Echinoids (sea urchins and sand dollars) undergo thyroid hormone (TH) regulated larval development and several species can endogenously synthesize these hormones. Although iodine is the essential component for TH synthesis, nothing is known about iodine uptake mechanisms in echinoids. This thesis primarily aimed to characterize integumental iodine uptake in larvae (echinoplutei) of the purple sea urchin Strongylocentrotus purpuratus. The two mechanisms considered were: iodine uptake via sodium dependent transport utilizing orthologs of vertebrate sodium iodide symporter (NIS) and apical iodide transporter (AIT) versus hydrogen peroxide dependent diffusion (PDD) of iodine. Pharmacology and radioiodine (125I) experiments characterized the effects of various compounds on echinoid iodine uptake. The results demonstrate that purple sea urchin echinoplutei acquire iodine from feeding on microalgae and through integumental transfer. Integumental transfer of iodine is inhibited by cyanide and is temperature dependent. Echinoplutei are not affected by perchlorate exposure demonstrating that NIS/AIT is not involved in S. purpuratus iodine uptake. NIS and AIT are both members of the Sodium Solute Carrier 5 (SSF5) transporter family and phylogenetic analysis of various vertebrate and invertebrate SLC5 members (obtained through BLAST searches) indicated that NIS-like transporters might be a vertebrate synapomorphy. Hydrogen peroxide exposure and oxidative stress induced an increase in iodine influx, whereas reducing agents and peroxidase inhibitors disrupted iodine uptake supporting a PDD-based iodine uptake model. In situ hybridization, immunohistochemistry and real time-PCR analysis demonstrate that the sea urchin dual oxidase 1 (Udx1) (an NADPH oxidase that produced hydrogen peroxide) is expressed throughout all stages of larval development in both S. purpuratus and Lytechinus variegatus specifically occurring in epithelial cells. These findings are the first data to demonstrate Udx1 presence and potential activity outside of fertilization and embryogenesis in echinoplutei. The expression patterns and pharmacological results make Udx1 an attractive candidate for involvement in integumental iodine transfer through PDD. These data provide the first evidence for PDD in an animal. The results also suggest that NIS/AIT may be a vertebrate synapomorphy and PDD of iodine across the integument may be widespread across organisms. Future characterization of iodine uptake mechanism in diverse taxa will address this issue. / Studies were funded by the Natural Sciences and Engineering REsearch Council (NSERC) to A.H. [grant number 400230], Equipment purchased with funding from the Caiadian Foundation for Innovation CFI and NSERC [grant number 400587] to A.H.

This diploma thesis is focused on morphological studies and taxonomic analyses of small regular and irregular echinoids found at the Nebužely locality; at this locality clastic sediments of Teplice Formation of Bohemian Cretaceous Basin are exposed. Presence of the belemnite Praeaxtinocamax bohemicus makes possible to assign the outcrop to late Turonian. Detailed morphological study of more than one hundred specimens enabled to distinguish four echinoids species (Echinogalerus, Glyphocyphus, Nucleolites, Phymosoma), less favourably preserved and/or very limited material is classified as belonging to two orders (Cidaroida, Holectypoida) and one family (Phymosomatidae), respectively. The next part of the thesis contains a possible palaeoecological reconstruction of the environment at the studied locality. Based on bathymetrically indicative molluscs, a shallow−water palaeoenvironment is suspected for this locality. Key words: echinoid, Bohemian Cretaceous Basin, Turonian

No description available.

No description available.

