No description available.

The primary aim of this thesis was to establish the mode of action of the heavy metal, copper, on the cardiac physiology of the blue mussel, Mytilus edulis. Exposure of specimens of M.edulis to dissolved copper led to a decrease in heart rate and an increase in heart rate variability (HRV). The concentration of copper causing a 50% reduction in heart rate was found to be 0.8µM, while the concentration causing a 50% increase in HRV was 0.06µM (48 h EC50s). Simultaneous measurements of valve activity indicated that the observed bradycardia was not caused by valve closure. Subsequently, it was considered that copper might directly affect cardiac physiology by disrupting important cellular functions of the heart. Four different ionic currents were identified and characterised in M.edulis ventricular myocytes: two outward potassium currents, a sodium current and a calcium conductance. Copper ions had no effect on the ionic currents of M.edulis heart cells at concentrations shown to inhibit the cardiac activity of whole animals. Clearly, the bradycardia measured in whole animals was not due to a change in the configuration of the ventricular action potential. It was recognised that copper could still directly affect cardiac physiology in mussels by altering excitation-contraction coupling, contractile protein function or myocardial energy production. To determine whether this was the case, recordings of heart contractions from isolated ventricular strips were made using an isometric force transducer. Using isolated strips, inhibition of cardiac activity was only induced by exposure to copper concentrations ≥1 mM. Thus, the fall in heart rate measured in the whole animals dosed with copper could not be attributed to direct cardiomyopathy. Control of the. beating of M. edulis heart is known to be exercised by nerves from the visceral ganglion (VG) that contains both excitatory and inhibitory fibres. Following the removal of the VG (in vivo), exposure to copper had no effect on the heart rate of whole animals as occurred in the initial experiments. This suggests that copper affects the heart rate in M.edulis via a neuronal pathway. The principal cardioexcitatory and cardioinhibitory transmitters in molluscs are thought to be serotonin and acetylcholine, respectively, The effect of copper on the heart rate of M.edulis could not be abolished by depletion of the monoamine content of the animal using reserpine. However, pre-treatment of mussels with α-bungarotoxin considerably reduced the sensitivity of the heart to copper. These results indicated that the influence of copper on the heart of M.edulis might be mediated by a change in the activity of cholinergic nerves to the heart. Acetylcholine is known to have a biphasic action on the heart of M.edulis, low doses depress and high doses excite (the endpoint of both responses resulting in a cessation of the heart beat). In the final experiments of this series, mussels were injected with either benzoquinonium or D-tubocurarine, prior to copper exposure, in an attempt to selectively block the inhibitory or excitatory cholinoreceptors of the heart. Only benzoquinoniuin decreased the susceptibility of the heart to copper, suggesting that copper affects the cardiac activity of blue mussels by stimulating inhibitory cholinergic nerves to the heart. It is suggested that there may be a chemosensory mechanism present in mussels which responds to increased levels of metals in seawater leading to changes in a number of physiological functions. The last result chapter of this thesis examined the effects of the organophosphorous pesticide, dimethoate, on cardiac and acetylcholinesterase (AChE) activity in the common shore crab Carcinus maenas. Cardiac activity was measured non-invasively before and during dimethoate exposure. Heart rates decreased in a concentration-dependent manner. Serial measurements of AChE activity in haemolymph samples taken from crabs before and after exposure indicated that 2 mg 1ˉ¹ dimethoate also significantly reduced AChE activity. The percentage inhibition in AChE activity was correlated with the percentage reduction in heart rate following dimethoate exposure. This suggests that organophosphates may directly affect neuronal control of the heart. These experiments indicate that non-destructive, serial measurements of cardiac activity and AChE activity are valuable biomarkers of organophosphate exposure and adverse effects.

Thesis (M.S.)--Kent State University, 2006. / Title from PDF t.p. (viewed June 21, 2007). Advisor: Rodney M. Feldmann. Keywords: decapoda, crustacea, Jurassic, Romania. Includes bibliographical references (p. 161-181).

Inaug.-diss.--Jena. / Lebenslauf. "Litteratur-verzeichnis": p. 69-71.

Thesis(PH.D.) - Carleton University, 1973. / Also available in electronic format on the Internet.

