The aim of the current study were two fold; Firstly to establish the mechanism and timing of occurrence of fertility parameters associated with the onset of puberty and to investigate the effects, mechanisms and mode of action of restricted energy intake on growth rate, and age at puberty. Secondly, to study the effects of mating at different intervals post-partum on early fertility parameters and to identify the fertility parameters affected by early remating in three breeds of rabbits - the Local Cameroonian, the Californian and the New Zealand. The effects of two energy levels of intake on the onset of puberty were investigated. The results showed that restricted energy intake had no effect on mating behaviour but that, a critical level of oestradiol 17? was necessary to render the pituitary sensitive to GnRH following mating. It also revealed that the effects of nutrition on fertility parameters at puberty were mediated through the body weights achieved. Both a critical concentration of oestradiol 17? and another non-ovarian factor, probably of nutritional origin may be necessary for ovulation to occur. Experiment 2 provided data for pre- and post-implantation losses at different ages in does fed one of the two test diets. The results showed that after 19 weeks of age and above 1.8 kg body weight, growth rate had no effect on the proportion of does mating or ovulating and that, as does grew older there was an increase in metabolic resistance to restricted feed intake, whereby energy partitioning could have been altered giving preference to reproduction. Dietary energy intake had a negligible effect on corpus luteal function as reflected by progesterone profiles. The results also suggest that, most of the losses occurring prior to implantation were probably incurred during the very early period following mating (1-4 days), and were more likely to be related to fertilising ability than progesterone concentration. In experiment 3, the effect of altering the remating interval on early fertility parameters was investigated. Ninety-six does of the Local Cameroonian breed and 48 New Zealand white does were tested for mating 1, 7, 14, 21, 28 and 35 days post-partum one hour after blood samples had been collected to be analysed for oestradiol 17?. Does were slaughtered on the day of mating to assess the number of follicles of diameter > 1 mm and 2 days post-mating to assess ovulation response and rate. Receptivity increased with day of testing for mating post-partum with the highest response on day 1 and the lowest at 21 days post-partum. No correlation existed between follicles (> 1 mm) and day of mating post-partum. (r=0.03). Serum oestradiol 17? concentrations were not significantly different (p>0.05) on any day of mating, although the concentrations tended to be higher on day 1 post-partum. There was a te The overall results of this study reveal that besides the inherent reproductive characteristics of the doe rabbit, poor management practices as well as the high environmental temperatures characteristic of the tropics, could be responsible for the poor reproductive efficiency of the doe rabbit in Cameroon.

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The present study investigated antibacterial peptides in rainbow trout. Oncorhynchus mykiss. The growth inhibition zone assay was optimised for use with fish bacterial pathogens. Magainin 1 was inactive against all bacteria tested while cecropins P1 and B were very efficient against all Gram negative fish pathogens. The A-layer of Aeromonas salmonicida had a protective effect against cecropins. Cecropin B was more potent and had a wider spectrum of activity than cecropin P1. Defensin HNP-2 was active against three Gram positive bacteria and one Gram negative bacterium. The most sensitive strain to cecropins, A. salmonicida MT004, was chosen as the test microorganism. Purification of antibacterial compounds from rainbow trout was optimised using solid-phase extraction followed by reverse-phase C8 HPLC. Five HPLC peaks purified from gut leucocyte culture supernatants contained inducible antibacterial molecules including a 2131Da-peptide. Five antibacterial HPLC peaks obtained from blood leucocyte culture supernatants contained inducible antibacterial compounds. The most potent weighed 2149g/mol. Its small size, high potency and rapid induction post-challenge would potentate its development as a therapeutic agent. Eight very potent antibacterial peptides weighing between 2500 and 8800g/mol were isolated from serum. The N-terminal sequences of three of them, weighing 2595, 7942 and 7931Da respectively were determined and they were named salmocidins 1, 2 and 3 respectively. The effect of different stimuli on their production was assessed by HPLC and indirect ELISA using a specific polyclonal antibody raised against salmocidin 1. Salmocidin 1 was particularly interesting (large peak on reverse-phase HPLC facilitates its isolation; potency against the test microorganism, small size therefore potentially cheap to synthesise chemically). Salmocidin 1 is a very interesting, novel antibacterial peptide that may provide a satisfactory alternative to antibiotics in fish farming and may find clinical.

