No description available.

Intertidal grazing gastropods play an important role in structuring rocky shore communities. For many years the main food resource to these animals was considered to be epilithic biofilms. This study shows that macroalgae are a more important component of gastropod diets than was previously appreciated and that biofilms contribute surprisingly little to their trophic ecology. Stable carbon and nitrogen isotope analyses were used to examine grazer diets, comparing sources of assimilated carbon and nitrogen in gastropod tissues between moderately wave exposed and sheltered sites in northern and southern Britain. Carbon isotope (δ13C) values of biofilms were considerably lower than those of grazing gastropods at all of the sites examined. The δ13C values of grazer tissues were much more closely related to the carbon isotope values of macroalgae, demonstrating the importance of these foods to intertidal grazing gastropods. Nitrogen isotope values were consistent with this conclusion and reflected differences in the source pools of nitrogen between the two sampling regions. Gut contents analysis was used to directly quantify the diet of the intertidal limpet Patella vulgata in detail. Biofilms and corticated/leathery macroalgae contributed most substantially to patterns of ingested materials and limpet diet was strongly influenced by food availability. Animals from sheltered and northern sites consumed more macroalgae whilst animals from southern sites consumed more biofilm. Stable isotope data from mensurative experiments confirmed the important role of food availability in controlling limpet diets. Data from manipulative caging experiments provided further evidence for this effect and also showed that species identity and interspecific competition influence trophic ecology in intertidal gastropods. Patella depressa isotope values remained different from those of Patella vulgata irrespective of food availability and competition in experimental cages. Stable isotope ratios of Patella vulgata and Littorina littorea, distinct in single species cages, converged towards a common value when held together.

Hydrothermal vent communities exhibit great taxonomic novelty with 88% of species, 51% of genera, and 21% of families new to science. Given the severe physiological barriers to invasion presented by hydrothermalism and the energetic independence of the community due to in situ primary production by chemoautotrophic bacteria, it has been previously proposed that hydrothermal vents may have acted as a refugia for groups of metazoan animals that originated during the Cambrian, Paleozoic, or Mesozoic. The alternate explanation is of rapid change of recent immigrants from the adjacent deep-sea and false taxonomic inflation. Six major groups of hydrothermal vent endemic gastropods exhibit high taxonomic novelty and a lack of known fossils. Discovery of these hydrothermal vent endemic groups has resulted in dramatic changes in how we view the evolution and phylogeny of the Gastropoda, particularly in regards to the novel anatomy of the Neomphalina (Neomphalidae + Peltospiridae). Recent cladistic examinations of gastropod phylogeny using anatomical and morphological characters disagree on the placement and monophyly of the Neomphalina or find few characters supporting their position in the overall gastropod phylogeny. In this dissertation, a molecular systematic investigation of gastropod phylogeny was performed to examine the antiquity of the vent endemic Neomphalina. Twenty-three new D1 domain and thirty new D6 domain DNA sequences of the 28S ribosomal RNA gene were obtained from fresh-frozen and formalin-ethanol preserved specimens. These were combined with previously published molluscan 28S ribosomal RNA sequences for a total of 159 sequences. Gastropod phylogeny was examined using both parsimony and distance-based analyses. The 28S ribosomal RNA gene exhibited saturation of substitutions beyond 15% divergence between sequences, estimated using Kimura’s two-parameter model. Alone, either domain exhibited poor resolution of gastropod phylogeny but together (32 genera only) monophyly of the Neritimorpha, Neomphalina, Vetigastropoda, Patellogastropoda, Caenogastropoda (including Viviparus, Ampullaria, and Campanile), and Heterobranchia (Euthyneura plus Valvata) was supported by bootstrap values. Relationships among these groups could not be resolved due to saturation of substitutions. Evidence of elevated evolutionary rates in the Patellogastropoda conformed to previous studies and confounded analyses. Regardless, the hydrothermal vent Neomphalina exhibited divergence values and phylogenetic novelty equivalent to the other early-Paleozoic radiations, supporting its consideration as a vent refugial phylogenetic relic. 28S ribosomal RNA sequences cannot resolve Cambrian or early Paleozoic radiations of the Gastropoda and use of diverse specimens limits reliability of sub-ordinal relationships due to long-branch attraction. Sequences of 28S ribosomal RNA are best used to examine within-order gastropod relationships due to saturation of substitutions at higher levels and among-order evolutionary rate variation. / Graduate