Climate change is predicted to affect the larval stages of many marine organisms. Ocean warming can reduce larval survival and hasten larval development, whereas ocean acidification can delay larval development. Ocean acidification is especially concerning for marine organisms that develop and grow calcified shells or skeletons in an environment undersaturated with calcium carbonate minerals. This study assessed the effects of ocean warming and acidification on the fertilization and larval development of the green sea urchin, Lytechinus variegatus, a tropical species common in Florida and the Caribbean. After spawning, gametes were fertilized and embryos/larvae were reared at: 1) 28°C and pH 8.1 (control), 2) 28°C and pH 7.8 (ocean acidification scenario), 3) 31°C and pH 8.1 (ocean warming scenario), and 4) 31°C and pH 7.8 (ocean warming and acidification scenario). Exposure to acidified conditions had no effect on fertilization, but delayed larval development, stunted growth and increased asymmetry. Exposure to warm conditions decreased fertilization success at a high sperm to egg ratio (1,847:1), accelerated larval development, but had no significant effect on growth. Under exposure to both stressors (ocean warming and acidification), larval development was accelerated, but larvae were smaller and more asymmetric. These results indicate that climate change will have a serious impact on the larval development and growth of the green sea urchin, L. variegatus, and may negatively affect its persistence.

Disturbances, such as mass pollution events, threaten the health of vulnerable ecosystems. Recent media attention has focused on the devastating mass oil spills, but daily petroleum input from recreational and commercial ship bilge release has been overlooked. The focus of this study was the effect of petroleum products found in bilge water on fertilization success and larval viability of two sea urchin species, Lytechinus variegatus and Eucidaris tribuloides. Unlike other pollutant studies that have focused on sperm characteristics and concentrations, I chose to examine how egg integrity was compromised by petroleum products. Scanning electron microscopy revealed eggs were degraded when exposed to low levels of these pollutants. Of the three, oil was the most detrimental to Lytechinus variegatus fertilization, while gas was highly detrimental to Eucidaris tribuloides. Dosing the eggs for only two hours before introducing sperm demonstrated significant reduction in fertilization and larval survivorship. These data suggest that even relatively low and brief exposure to petroleum pollutants can have devastating effects on sea urchin reproductive success. New regulations may need to be considered when determining the safe petroleum concentration in bilge discharge.

The quantification of disparity is an important aspect of recent macroevolutionary studies, and it is usually motivated by theoretical considerations about the pace of innovation and the filling of morphospace. In practice, varying protocols of data collection and analysis have rendered comparisons among studies difficult. The basic question remains, How sensitive is any given disparity signal to different aspects of sampling and data analysis? Here we explore this issue in the context of the radiation of the echinoid order Spatangoida during the Cretaceous. We compare patterns at the genus and species levels, with time subdivision into subepochs and into stages, and with morphological sampling based on landmarks, traditional morphometrics, and discrete characters. In terms of temporal scale, similarity of disparity pattern accrues despite a change in temporal resolution, and a general deceleration in morphological diversification is apparent. Different morphometric methods also produce similar signals. Both the landmark analysis and the discrete character analysis suggest relatively high early disparity, whereas the analysis based on traditional morphometrics records a much lower value. This difference appears to reflect primarily the measurement of different aspects of overall morphology. Disparity patterns are similar at both the genus and species levels. Moreover, inclusion or exclusion of the sister order Holasteroida and the stem group Disasteroida in the sampled morphospace did not affect proportional changes in spatangoid disparity. Similar results were found for spatangoid subclades vis-à-vis spatangoids as a whole. The relative robustness of these patterns implies that the choice of temporal scale, morphometric scheme, and taxonomic level may not affect broad trends in disparity and the representation of large-scale morphospace structure.

