO2 hydrolysis increases the H+ concentration, decreasing the pH, while the proportions of the HCO3- and CO32- ions are also affected. This process already led to a decrease of 0.1 pH units in surface seawater. According to "business-as-usual" models, provided by the Intergovernmental Panel on Climate Change (IPCC), the pH is expected to decrease 0.3-0.5 units by 2100 and 0.7-0.8 by 2300. As a result the surface ocean carbonates chemistry will also change: with increasing pCO2, dissolved inorganic carbon will increase and the equilibrium of the carbonate system will shift to higher CO2 and HCO3– levels, while CO32– concentration will decrease. Surface seawaters will progressively become less saturated towards calcite and aragonite saturation state and some particular polar and cold water regions could even become completely undersaturated within the next 50 years. <p>Responses of marine organisms to environmental hypercapnia, i.e. to an excess of CO2 in the aquatic environment, can be extremely variable and the degree of sensitivity varies between species and life stages. Sea urchins are key stone species in many marine ecosystems. They are considered to be particularly vulnerable to ocean acidification effects not only due to the nature of their skeleton (magnesium calcite) whose solubility is similar or higher than that of aragonite, but also because they lack an efficient ion regulatory machinery, being therefore considered poor acid-base regulators. Populations from polar regions are expected to be at an even higher risk since the carbonate chemical changes in surface ocean waters are happening there at a faster rate. <p>The goal of this work was to study the effects of low seawater pH exposure of different life stages of sea urchins, in order to better understand how species from different environments and/or geographic origins would respond and if there would be scope for possible adaptation and/or acclimatization.<p>In a first stage we investigated the effects of ocean acidification on the early stages of an intertidal species from temperate regions, the Atlantic Paracentrotus lividus sea urchin, and of a sub-Antarctic species, Arbacia dufresnei. The fertilization, larval development and larval growth were studied on specimens submitted through different pH experimental treatments. The fertilization rate of P. lividus gametes whose progenitors came from a tide pool with high pH decrease was significantly higher, indicating a possible acclimatization or adaptation of gametes to pH stress. Larval size in both species decreased significantly in low pH treatments. However, smaller A. dufresnei echinoplutei were isometric to those of control treatments, showing that size reduction was most likely due to a slower growth rate. In the pH 7.4 (predicted for 2300) treatment, P. lividus presented significantly more abnormal forms than control ones, but A. dufresnei did not. The latter does not seem to be more vulnerable than temperate species, most likely due to acclimatization/adaptation to lower pH seasonal fluctuations experienced by individuals of this population during spring time.<p>In a second stage, adult physiological responses of P. lividus and A. dufresnei to low pH seawaters were studied. Intertidal field P. lividus specimens can experience pH fluctuations of 0.4 units during low tidal cycles, but their coelomic fluid pH will not change. During experimental exposure to low pH, the coelomic fluid (extracellular) pH of both species decreased after weeks of exposure to low seawater pH. However, it owned a certain buffer capacity (higher than that of seawater) which did not seem to be related to passive skeleton dissolution. In laboratory studies, the feeding rate of P. lividus, the RNA/DNA ratio (proxy for protein synthesis and thus metabolism) of both the gonads and the body wall of the studied species and the carbonic anhydrase activity in the body wall (an enzyme involved in calcification and respiratory processes) of A. dufresnei did not differ according to seawater pH. The same was true for spine regeneration (a proxy for calcification) of both species. This shows that both P. lividus and A. dufresnei are able to cope when exposed to mild hypercapnia (lowest investigated pH 7.4) for a mid-term period of time (weeks). In a different set of experiments, pH effects were tested on P. lividus individuals together with two temperatures (10ºC and 16ºC). The pH decrease of the coelomic fluid did not vary between temperatures, neither did its buffer response. The oxygen uptake rates of P. lividus (as a proxy for global metabolic state of the whole organism) increased in lower pH treatments (7.7 and 7.4) in organisms exposed to lower temperatures (10ºC), showing that this was upregulated and that organisms experienced a higher energetic demand to maintain normal physiological functions. For instance, gonad production (given by the RNA/DNA ratio) was not affected neither by temperature, nor pH.<p>Finally, possible morphological and chemical adaptations of cidaroid (“naked”) spines, which are not covered by epidermis, to low magnesium calcite saturation states were investigated. Deep sea field specimens from the Weddell Sea (Antarctica), Ctenocidaris speciosa were studied. Cidaroid spines have an exterior skeleton layer with a polycrystalline constitution that apparently protects the interior part of the monocrystaline skeleton, the stereom (tridimensional magnesium calcite lattice). The cortex of C. speciosa was by its turn divided into two layers. From these, it presented a thicker inner cortex layer and a lower Mg content in specimens collected below the aragonite saturation horizon. The naked cortex seems able to resist to low calcium carbonate saturation state. We suggest that this could be linked to the important organic matrix that surrounds the crystallites of the cortex.