Inaug.-diss.--Leipzig. / Includes bibliographical references.

Inaug.-diss.--Leipzig. / Bibliographical footnotes.

I STUDIES ON THE GLOMERULAR FILTRATION RATE OF RAINBOW TROUT (SALMO GAIRDNERI) Upon adaptation of rainbow trout to 80% sea water, the glomerular filtration rate, as measured by the method of inulin clearance, was reduced from 156 ± 8.9 to 10.0 ± 2.6 ml./kg. body weight/day. Return to fresh water after one month in sea water was accompanied by a rapid re-establishment of the high glomerular filtration rate. This lability of the glomerular filtration rate in the trout is probably an important factor contributing to the reduction of urine flow associated with the adaptation of the euryhaline form to sea water. The effects of adrenocortical and mammalian neurohypophysial hormones on the glomerular filtration rate were studied. Vasopressin and oxytocin, when administered either separately or together, significantly increased the filtration rate, aldosterone had no effect, while corticosterone caused a significant reduction. II STUDIES ON ELECTROLYTE EXCRETION IN THE GREEN TURTLE (CHELONIA MYDAS) The extracellular concentrations of sodium and potassium in the marine turtle, Chelonia mydas mydas, were unchanged after adaptation to a fresh water environment. At the same time the urinary concentrations of these ions were significantly reduced. In addition, the "salt glands" of fresh water adapted juvenile turtles showed a 38% regression in absolute weight. Feeding and saline-loading of sea water adapted turtles elicited rates of sodium and potassium excretion greatly in excess of those possible via the kidney. Failure to detect significant changes in these rates following occlusion of the cloaca further indicated that the major site of electrolyte excretion after feeding or saline-loading was the salt gland. Suppression of adrenocorticosteriod synthesis by treatment with amphenone "B" immediately after feeding or saline-loading reduced the excretion of sodium and potassium to unfed or non-loaded levels. The normal pattern of sodium excretion but not of potassium excretion could be restored in the amphenone-treated animals by the simultaneous administration of corti-costerone. The significance of the ingestion of sea water is discussed in relation to the high electrolyte intake associated with the diet of these turtles. / Science, Faculty of / Zoology, Department of / Graduate

Abnormal mitotic divisions and chromosomal aberrations were observed in onion root-tip cells treated with various concentrations of sunflower seed oil and for varying times. All treatments induced similar chromosomal aberrations but the number and extent of the deviations were influenced by the concentration and duration of the exposure. Abnormalities included pycnosis, "sticky" anaphase and telophase bridges with or without fragments, c-mitosis and inhibition of cell division. Chromosome and chromatid breakage with erosion and fragmentation were maximum at metaphase and anaphase four hours after treatment with 0.1 ppm oil concentration. Binucleate cells, micro-and macronuclei and some polyploidy appeared following recovery in -tap water. Spindle abnormalities were indicated by arrested meta-phases, multipolar anaphases and misdivision at anaphase. It is suggested that these chromosomal and spindle aberrations were induced by the carbon-carbon double bonds present in the unsaturated acids of the sunflower seed oil which enabled them to function as electron donors and to undergo such reactions as the addition of hydrogen, of water and of acids. / Science, Faculty of / Botany, Department of / Zoology, Department of / Graduate

Thesis (Ph. D.)--University of Michigan, 1927. / Thesis note on label mounted on p. 57. "Reprinted from the American Naturalist, vol. LX, January-February, 1926." "Literature cited": p. 77-81.

No description available.

Thesis (M.Ag.Sc. 1974) from the Dept. of Agronomy, University of Adelaide.

Thesis (PH. D) Johns Hopkins university. / Biographical note. Reprinted from Journal of experimental zoology, vol. VI, no. 4 Bibliographical foot notes.

