No description available.

Cephalopod populations typically display life-history traits such as semelparity, fast growth, and rapid response to environmental variation. The short lifespan of most squid species means that populations typically consist of single non-overlapping generations; the success of future generations therefore depends upon the ability of present generations to produce viable offspring. Pronounced inter-annual fluctuations in cephalopod population sizes reflect, at least in part, variability during the embryonic, hatchling and juvenile phases. As post-hatch survival is critically dependent upon the successful capture and consumption of zooplanktonic prey, variability in hatchling morphology (e.g. size, shape, presence of abnormality) and physiology (e.g. thermal tolerance) are likely to exert significant influence upon survival. This thesis investigates embryonic variability in two temperate loliginid squid: the Northern Hemisphere Loligo forbesi Steenstrup 1856 and the Southern Hemisphere Sepioteuthis australis Quoy and Gimard 1832. Developmental variability in L. forbesi and S. australis largely manifests via chromatophore pattern. The plasticity and thermal sensitivity of chromatophore characters exceed those of standard morphological characters (e.g. body shape and size). Elevation of incubation temperature is associated with reduced chromatophore number and heightened pattern asymmetry. Correlation between temperature and hatchling phenotype is sufficiently strong to permit estimation of mean thermal history from measure of multiple chromatophore and morphological characters. Increased water temperature is associated with increased frequency of morphological abnormality. In situ assessment of embryonic development in S. australis indicates ~89% egg viability within egg strands. Significant intra-seasonal differences in incidence of mortality and abnormality appear to reflect changes in environmental conditions. Embryos reared under fluctuating (field) thermal conditions grow faster than those reared under stable (aquaria) thermal conditions. Despite variation in size-at-hatch, no concomitant differences are observed in mantle muscle structure. The results of this thesis indicate no significant relationship between hatchling phenotype and underlying physiological processes (i.e. plasticity). I discuss the idea that quantification of embryonic development in cephalopods has relevance to both fisheries management and biomonitoring.

The structural colors, produced by leucophore and iridophore cells, are important for cephalopod camouflage; however, their scattering properties have not been very well studied. These colors are mainly due to the scattering of the specific small scatterers inside of the cell. In this work we will summarize the theories and the numerical methods used to solve both the scattering problems for one scatterer and a collection of such scatterers. The reflection spectrum of iridophores is shown to depend on both particle orientation and incident angle of the light. The leucophores are shown to be a white Lambertian surface. Therefore, starting from the structure of the cells, we can predict their color appearance in the skin. This work provides a general framework for the study of the structural color of cephalpods, and can be applied to many species with different cell structures.

Cephalopods provide forage to a wide range of predators in marine food-webs. Despite their ecological importance, a basic understanding of the mechanisms controlling predation risk and demand is lacking. This is true of one of the most common species of squid found in the northwest Atlantic, the longfin inshore squid (Loligo pealeii). In this dissertation, I address this shortcoming by investigating the role that size and behavior play in influencing squid’s vulnerability to predation. I used long-term food habits, population survey, and commercial landings data, to quantify size-based patterns of predation respective to 25 species of predators. Additionally, I estimated the amount of overlap between predatory consumption and the fishery catch for squid by size. I found that finfish and elasmobranchs generally consumed juvenile and sub-adult squid, while marine mammals primarily targeted adults. Consequently, marine mammals had the highest overlap with the fishing industry for squid size resources. Although large squid were not common in predator diets, predators did not appear to be gape-limited when feeding on squid. This suggested that other factors, including behavior, were important in shaping size-based patterns of predation. I used a laboratory-based approach to quantify attack and capture behaviors towards squid by two predators representing contrasting foraging tactics. Bluefish (Pomatomus saltatrix) and summer flounder (Paralichthys dentatus) were chosen as cruising and ambush predators, respectively. Patterns in attack rates suggested that sizeselection on squid was constrained by passive processes rather than active choice in both predators. Size-dependent profitability functions were calculated by combining capture success rates, handling times, and relative prey mass, and determined that bluefish was the more efficient predator of squid. Lastly, I evaluated the occurrence and effectiveness of anti-predator responses used by squid in the presence of bluefish and flounder. Squid behavior depended on the type of predator present, and the survival value of primary and secondary defense behaviors differed during interactions with each predator. The results of this project are intended to improve the quality of management of squid and their predators by providing a better understanding of predator-prey interactions in the northwest Atlantic.

This thesis establishes baseline information on the distribution, biogeographical variability, habitat preference and trophic interactions for the most common Canadian Arctic cephalopod species: Gonatus fabricii, Rossia moelleri, R. palpebrosa, Bathypolypus species complex and Cirroteuthis muelleri. Records of Arctic cephalopods and their predators were compiled and areas of interest within the Canadian Arctic were identified. Morphometric analyses of G. fabricii and R. palpebrosa identified potential populations and described the key morphometric characters associated with each population. G. fabricii separated into four groupings: Hudson Strait, Ungava Bay, Baffin Bay/Greenland and Disko Bay, while St. Lawrence R. palpebrosa were distinguishable from Arctic samples. Principal component analysis (PCA) was the preferable multivariate method for population analyses. Stable isotope analyses of δ13C identified cephalopod habitat preferences and potential ontogenetic habitat shifts while stomach content analyses, δ15N values and mixing models provided trophic information, including the first descriptions of R. palpebrosa and C. muelleri prey items. / October 2015

La seiche commune Sepia officinalis est un Mollusque Céphalopode présent sur les côtes Normandes. En Baie de Seine, elle représente la troisième espèce visée par les flottilles hauturière et côtière, ce qui en fait une ressource économique importante pour la région. Dans un contexte de protection de la ressource, l’étude et la compréhension des mécanismes liés à la reproduction représentent un objectif majeur. Cette étude est donc focalisée sur les mécanismes régulateurs de la ponte, et en particulier sur les facteurs impliqués dans l’émission des ovocytes. Des recherches antérieures effectuées au laboratoire ont mis en évidence un contrôle multifactoriel du processus de ponte, avec trois niveaux de régulation. (i) Les neuropeptides sont impliqués dans la perception des paramètres environnementaux, (ii) les facteurs ovariens assurent la régulation paracrine du tractus génital, et (iii) les phéromones sexuelles, tout en interférant avec la ponte, sont suspectées de jouer un rôle important dans le comportement des géniteurs associé à la reproduction. Cette thèse met en lumière le rôle de 2 familles de neuropeptides identifiées récemment : les CCAPs et les FLGamides (ou So-orcokinines B). Ces deux familles participent au transport de l’ovocyte et à la sécrétion capsulaire en agissant sur l’activité contractile du complexe oviducte/glande de l’oviducte et des glandes nidamentaires principales. Ces neuropeptides sont par ailleurs suspectés de jouer un rôle dans la biosynthèse des protéines vitellines et des protéines capsulaires. Parallèlement, des phéromones sexuelles sont exprimées par la glande de l’oviducte et sécrétées avec les protéines capsulaires. Des travaux antérieurs ont permis de caractériser des produits d’expression issus de clivages de type prohormone convertase. Dans cette nouvelle étude, un second mode de clivage a été mis en évidence avec l’identification de produits de clivage de masse moléculaire supérieure à 20 kDa. L’un de ces produits, la phéromone beta, a été produit en système recombinant mais son activité biologique sur l’appareil génital mâle et sur l’oviducte n’a pas été démontrée. Quant aux tests comportementaux, ils n’ont pu être exploités du fait d’un nombre d’animaux testés trop restreint. Enfin, une approche transcriptomique comparative et différentielle réalisée à partir de l’organe olfactif mâle et du pavillon de l’oviducte a permis d’identifier un récepteur candidat à la liaison avec les phéromones sexuelles / The common cuttlefish (Sepia officinalis) is a Cephalopod mollusk found on the Normandy coasts. In the Bay of Seine, it is the third species targeted by offshore and coastal fleets, so it is an important economic resource for the whole region. In a context of resource protection, the study and understanding of its reproductive mechanisms is a major objective. This study is therefore focused on the regulatory mechanisms of egg-laying, and in particular on the factors involved in the release of oocytes. Previous research in the laboratory demonstrated multifactorial control of the egg-laying process, with three levels of regulation: (i) neuropeptides involved in the perception of environmental cues, (ii) ovarian factors providing paracrine regulation of the genital tract, and (iii) sexual pheromones, which are implied in egg-laying and are suspected to play a determining role in the reproductive behavior. This thesis highlights the role of two families of recently identified neuropeptides called CCAPs and FLGamides (or So-orcokinins B). These two families participate in oocyte transport and in egg capsule secretion by acting on the contractile activity of the oviduct/oviduct gland complex and of the main nidamental glands. These neuropeptides are also suspected to play a role in the biosynthesis of yolk and capsular proteins. At the same time, sex pheromones are expressed by the oviduct gland and secreted along with capsular proteins. Previous work made it possible to characterize expression products resulting from cleavages of the prohormone convertase type. In this new study, a second mode of cleavage is highlighted, evidenced by the identification of cleavage products with MWs greater than 20 kDa. One of these products, beta pheromone, was produced in a recombinant system but its biological activity on the male reproductive system and on the oviduct was not demonstrated. As for behavioral tests, they were not exploited because the number of animals tested was too small. Finally, a comparative and differential transcriptomic approach of the male olfactory organ and the oviduct pavilion evidenced a candidate receptor expected to bind to sex pheromones

No description available.

Nearly all deep-sea cephalopod life history studies have been completed by examination of specimens collected in the wild. Much of this work is like piecing together a puzzle; knowledge of the life history of many species remains fragmented and hence, taxonomically and phylogenetically confused. Molecular approaches and sequencing technologies are powerful tools for deciphering wild-type cephalopod life history and population dynamics. Use of molecular markers offers additional certainty for identifying specimens damaged during deep-sea collections and can elucidate often cryptic, intra- and interspecific diversity. The research presented in this study assessed broad genetic patterns of biodiversity in deep-sea cephalopods from the Gulf of Mexico and northwestern Atlantic Ocean. This study has two key objectives: [1] to examine intraspecies variation among regionally disjunct subpopulations, comparing collections separated by the Florida Peninsula, and [2] to examine intraspecies variation within deep-sea cephalopods in the Gulf of Mexico. Through Sanger sequencing marker genes COI, 16S rRNA, and 28S rRNA, this study has generated a genetic baseline characterization of deep-sea cephalopods in the Gulf of Mexico, assessed intraspecies genetic variation, and linked morphological identification with DNA barcodes, testing morphological hypotheses of species identification and naming. Results of investigating intraspecies variation within regionally disjunct subpopulations reveal there is no regional distinction between the Gulf of Mexico subpopulations of Vampyroteuthis infernalis, Pyroteuthis margaritifera, and Cranchia scabra, and the Bear Seamount subpopulations in the northwestern Atlantic Ocean. Results of investigating intraspecies variation within the Gulf of Mexico displayed potential for cryptic species, novel sequence records, and large expansions to sequence records for species known to inhabit the Gulf of Mexico. Analysis of intraspecies variation within the Gulf of Mexico facilitated identification of damaged specimens used for this study, but also revealed GenBank database issues of misidentified records, and outdated nomenclature in accession records. Because cephalopods play a central role in most oceanic ecosystems, characteristics like a short average life span and a rapid growth rate mean that cephalopod populations have the potential to serve as an invaluable reflection of ecosystem change.

No description available.