Kiel, Univ., Diss., 2002. / Computerdatei im Fernzugriff.

A population of threespine sticklebacks (Gasterosteus aculeatus) infected with the cestode parasite S. solidus was studied to determine the effects of the parasite on stickleback reproductive. success, mortality rates, and swimming ability. The S. solidus infection increased stickleback mortality rates in 'natural' mortality, and in stressed mortality (low oxygen, high temperature) experiments. Infections of S. solidus at intensities of 30% of the stickleback body weight or greater, clearly affect the sticklebacks ability to swim. How infections at this or lesser levels effect predation on parasitized sticklebacks was not established. The effects of S. solidus on stickleback reproductive success were found to be minimal in this study, chiefly because the stickleback breeding season is essentially complete before the S. solidus infection becomes severe. / Science, Faculty of / Zoology, Department of / Graduate

University, Diss., 2002--Kiel.

To date, most studies of the cestode cuticle have been carried out on adult worms and in no instance has an attempt been made to correlate ultrastructural and histochemical observations. The present study was designed to obtain information on both the histochemical composition and the ultrastructure of the plerocercoid cuticle of the pseudophyllidean cestode Schistocephalus solidus (Müller, 1776) and to study any changes which might occur during plerocercoid differentiation. Initially, this work has demonstrated that the plerocercoid tegument of S. solidus is of the same fundamental type as that of previously described cestodes. An outer anucleate but cellular region (the cuticle) is connected by cytoplasmic tubes to nucleated tegumental cells lying in the parenchyma. It has been shown that the pore canals of S. solidus are different from any described for other cestodes and it is suggested on morphological grounds that they may function in a secretory capacity. In addition, the pore canals provide a direct connection between certain parenchymal cells and the external medium. Papilla-like cuticular processes on the cuticular surface have been described and both adhesive and absorptive functions are suggested for these structures. It has been shown that the cuticular processes are not present in the smallest forms studied but rather appear at about the same time as the worm becomes infective. Changes in the histochemical and ultrastructural composition of the cuticular matrix have been described. It is probable that increased plerocercoid growth is accompanied by a change in cuticular composition from a more proteinaceous state to one which is largely carbohydrate. A surface sulphomucin-basic protein complex has been described and partially characterized. Possible functions have been suggested for this layer. RNA as well as acid and alkaline phosphatases were found in the cuticle and the possible significance of these substances in cuticular synthetic activities is considered. It is suggested that plerocercoid cuticular differentiation may consist of two phases: (1) an initial phase in which various mechanisms are elaborated to allow survival in the vertebrate intestine, and (2) a second phase in which the plerocercoid is modified to permit prolonged growth in the stickleback coelom. / Science, Faculty of / Zoology, Department of / Graduate

<p>In the freshwater copepod, <i>Macrocyclops albidus,</i> food availability, rearing conditions and tapeworm infection clearly affected various life-history traits and their trade-offs. I found that low food availability clearly constrained resource allocations to several life-history (often phenotypically plastic) traits, whereas high food availability either allowed for adjustments in resource allocation patterns or allowed resources to be allocated to several traits without apparent trade-offs. </p><p>Both male and female copepods allocated resources according to food availability; developing more slowly and achieving smaller adult body size when food was scarce. When food availability was low females were constrained and produced fewer eggs (in total and per clutch), and started reproduction later than females with more food available. Males under low food availability allocated relatively more to spermatophore size (current reproduction) with decreasing body size. In contrast, when food availability was high males allocated resources to body size as well as spermatophore size. Overall, at maturity, copepods of both sexes were more similar in size than in age, suggesting that large body size was more important for fitness than fast development. </p><p>In nature the prevalence of copepods infected with cestode tapeworms was found to be low (0-3%). Female copepods, experimentally infected with the cestode <i>Schistocephalus solidus</i>, showed lower overall fecundity, especially when food availability was low. However, infected females produced a larger proportion of their life-time egg production early in life than non-infected females. This might be an adaptation to reduce future fitness costs of infection. Females grown under bad rearing conditions, but with high food availability, produced their first clutch earlier than females grown under good rearing conditions, indicating an adjustment in timing of reproduction. These findings contribute to our fundamental evolutionary understanding of how environmental conditions interact with life-history traits.</p>

In the freshwater copepod, Macrocyclops albidus, food availability, rearing conditions and tapeworm infection clearly affected various life-history traits and their trade-offs. I found that low food availability clearly constrained resource allocations to several life-history (often phenotypically plastic) traits, whereas high food availability either allowed for adjustments in resource allocation patterns or allowed resources to be allocated to several traits without apparent trade-offs. Both male and female copepods allocated resources according to food availability; developing more slowly and achieving smaller adult body size when food was scarce. When food availability was low females were constrained and produced fewer eggs (in total and per clutch), and started reproduction later than females with more food available. Males under low food availability allocated relatively more to spermatophore size (current reproduction) with decreasing body size. In contrast, when food availability was high males allocated resources to body size as well as spermatophore size. Overall, at maturity, copepods of both sexes were more similar in size than in age, suggesting that large body size was more important for fitness than fast development. In nature the prevalence of copepods infected with cestode tapeworms was found to be low (0-3%). Female copepods, experimentally infected with the cestode Schistocephalus solidus, showed lower overall fecundity, especially when food availability was low. However, infected females produced a larger proportion of their life-time egg production early in life than non-infected females. This might be an adaptation to reduce future fitness costs of infection. Females grown under bad rearing conditions, but with high food availability, produced their first clutch earlier than females grown under good rearing conditions, indicating an adjustment in timing of reproduction. These findings contribute to our fundamental evolutionary understanding of how environmental conditions interact with life-history traits.

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