Quels sont les grands patrons de distribution des espèces et quels sont les facteurs qui les contrôlent? Ces questions sont au cœur des problématiques macroécologiques et prennent un intérêt tout particulier au regard du réchauffement climatique global actuel. L’objectif principal de ce travail de thèse était de déterminer les patrons de distribution actuels des espèces d’oursins antarctiques et subantarctiques à l’échelle de l’océan Austral et de mettre en évidence les facteurs qui contrôlent ces distributions. La modélisation des niches écologiques d’une vingtaine d’espèces d’oursins a permis de mettre en évidence deux grands patrons de distribution : (1) un premier représenté par les espèces dont la distribution n’est pas limitée au sud du Front Polaire et s’étend des côtes antarctiques aux zones subantarctiques et tempérées froides et (2) un deuxième constitué d’espèces restreintes à la zone antarctique. Au sein de ces deux patrons, cinq sous-patrons ont également pu être défini sur la base de différences de distribution latitudinale et bathymétrique entre groupes d’espèces. Cette approche biogéographique par modélisation de niche écologique a été complétée par l’analyse de similarité de l’ensemble des faunes d’oursins, de bivalves et de gastéropodes, au niveau spécifique et générique, entre biorégions de l’océan Austral. Cette analyse démontre qu’il existe chez les oursins et les bivalves des connexions fauniques entre l’Amérique du Sud et les zones subantarctiques ainsi qu’une séparation entre l’Est et l’Ouest antarctique. Au contraire, les faunes de gastéropodes subantarctiques montrent des affinités plutôt antarctiques que sud-américaines, l’Antarctique ne formant qu’une unique province pour ce clade. Ces différences entre clades sont interprétées comme étant le résultat d’histoires évolutive et biogéographique distinctes entre oursins et bivalves d’une part et gastéropodes d’autre part. L’hypothèse d’une réponse évolutive différente des clades aux changements environnementaux survenus au cours du Cénozoïque est avancée. Enfin, l’existence de connexions fauniques trans-antarctiques est mise en évidence dans l’étude des trois clades ; celles-ci sont interprétées comme le résultat de la dislocation de la calotte ouest-antarctique et l’ouverture de bras de mer trans-antarctiques au cours du Pléistocène. Parmi les paramètres environnementaux utilisés dans la modélisation des niches écologiques, les résultats montrent que trois paramètres jouent un rôle majeur dans la distribution des oursins : la profondeur, la couverture de glace et la température des eaux de surface. Toutefois, l’importance relative de ces paramètres diffère selon les espèces d’oursins étudiées. L’étude du genre Sterechinus souligne tout particulièrement ces différences. En effet, l’espèce S. neumayeri est plus sensible aux conditions environnementales qui prédominent près des côtes antarctiques (température des eaux de surface et couverture de glace), alors que S. antarcticus semble être beaucoup moins contraint par ces mêmes paramètres. La distribution potentielle de S. antarcticus est d’ailleurs beaucoup plus étendue en latitude. Cependant, S. antarcticus n’est pas présent sur l’ensemble de son aire de distribution potentielle, ceci pouvant être expliqué alternativement par le résultat (1) de facteurs océanographiques (rôle de barrière biogéographique joué par le Front Polaire), (2) d’interactions biotiques (phénomènes de compétition inter-spécifique) et (3) du contexte temporel (colonisation toujours en cours). / What are the forcing factors and main patterns of species distribution? This question is the core of macroecological issues and is of particular interest in the present context of global warming. The main objectives of this thesis were to determine the current distribution patterns of Antarctic and sub-Antarctic echinoid species at the scale of the whole Southern Ocean and to highlight the forcing factors that control them. The ecological niche modelling of 19 echinoid species showed that distribution is mainly structured in two patterns: (1) a first one represented by species that are not limited to the south of the Polar Front and distributed from the Antarctic coasts to the sub-Antarctic and cold temperate areas, and (2) a second one with species restricted to the Antarctic area. Within these two main patterns, five sub-patterns were also identified that depend on differences in the latitudinal and depth range of species groupings. In addition to this approach of biogeography by ecological niche modelling, a similarity analysis of echinoid, bivalve and gastropod fauna between bioregions of the Southern Ocean was performed at species and genus levels. This analysis reveals faunal connections between southern South America and sub-Antarctic areas in echinoids and bivalves, along with a partition between the East and West Antarctic. On the contrary, sub-Antarctic gastropod fauna show Antarctic rather than South American affinities and the Antarctic form a sole and unique province in this clade. These differences between clades are interpreted as the result of distinct biogeographic and evolutionary histories between echinoids and bivalves on the one hand, and gastropods on the other hand. The proposed hypothesis is that clades developped different evolutionary responses to the environmental changes that occurred during the Cenozoic. Finally, in the three clades, trans-Antarctic faunal connections are shown and interpreted as a result of West Antarctic Ice Sheet collapses and the setting up of trans-Antarctic sea-ways during the Pleistocene. Among the environmental parameters used for the ecological niche modelling, results show that the three following parameters play the main part in echinoid distribution: depth, sea-ice cover and sea surface temperature. However, the relative importance of these parameters depends on the species under studies. These differences are particularly emphasized in the case study of the genus Sterechinus. The species S. neumayeri is indeed the most dependent on environmental conditions that prevail along the Antarctic coasts (sea surface temperature and sea-ice cover), while S. antarcticus doesn’t seem to be so much under the control of these parameters. Accordingly, the potential distribution of S. antarcticus in latitude is the most extended. However, S. antarcticus is not present over the whole area of its potential distribution, what can be explained as the result of either (1) oceanographic factors (role of the Polar Front as a biogeographical barrier), (2) biotic interactions (inter-specific competition) or (3) the temporal context (still ongoing colonization).