The aim of this thesis was to identify key neural mechanisms underlying decision making in a model invertebrate system, the pond snail Lymnaea stagnalis. Specifically, this was examined with respect to two decision making processes associated with Lymnaea's feeding behaviour; first a stimulus present/stimulus absent perceptual decision making task for selecting between appetitive and consummatory behaviours, second a behavioural choice between ingestion and egestion. A behavioural paradigm was designed in order to study stimulus present and stimulus absent decision making in Lymnaea. The switch between appetitive and consummatory behaviours was used as a read out of the decision. During stimulus absent decisions, the animal made a judgement about the absence of a sensory stimulus and entered into a period of quiescence. During stimulus present decisions the animal switched from the appetitive behaviour into the consummatory behaviour. The decision about the presence of a stimulus was reliant on the tactile cues from the potential food. Importantly the task was amenable for in vitro preparations and the identification of the decision neurons. A candidate stimulus present decision neuron, the ventral trigger neuron (vTN), was identified in the buccal ganglia. vTN received appropriate sensory input and was able to initiate fictive feeding cycles. vTN was able to initiate fictive feeding cycles via monosynaptic connections with feeding central pattern generator (CPG) interneurons. Development of an in vitro paradigm of the stimulus present and stimulus absent decision provided strong evidence that vTN was a stimulus present decision neuron. A stimulus absent decision neuron was identified as the inhibitory interneuron and member of the feeding CPG, N3t. An in vitro paradigm was used to test interactions of the stimulus present decision neuron with the stimulus absent decision neuron. Goal directed behaviours were also shown to lower the threshold of activity needed for vTN to initiate fictive consummatory behaviours, lowering the sensory threshold needed for stimulus present decisions to be made. The neural mechanism of behavioural choice between ingestion and egestion in Lymnaea was characterised using in vivo and in vitro preparations. A novel motor neuron was identified whose phase of firing activity was selectively shifted between the two behaviours. The interneuronal control of ingestion was identified and consisted of previously identified command-like neurons, whereas the interneuronal control of egestion consisted of novel interneurons located in the buccal ganglia. The two networks showed evidence of both dedicated and multifunctional interneurons. The studies presented in this thesis demonstrate that even within the same relatively simple neural network several distinct mechanisms are utilised for different types of decision. These were identified at the level of individual neurons and their synaptic connectivity. Uniquely in these studies, distinct stimulus absent and stimulus present decision neurons were identified in the perceptual decision task and it was also shown that performing the decision making task facilitates the stimulus present decision. This provides fundamental new insights into the neural mechanisms of decision making. The studies also provide a model system for comparison between a form of decision making studied extensively in mammals (perceptual decision making in a stimulus absent/stimulus present task) and a form studied primarily in invertebrates (behavioural choice between two incompatible behaviours), bridging the gap between invertebrate and vertebrate decision making studies.

Thesis (Ph. D.)--University of Queensland, 2001. / Includes bibliographical references.

No description available.

No description available.

An extensive field survey of 12 duck species yielded two morphologically distinct populations of Typhlocoelum (Digenea: Cyclocoelidae). Studies on the variability of these two populations in conjunction with experimental cross infections provided conclusive evidence that they must be considered as subspecies of Typhlocoelum cucumerinum. A laboratory comparison of their survival strategies revealed that, in the definitive host, Typhlocoelum cucumerinum cucumerinum develops slowly, survives for an extended time and has a high fecundity, whereas Typhlocoelum cucumerinum sisowi develops more quickly, has a shorter longevity and a lower fecundity. In the intermediate host, T. c. cucumerinum develops more slowly than T. c. sisowi. The almost complete segregation of these two subspecies into dabbling and diving ducks in the field may be maintained by an ecological separation of the ducks as well as intrinsic differences between the two host-parasite associations.

Larval development of Berthella californica, a pleurobranchoidean heterobranch from the Northeastern Pacific, is described using histological sectioning, SEM, TEM, and immunolabelling. Current phylogenetic hypotheses place the Pleurobranchoidea as sister to all nudibranchs, or as sister to only the anthobranch nudibranchs. Deciding between these alternatives is difficult due to extensive homoplasy among heterobranchs. Analysis of larval morphology may help resolve this issue by identifying additional phylogenetically informative characters. Larval development has been well documented for many nudibranchs, but there are few studies on pleurobranchoideans. Larvae of B. calfornica dissolve internal shell whorls, a trait uniquely shared with nudibranch larvae. Additionally, mantle fold tissue inflates and reflects dorsally during metamorphosis to form the notum, which also occurs in anthobranchs. B. californica possesses several unusual developmental traits, as revealed by a review of current knowledge of heterobranch development. Morphological characters of B. californica larvae support hypotheses of nudibranch paraphyly and the clade Pleuroanthobranchea.

Id30/2/2727The neakshore prosobranch gastropod epifauna of Signy Island, South Orkney Islands. Picken,-.G.B.The prosobranch gastropod epifauna associated with a mature algal community on a rocky substrate in the depth range 2-12 m was studied at Signy Island, South Orkney Islands, Antarctica (60°S.43°W). Quantitative samples were collected by divers at monthly intervals from April 1975 to March 1977, using an air-lift suction sampler. Thirty-one prosobranch species were found in a total sample of about 138,000 animals; 7 species were undescribed, and 10 were new to the South Orkney Islands. Small, cryptic "Rissoids" such as Eatoniella kerguelenensis, E.caliginosa and Ovirissoa adarensis were numerically dominant, but the limpet Nacelle (Patinigera) concinna was dominant in terms of biomass. Mean prosobranch density was 4,591 individuals 1r2. and mean biomass 17.1 g dry tissue m2. Diversity was high throughout most of the depth range and the assemblage was both complex and stable. Ten species developed non-pelagically by means of large yolky eggs laid on algal fronds or stones in the sub-littoral. Spawning periods were prolonged and largely aseasonal, and development times were long. Recruitment of juveniles was also aseasonal, though a peak of recruitment was observed in one species during the Austral spring. Laevilacunaria antarctica shows several characteristics of 'K-selection'; it develops non-pelagically, grows slowly and lives for more than one year. Other weed-dwelling prosobranchs at Signy Island which develop non-pelagically probably also tend towards 'K-selection'. The limpet Nacella develops pelagically after adults congregate briefly in summer to form spawning "stacks" of 3-6 individuals. Nonetheless, the species shows several 'K-selection' traits, particularly very slow growth and deferred maturity, and tends towards 'K-selection'.Collections from other sites to 80 m depth off Signy Island yielded 20 more species; 13 of these were undescribed and 5 were new to the South Orkney Islands. The study has shown that the prosobranch fauna of the South Orkney Islands was incompletely known, and that a greater understanding of the distribution, endemism and origins of the Antarctic prosobranch fauna will not be possible until more key sites are investigated in greater detail.