Inaug.-diss.--Jena. / Lebenslauf. "Litteratur-verzeichnis": p. 69-71.

ix, 113 leaves : ill. ; 29 cm Typescript. (Another copy on microfilm is located in Archives) Thesis (Ph.D.) -- University of Oregon Includes vita and abstract Bibliography: leaves 106-113 University of Oregon theses, Dept. of Biology, Ph.D., 1978

Ph.D. / The Branchiura is a group of ectoparasitic crustaceans which infect mostly fishes. The subclass contains four genera including Argulus, Chonopeltis, Dolops and Dipteropeltis. Despite their reputation as pests our understanding of their biology is meager. In the first part of the study the anatomy and physiology is described. The species studied include Argulus japonicus, Dolops ranarum and Chonopeltis australis. Live specimens of A. japonicus, D. ranarum and Chonopeltis australis were collected, fixed in Todd's fixative and processed for transmission electron microscopy. The results gleaned from A. japonicus and D. ranarum indicated that the ultrastructure and physiology of the cells were similar to the digestive epithelia of free-living copepods. The anterior midgut consists of Resorptive cells (R cells) and the enteral diverticula consist of two cell types including R and Fibril cells (F). The R cells contain lipid droplets and F cells contain rough endoplasmic reticulum indicating that the absorption of nutrients and digestion occurs in the anterior midgut and enteral diverticula. The lipid droplets in both species are large in size and number. Blister cells/B cells and R' (apostrophe) cells occur in the posterior midgut and are involved in the processing of digestive waste. The results from C. australis were different from A. japonicus and D. ranarum and reveal the possible presence of F/R cells with multiple functions of both absorption and enzyme secretion. The cells contain few lipid droplets and instead contain many hexagonal-shaped crystalline structures that are interpreted to be proteinaceous. The differences in diet are thought to be influenced by morphological differences in the feeding appendages. The second part of the study involved the supraoesophageal ganglion or brain of C. australis. This genus is unique among the Crustacea since the antennules are absent. This trait poses implications regarding the brain morphology since particular parts of the brain impart nerves that innervate certain appendages in arthropods. Specifically the deutocerebrum or midbrain innervates the antennules. A study was conducted to discover whether the antennular nerves were absent. Specimens of C. australis were fixed in AFA, sectioned and stained with Heidenhain's AZAN. Results showed that the antennular nerves were absent and the deutocerebrum was smaller in comparison to the other brain segments indicating degeneration. Moreover, C. australis possesses a reduced number of sensory sensilla on its external surface compared to related genera. The loss of antennules does not affect its sensory capabilities in host searching. However, the reduced numbers of sensilla and its feeble swimming capabilities are more likely to reduce its efficiency in host searching.

This thesis examines the relationship between demographic parameters and patterns of energy allocation in a brackish water mysid to test several predictions of life history theory. Populations of N. mercedis subject to different regimes of age-specific mortality allocated energy to reproduction in a manner consistent with predictions based on the maximization of individual fitness. The mechanism by which reproductive allocation was varied was largely through temperature dependent phenotypic variation in the size at maturity which altered size-related components of fitness such as clutch size. N. mercedis in the tidal marshes of the Fraser River delta produced three generations per year which differed in their demographic and life history traits. Summer generations matured at smaller size, carried fewer embryos, had larger eggs, reduced fertility rates, and more even sex ratios than the overwintering generation. Seasonal changes in body size were shown to result from the effects of temperature. Instantaneous per capita birth rates were greatest in the spring and declined to low relatively constant values throughout the summer. Fecundity varied directly with measures of food availability. Size-specific instantaneous mortality rates were higher on small mysids than on larger animals during the spring breeding period but were higher on large animals during the late summer. The mortality rates of neonates were directly related to the abundance of predatory salmon fry and inversely related to food availability, while those of several larger size classes varied inversely with food. Fish predation was generally strongly selective for large mysids. For the mature size classes, the increment in mortality rate with increasing size was positively correlated with environmental temperature, which provided a mechanism through which temperature dependent phenotypic variation in adult size could be selected. The lifetime energy budgets of females from the W, S1, and S2 generations were about 690, 195, and 175 J respectively. The summer and overwintering females differed significantly in their patterns of allocation of assimilated energy. The reproductive effort of the summer females was about 50% greater than that of the W females (12-13% versus 8.5% of the energy budget). My results were in agreement with several of the predictions of life history theory. Reproductive effort was increased when adult mortality rates were high. Reproduction in N. mercedis imposed a real cost in terms of reduced future fecundity and decreased survivorship. Age at maturity decreased and reproductive effort increased during the growth phase of the population. However, no evidence of genetic differentiation was found between the estuarine population and an upriver freshwater population which differed in reproductive characteristics. / Science, Faculty of / Zoology, Department of / Graduate

No description available.