<p>Some echinoid species present adaptive features that enable them to deal with low pH stresses. This seems to be related to the environmental conditions to which populations are submitted to. Therefore, organisms already submitted to pH daily or seasonal fluctuations or living in environments undersaturated in calcium carbonate seem to be able to cope with environmental conditions expected in an acidified ocean. Under the realistic scenario of a decrease of ca. 0.4 units of pH by 2100, sea urchins, and echinoderms in general, appear to be robust for most studied processes. Even thought, this general response can depend on different parameters such as exposure time, pH level tested, the process and the life stage considered, our results show that there is scope for echinoids to cope with ocean acidification.<p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Ce travail s’est intéressé aux liens existant entre la stratégie d’exploitation développée par un crustacé ectoparasite et son comportement reproductif. Le crabe Pinnotheridae Dissodactylus<p>primitivus exploite deux espèces Spatangidae vivant dans la Mer des Caraïbes, Meoma<p>ventricosa et Plagiobrissus grandis. Des approches comportementales, démographiques et<p>génétiques ont été adoptées afin de mettre en lumière le fonctionnement et la biologie de cette<p>symbiose. Par son comportement alimentaire, le crabe occasionne des lésions tégumentaires<p>sur ses hôtes. Celles-ci affectent la fitness de M. ventricosa, au travers de son développement<p>gonadique. Dissodactylus primitivus exploite ses deux espèces hôtes de façon asymétrique. La<p>reproduction des parasites se déroule sur les deux hôtes, alors que le recrutement ne s’effectue<p>que sur M. ventricosa. Ce cycle vital asymétrique du crabe serait stabilisé par la qualité et la<p>rareté de P. grandis. En outre, Le comportement sexuel du crabe sur M. ventricosa répondrait<p>aux critères de la polygynandrie à femelles mobiles. Selon ce modèle, les mâles et les<p>femelles se déplacent entre les hôtes à la recherche de partenaires multiples. Lors de ces<p>déplacements, le crabe s’aiderait de son aptitude à localiser chimiquement ses hôtes.<p>Néanmoins, ce mécanisme s’avère plastique et pourrait refléter l’asymétrie du cycle vital. En<p>effet, cette différence n’a pas d’origine génétique, car les crabes vivant au sein du site d’étude constituent la même population quelle que soit l’espèce hôte considérée. Les marqueurs<p>moléculaires microsatellites mis au point dans ce travail permettront lors de futurs travaux<p>d’affiner les observations sur les modalités d’accouplement du crabe et d’estimer sa capacité<p>de dispersion.<p><p>This work aimed to highlight the relationships between the host exploitation strategy of an<p>ectoparasite crustacean and its mating system. The pea crab Dissodactylus primitivus exploits<p>two Spatangidae species living in the Caribbean Sea, Meoma ventricosa and Plagiobrissus<p>grandis. Behavioural, demographic and genetic approaches have been conducted to examine<p>the functioning and biology of this symbiosis. Owing to its feeding behaviour, the crab<p>wounds the host tegument. The wounds negatively affect M. ventricosa's fitness through its<p>gonadic development. Dissodactylus primitivus asymmetrically exploits its two host species.<p>The reproduction of the parasites happens on each host, but the recruitment only takes place<p>on M. ventricosa. The asymmetrical life cycle would be stabilised par the quality and the<p>scarcity of P. grandis. The mating system of crabs living on M. ventricosa would correspond<p>to the Pure-search polygynandry of mobile females criteria. According to this model, the<p>males and the females practice the host switching behaviour to find several sexual partners.<p>During these movements, the crab could use its chemodetection ability to locate its hosts.<p>However, this mechanism is plastic and presumably reflects the asymmetrical life cycle of the<p>crab. This difference has indeed not a genetic cause because the crabs living inside the<p>investigated region belong to the same population, whatever the regarded host species. In<p>future studies, the microsatellites markers developed for this work could be used to test the<p>mating system of D. primitivus and to estimate its dispersion ability. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

What makes a community sustainable? Is it the effective management of local environmental resources? Or meeting the social, economic and health needs of its population? For the five UBC researchers in the following pages, the answer is unequivocally both. From tackling water scarcity to environmental health and planning, these researchers are individually working to ensure local communities are equipped with the necessary knowledge to remain sustainable for generations to come.

Comparer les structures génétiques des populations d’un couple hôte-parasite permet d’évaluer les facteurs qui façonnent la dispersion ainsi que la potentialité d’adaptation locale de ces espèces. Le modèle étudié est le crabe ectoparasite Dissodactylus primitivus et son oursin-hôte Meoma ventricosa, endémiques des Caraïbes et des côtes américaines voisines. <p>En étudiant des populations le long de l’arc antillais et de la côte panaméenne, ce travail a mis en évidence que la structure génétique des populations du parasite D. primitivus diffère fortement de celle de son hôte M. ventricosa (microsatellites et cytochrome oxydase I). En effet, alors que les populations du parasite présentent une différenciation au sein de cette région, celles de l’hôte sont génétiquement homogènes. Ce contraste peut être expliqué par des caractères biologiques et écologiques (fécondité, habilité à la nage, disponibilité de l’habitat) et suggère des potentialités d’adaptation locale distinctes. La distance géographique semble être importante dans la structuration des populations du crabe mais la courantologie ou encore des évènements passés (glaciations) jouent également un rôle. A l’échelle d’une même île, les crabes ne présentent pas de différenciation entre des sites distincts. En outre, nous avons pu montrer que des crabes issus d’hôtes d’espèces différentes ne sont pas différenciés génétiquement ce qui pourrait être liée à la mobilité des crabes adultes. Par des analyses de paternité, nous avons souligné cette mobilité, démontrant que le mode de reproduction du crabe est de la polygamie mais aussi que des accouplements pouvaient avoir lieu entre crabes d’espèces hôtes distinctes.<p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished