Previous studies at the Rowett Institute showed that novel branched-chain fatty acids are present (up to 15%) in the adipose tissue triglycerides of sheep fed on diets containing a high content of a carbohydrate-rich cereal, such as barley. Rumen bacterial fermentation of this carbohydrate produces considerable amounts of propionate which apparently exceeds the animals' hepatic capacity to utilise it for gluconeogenesis or oxidation. For these processes propionate must be converted to succinate via methylmalonate by a vitamin B12-dependent enzyme. It was postulated that, in cereal-fed sheep, the methylmalonate which accumulates is incorporated into fatty acids synthesised de novo, thereby giving rise to branched-chain components. In the present work the above observations were extended and the results and conclusions are summarised below. 1. Lipids of kidney, liver and brain obtained from barley-fed sheep contained 6.7%, 4.3% and 0.7% respectively of branched-chain fatty acids. The carcass lipids of a neonatal lamb, born to a ewe which had been fed on barley throughout pregnancy also contained small amounts (0.6%) of these acids. 2. A comparison of the hepatic capacities of barley-fed sheep and grass-fed sheep to oxidise propionate in vitro revealed that liver of barley-fed sheep had the greater oxidative capacity. Similarly, it was shown that the livers of barley-fed sheep had a greater ability to activate and to oxidise methylmalonic acid. 3. Whereas methylmalonyl CoA behaved as a classical competitive inhibitor towards fatty acid synthatase prepared from adipose tissue of grass-fed sheep and from chicken liver, it did not do so towards the synthetase from the adipose tissue of barley-fed sheep. This non-classical inhibition was associated with the concurrent utilisation of methylmalonyl CoA for synthesis of branched-chain fatty acids. 4. The incorporation of [2-14C]-methylmalonic acid and [2-14c]-methylmalonyl CoA into monomethyl branched-chain fatty acids was demonstrated. Some of these (novel) acids were presumptively identified by capillary column gas chromatography. 5. In other, complementary, studies it was found that the liver lipids of a wild baboon contained very small proportions of branched-chain acids, apparently derived from methylmalonate. The proportions were increased in vitamin B12-depleted animals, especially following the administration of a vitamin B12 analogue which was antagonistic to vitamin B12 in its metabolic effects.

Invasion by non-native species has the potential to change native biodiversity, community structure, food webs and interactions between species.. Small scale manipUlative experiments :using sessile organisms have shown that increasing biodiversity reduces community susceptibility to invasion by non-native species. However, large scale observational studies have shown that some ofthe most diverse systems are the most invaded. The search fora generalised mechanism that may make a resident community resistant to invasion by a non-native species has proven difficUlt and has provided contrasting resUlts. Small scale experiments have been criticised for their dinllnptive spatial scale and -rdatively homogeneous environmental conditions. _ The contrasting results between the experimental and observational studies may be due to the heterogeneous nature ofmost environments which iilllY promote invasion as well as coexistence. In this thesis I study the relationship between invasion and competition in heterogeneous en'ir0nments using the North-East Asian amphipod Caprella mutica. Caprellids have been shown to live on marine sessile species such as, algae, hydroids, tunicates, mussels, bryozoans and sponges which attach to a hard substratum and form '. . erect structures that project into the wat~r column. Species-rich epifaunal comm.unities . can create a structurally diverse habitat. In choice experiments using different structural patches and structure types in the laboratory, there was no effect ofthe number of different types ofstructures in a patch on the number of C. mutica attached to a patch, but structure type was critically important. Caprella mutica preferred the filament.ous structures long t¢and short turf .over mussel mimics. In field experiments, densities were 7 times greater than the laboratory experiments.. There were twice as many caprellids on the structurally heterogeneous patches than on the structurally homogeneous patches. However, invasion patterns in the field did follow the same structure type as the laboratory experiments. Intraspecific competition appeared to be stronger on the homogeneous patches, whereas there were more refuges and microhabitats on the heterogeneous patches and this may have reduced the aggressive interactions between conspecifics. Artificial and live habitats were placed together in laboratory experiments and there was .t'. no difference in the number of caprellids attached to the artificial and live habitats. Lack ofdifferences between live biota and the artificial mimics showed that C. mutica habitat choice is most likely due to the physical characteristics ofthe habitat. Furthermore, choice oftype ofstructure did not differ betWeen the artificial and live patches. I In competition experiments between C. mutica and two native cap~ellids Caprella linearis and Pseudoprotella.phasma, C. mutica successfully displaced both species from homogeneous artificial habitat patches after 24 hours. Patches that had a refuge attached reduced the number of C. linearis being displaced but only when C. mutica was at a low density. Further experiments, using 3 different levels of structural heterogeneity with C. linearis .and C. mutica, showed that the two species could occupy the structurally heterogeneous patches at similar densities after the 24 hour experimenta~ period. On structurally homogeneous patches C. mutica significantly displaced C. linearis. Aggressive interactions were likely to have been more intense on the homogeneous than structurally heterogeneous patches and this study suggests that C. mutica displaces C. linearis through agonistic interactions. The same processes that reduced intraspecific competition in the first set ofexperiments also promoted coexistence between the two ecologically similar species. Consequently, structurally diverse habitats have the potential to promote invasion while at the same time reducing the impact of an invader on native species. Kelp communities consisting ofLaminaria hyperborea and Saccharina latissima in close proximity to known populations of C. mutica were surveyed and showed that C. mutica did disperse to the kelp communities but was not found on any ofthe kelp plants in the upper zone of the kelp bed. This study was limited to only sampling kelp plants to a depth of 1 to 2 m on spring tides and it is possible that C. mutica may inhabit kelp ' . plants that are deeper. However, laborat~ experiments showed Carcinus maenas predated on C. mutica and may provide biotic resistance to benthic emjronments from 'the invasion by C. mutica. Even at small spatial scales where environmental conditions were similar for both the laboratory and field experiments, the probability of invasion cannot be predicted ' reliably from aggregate community 'measures such as species richness (analogous to the number ofdifferent types ofstructures). Individual characteristics ofthe invading ,' species and positive'associations with structure types, even at small spatial scales, may increase the probability ofinvasion regardless of species richness. Thus, invasion by C. mutica is likely if an appropriate structure type is prese.nt and the success ofinvasion increases with an increasing richness of structure-forming epibiota. For native fauna, which have a similar ecological requirement to the invader, structural heterogeneity appears to reduce the impact ofthe invading species. Habitat heterogeneity may be essential for co-existence between a superior and inferior competitor, as structurally complex habitats offer a variety of different microhabitats and niches. The invasibility of a community, therefore, depends on the diversity and composition of the community being invaded, and the invasive potential of a species depends not only on the community properties, but also on the characteristics of the invader.