(1) Zooplankton, containing 80% of their lipid as wax esters, were fed to young rainbow trout for up to 3 months without any obvious ill-effects. Although these fish absorbed 90% of the dietary lipid, triacylglycerols were by far the major lipid present in the tissue of the pyloric caeca. Freshwater rainbow trout, which do not encounter large quantities of wax esters in their natural diet, assimilated wax esters as efficiently as herring, a seawater species that has a natural diet of wax ester-rich zooplankton. The efficiency of wax ester absorption did not change over 9 weeks of feeding the wax ester-rich diet. It appears, therefore, that the ability to assimilate these lipids is inherent and widespread among fishes. (2) Electron microscopy showed that the general morphology of the pyloric caeca of rainbow trout fed wax esters and the visible steps of lipid absorption resemble those documented for the mammalian small intestine and its absorption of triacylglycerols. The distribution of lipid in the pyloric caeca supports the hypothesis that this tissue is involved in lipid absorption and metabolism in fish fed wax esters. The trout could digest and absorb the zooplankton lipid within 18h, which is consistent with their being capable of deriving much of their carbon from dietary wax esters. (3) Hexadecanol, glucose and aspartate were all incorporated into tissue triacylglycerols and there was evidence for a link between hexadecanol oxidation and glycerol phosphate synthesis. The rates of triacylglycerol formation from the water-soluble and the hydrophobic substrates were similar. The water-soluble substrates (except glycerol) had a higher rate of CO2 production. There was no clear-cut effect of species or diet on the rate of substrate metabolism. (4) There was no evidence of fatty acid- or fatty alcohol-binding proteins in fish analogous to the fatty acid-binding protein of rat. The 'binding' of fatty alcohol, and to a lesser extent fatty acid, to high molecular constituent(s) of liver and caecal cytosols may be due largely to non-specific interactions with lipid. (5) A soluble NAD+-dependent ethanol dehydrogenase purified from trout caeca did not readily oxidize hexadecanol, in contrast to the crude cytosolic fraction. The greatest rate of hexadecanol oxidation in the pyloric caeca and liver of trout was achieved by an NAD+-dependent microsomal system. The microsomal fraction also contained an NAD+- dependent acetaldehyde dehydrogenase which may be involved in the further oxidation of aldehyde to acid. Feeding fish wax ester-rich zooplankton had no obvious effect on the activity of these enzyme systems. (6) The metabolic activity of the tissue slices and subcellular fractions were much less than the capacity of the intact fish to dispose of dietary wax ester. There are several possible reasons for this discrepancy, including the problems of studying enzyme catalysis in heterogeneous systems.

In this thesis, I explore how an individual’s environment, or the environment of its mother, affects its reproductive life-history characteristics (age at maturity, size at maturity, offspring size, offspring number). I attempt to explain observed responses using adaptive reasoning and/or mathematical modelling. I find that mean egg size decreases with increasing clutch size in <i>Daphnia, </i>and explore possible causes of this using a mathematical model. This pattern could be an adaptive response, if larger offspring have greater fitness advantages in food-limited environments. However, such a pattern can also result from a minimum viable egg size that is similar to the optimal egg size. I also empirically test the fitness effects of hatching from a small or large egg in <i>Daphnia. I </i>find that offspring from food-limited mothers are larger, but that they mature later, produce less offspring per clutch, do not produce larger offspring and produce fewer offspring per unit time. I find that the nematode parasites <i>Strongyloides ratti </i>and <i>Nippostrongylus brasiliensis </i>mature at different rates depending on the efficacy of the host immune response, but that differences are species-dependent. In addition, female <i>N. brasiliensis </i>suffer decreased fecundity at higher densities, but only in hosts with fully-functioning immune systems; in hosts with no thymus-based immune system, there is no density-dependent fecundity effect. This suggests that the density-dependent effects often observed in parasitic nematodes are mediated by the host immune system. This thesis reminds us that small differences in an individual’s surroundings, or even its mother’s surroundings, can profoundly affect when, how, and how successfully an animal reproduces. Often, these effects can be explained using adaptive reasoning, and/or mathematical modelling. When and how an animal reproduces is certain to have consequences for its fitness. Implications and future research directions are also discussed.

Gene homologues were identified by carrying out BLAST searches of the chicken genome and EST databases. Following identification, an expression profile of each gene was obtained using RT-PCR, Northern and <i>in situ </i>hybridisation analyses carried out on embryos at stages of embryonic development which PGC specification; PGC migration to the gonads and PGC development in the gonads occurred. Analyses focused on the genes <i>bruno, germ cell-less, oct4, mago nashi, nanog, nanos, piwi, pumilio </i>and <i>staufen </i>and aimed to determine (1) whether gene expression was comparable to the expression of homologues in other species, (2) whether the gene was expressed in areas known to contain PGCs, (3) whether the gene was expressed specifically in PGCs and (4) whether the gene could have a potential role in PGC development. Of the genes chosen to be investigated, homologues of <i>bruno, germ cell-less, mago nashi, piwi, pumilio </i>and <i>staufen </i>were identified in the genome and in EST databases. No <i>nanos </i>homologues were identified by this method. Homologues of <i>oct4 </i>and <i>nanog </i>were identified by Dr B.Pain who provided sequence data for both genes. analyses showed that the expression of all the genes were comparable to expression patterns in other species. <i>Nanog </i>and <i>oct4 </i>were expressed in a pattern that indicated germ cell specific expression. This led to additional <i>in situ</i> hybridisation, PGC transfer and qPCR analyses at later stages of development. These data showed how expression of <i>oct4 </i>and <i>nanog </i>changed in relation to (1) the loss of PGC motility in males and females and (2) the onset of meiosis in females. Of the remaining genes, <i>germ cell-less </i>and <i>piwi </i>were detected specifically in adult testes, whereas the rest were detected in areas of the embryo known to contain PGCs. However, the gene expression was not PGC specific.

TPLSM is the approach used to address how asymmetric cell divisions might take place in the retina. Asymmetric cell division is a mechanism thought to be involved in generating neuronal diversity from a homogeneous progenitor population, and may be mediated by the orientation of progenitor cell divisions. 3D reconstructions of the developing zebrafish retina were analysed for orientation of cell division. Contrary to currently proposed models for vertebrate asymmetric divisions, apico-basally oriented cell divisions, perpendicular to the ventricular surface, are not found to occur in the zebrafish retina during the formation of postmitotic neurons. However, a shift in the orientation of cell division from central-peripheral to circumferential orientations occurs within the plane of the ventricular surface at a time when neuronal cells are differentiating. The shift from central-peripheral to circumferential divisions is absent or delayed in the <i>sonic you (syu)</i> mutant, which lacks retinal ganglion cell neurons. This delay correlates with a delay in neuronal differentiation, suggesting that the circumferential orientations of division may represent asymmetric, neuron-generating cell divisions. <i>In vivo</i> imaging also shows that mitotic cells, found in the apical side of the neuroephithelium, retain a process connected to the opposite basal surface, and that this process can be inherited asymmetrically by one daughter cell. Although this may also a play a role in asymmetric cell division, it does not correlate with a specific orientation of division. It may be important for the radial migration of newborn neurons to the appropriate layer of the retina. After neuronal differentiation, tangential migration of cells and cell death may be required to maintain regularity in newly-formed neuronal cell mosaics. The <i>in vivo</i> behaviour of amacrine cells in early development was studied using TPLSM. Amacrine cell death, correlated with short distances between cells, is shown to occur in early retinal development, although evidence for tangential cell migration is not found. It is plausible that apoptosis, thought to be a rare event in the zebrafish retina, is in fact required for the formation of regular cell mosaics by the removal of incompatible cells from a mosaic by short-range interactions with other cells in the mosaic.

Infertility is a major issue in both human and animal medicine with a great economic impact on reproduction. In order to better understand the common causes of infertility it is necessary to understand the basic physiology underlying the complex process of folliculogenesis and luteogenesis (Campbell et al., 2003). The lack of extensive understanding of the factors involved in regulating follicular and oocyte maturation has resulted in the slow process of developing in vitro systems for the study of folliculogenesis (Campbell et al., 2004). However, domestic ruminants represent a valuable in vivo model system for the study of the endocrine and local mechanisms regulating follicular development not only in ruminants but also in humans (Campbell et al., 2003) and have thus been extensively used in reproduction research. Improved understanding of the basic cellular mechanisms of ovarian physiology may improve biotechnology strategies in livestock reproduction and enhance fertility protocols for endangered species. Similarly, a better understanding of these reproductive processes could lead to innovative strategies to improve reproductive health in women.

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No description available.