Les modifications environnementales qui affectent aujourd'hui les milieux marins recouvrent des problématiques scientifiques et sociétales majeures, d'autant que ces changements devraient s'accélérer au cours du 21ème siècle. Comprendre et anticiper la réponse de la biodiversité marine à ces changements représente un enjeu scientifique d'actualité. Les approches biogéographiques et macroécologiques constituent un cadre scientifique dans lequel il est possible d'étudier, de décrire, et de comprendre les motifs de distribution des espèces à large échelle et d'estimer leur évolution possible face aux changements environnementaux. C'est notamment le cas dans l'océan Austral où les effets du changement climatique se font déjà sentir et où les modifications environnementales associées pourraient avoir des effets profonds sur la structure et le fonctionnement des écosystèmes. Malgré de récents efforts d'échantillonnage, nos connaissances sur la distribution des espèces dans l’océan Austral comptent encore de nombreuses lacunes attribuables au caractère récent des découvertes, à l'isolement et à l'éloignement de cet océan d'accès difficiles. Dans ce contexte, les objectifs de cette thèse consistaient à mieux comprendre les motifs de distribution d'espèces à l’échelle de l’océan Austral, à mettre en évidence les facteurs qui en sont à l’origine et enfin, à évaluer l’impact du changement climatique sur leur distribution. Pour cela, différents types de modèles de niche écologique (MNE) ont été employés. Les échinides (oursins), organismes communs des communautés benthiques de l’océan Austral ont servi de modèle d'étude pour ce travail. / Current environmental changes, which impact marine environments, cover major scientific and societal issues, especially as these environmental changes are expected to accelerate along the 21st century. Understanding and forecasting the response of marine biodiversity to these changes is a pregnant scientific issue. Biogeographic and macroecological approaches provide a scientific framework for that purpose. They allow describing and understanding species distribution patterns at large spatial scale as well as estimating their potential shift with regards to environmental change. This is particularly true in the Southern Ocean, where the effects of climate change are already occurring and where environmental changes could have a deep and manifold impact on the structure and functioning of marine ecosystems. Despite recent sampling efforts, our knowledge of the Southern Ocean species distributions still faces many shortcomings due to the rather recent discovery of this ocean, its isolation and remoteness along with difficult access conditions. In this context, the aims of this thesis are to better understand the factors that drive species distribution patterns at the Southern Ocean scale, and to assess the impact of climate change on their distribution. For this purpose, different types of Species Distribution Models (SDM) have been used. Echinoids (sea urchins), which are common organisms of benthic communities in the Southern Ocean, have been used as a biological model for this work.

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