The northwestern muskrat (Ondatra zibethicus spatulatus) is nowhere more abundant than in the delta of the Mackenzie River in northern Canada. An investigation was undertaken to assess the adjustments resident animals have made in order to inhabit a region more than one hundred miles inside the Arctic Circle. The rigours of the physical environment demand that these animals live in burrows rather than in lodges of vegetation, as in more southern areas. During summer the breeding pairs may occupy shallow temporary habitat which is not suitable for tenure during winter. These summer sites must be vacated before ice seals the lakes and prevents escape from a rapidly deteriorating environment. That all muskrats do not desert this temporary summer habitat was indicated by the fact that only half as many marked animals from such sites were encountered subsequently. It may be assumed that a depressed survival was the rule in such locations. Only deeper lakes with adequate submerged food plants constituted satisfactory wintering environment. Normal movement of muskrats in the Mackenzie delta is an average distance of about 300 yards in summer and 100 yards in winter. Winter activity is supported by an extensive system of feeding stations or "push-ups" constructed on the lake ice. These structures are a necessary part of the dally life of the individual muskrat because the dispersed nature of the food plants demands a relatively great radius of activity. The number of muskrats using each push-up varies from three to thirteen with an average of six. The relatively short period of open water in this latitude so shortens the breeding season that primiparous females probably produce only one litter of young their first year of life. However, they can, by maturing sexually at an earlier date their second year, produce two litters. Inasmuch as the late winter population is comprised of four yearlings to each adult female, the delay in breeding induced by the late removal of ice on the lakes and channels is significant In reducing the rate of population Increase. The restrictive effects of climate on breeding activity are compensated for by the birth of larger litters (8.3 young) and by a very satisfactory survival of these young to yearling status. Intolerance between adults is noted during the early part of the breeding season but does not persist during the rearing of the young. As a consequence there are few losses from depredations of adults upon young animals as has been reported in other areas. Densities of animals per unit area are low when compared with races of muskrats from other regions. In addition the size of the individual animal is small, and the majority do not survive long past their second year of life. These observations support the view that the Mackenzie delta provides marginal habitat for muskrats. It is suggested that physical factors induced by the severity of the climate represent the major influence limiting population growth. The fur industry is another significant drain on animal numbers but other factors appear to be less important. All mortality factors taken together, however, have suppressed or eliminated any tendency for muskrat numbers to fluctuate in a cyclic manner as has been reported by several authors for other parts of North America. Reference is made throughout the text to races of muskrats inhabiting more southern latitudes. / Science, Faculty of / Zoology, Department of / Graduate

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg in fulfilment of the requirements for the degree of Master of Science. Johannesburg, 2018 / The morphological variation between populations is shaped by adaptive responses to prevailing environmental conditions and/or not adaptive stochastic effects. Within-population variation is mainly related to age and sexual dimorphism, as well as temporal and spatial variation in environmental conditions. The aim of this study was to investigate patterns of variation in the skull, mandibles, and dentition in a population of the African four-striped mouse Rhabdomys dilectus chakae. Geometric morphometrics was used to assess the variation related to allometry and age, sexual dimorphism, and the inter-annual variation between specimens collected in different years (1975, and 1994-1997). A review of the literature on the application of geometric morphometrics to rodent morphological variation was conducted and landmark morphometrics were concluded to be the most appropriate methods for the skull and the mandible analyses, with a separate analysis using landmarks and semi-landmarks to analyse the variation of mandibular curves, and outline morphometrics with an Elliptic Fourier analysis of the upper molars. Images of the skull (ventral and lateral view at 5x magnification), mandible (at 6.8x magnification), and the three left upper molars (at 10.5x magnification) were captured using a stereoscopic microscope. Landmarks were digitized on the skull and mandible images, with semi-landmarks digitized on mandible images, and outlines were digitized on molars. Multivariate analysis of variance was used to analyse shape and size variation due to age, sex, and year of sampling and a multivariate regression was used to analyse allometry. A PCA was used to visualize shape variation, and boxplots of log-centroid size to visualize size variation between age classes, sexes, and years of sampling. Shape variation was significantly predicted by age and year of sampling, while size was significantly predicted by age, sex, and year of sampling. Size significantly contributed to shape variation, although size alone did not appear to explain much of the variation present. Most age-related variation in shape was due to differences between the first three age classes and age class IV, while size increased with increased age (i.e. growth). Males were larger than females although no sexual shape dimorphism was evident between sexes. Typical of species with male-male competition, Rhabdomys dilectus chakae demonstrated sexual size dimorphism; larger males have greater mating opportunities. Specimens from 1994 and 1997 had more variable shapes and were consistently smaller than those collected in 1975, 1995 and 1996, except for dentition where these latter specimens were smaller than those collected in 1994 and 1997. Annual variation in morphology may be a plastic response to prevailing local climatic conditions (i.e. rainfall and temperature), Masters Dissertation Candice Neves iv resulting in annual variation in diet, affecting the skull and dentition. Further studies should consider more populations in the species to assess the generalizability of the findings, particularly annual variation, and to consider spatial variation across the distribution of a population. / GR2019