Fish exhibit a great variability in reproductive strategies. A particular mating system reported for some species of fish is the lek system. Studies on spawning behaviour of cod (Gadus, morhua) - a closely related species to haddock - have shown that the mating characteristics are consistent with lekking, meaning that cod are particularly vulnerable to disturbance by fishing on their spawning grounds. In this study the spawning behaviour of haddock, was examined and the prerequisites of lekking system were:'observed. Visual and acoustic displays ensured a clear area around a dominant male excluding less vigorous males and unripe females. Larger dominant males performed the solitary display for longer periods than smaller males, more during nights than days. Repeated female intrusions into the male's territory led to courtship and provided evidence that haddock mating is under female's control. Direct observations and DNA analysis demonstrated the existence of alternative male mating strategies. The ventral mount occurred generally outside the male territory. The acoustic repertoire of haddock, both during and outside spawning was described: sound unit structures and call duration were different and provided evidence of speci~s-specificsounds emitted by spawning males. The knocks emitted by each male during the solitary display had a constant waveform that differed from the knocks produced by the other individuals. Female and juvenile sounds were described for the first time. A simple mechanical model showed that a double pulsed sound waveform, could be obtained from two oscillators linked by a viscous-elastic spring, having opposite directions. A quadrupole motion of the haddock swimbladder was suggested. Detailed information about the haddock acoustic repertoire allowed us to detect for the first time haddock spawning grounds in the field (off Norway) by means of passive acoustic monitoring. Key words: haddock, lekking, fish sounds, wild spawning sounds.

Schistosomes cause human schistosomiasis, a parasitic disease infecting over 200 million people throughout the tropical and subtropical world. The parasite’s indirect life cycle requires a freshwater snail intermediate host, and its transmission dynamics is influenced by snail population dynamics. Subsequently, a thorough understanding of these population dynamics is important to our understanding of the epidemiology of schistosomiasis. With this is mind, this study investigated the processes underlying population dynamics of two snail intermediate hosts; <i>Bulinus forskalii</i> and the closely related <i>B. camerunensis.</i> Molecular markers provide powerful tools with which to address ecological questions and a suite of eleven polymorphic microsatellite loci, isolated and characterized from <i>B. forskalii </i>DNA, facilitated investigation of the mating system, structure and dynamics of <i>B. forskalii </i>and <i>B. camerunensis </i>populations from Cameroon. Microsatellite mutations detected during the course of a <i>B. forskalii</i> breeding experiment enabled estimation of the rate and mode of mutation of these markers. Mating system plays an important role in determining population structure and genetic analyses of laboratory-bred parent-offspring <i>B. forskalii,</i> as well as population genetic surveys of <i>B. forskalii </i>and <i>B. camerunensis</i>, identified this snail as a preferential selfer. The population genetic analyses of spatial and temporal data further suggested a high level of gene flow maintains genetic diversity within populations. The counteracting, eroding effects of genetic drift appear to be more important in driving genetic differentiation in the highly dynamic <i>B. forskalii</i> populations, compared with the relatively stable <i>B. camerunensis </i>ones. Both macrogeographic ecological and climatic parameters and microgeographic non-climatic factors influence <i>B. forskalii</i> population genetic structure. This study demonstrates the power of molecular markers, providing novel insight into factors determining the population structure and dynamics of two schistosome intermediate hosts. From this, a better understanding of the co-evolution of snail-schistosome interactions improves our knowledge of the epidemiology of human schistosomiasis.

No description available.

No description available.

After unilateral injury to the frons of adult locusts, their orientation to a lamp was unaffected for two hours. From 2-4 hours they turned the injured side away from a lamp. From 24 hours to five days they turned the injured side towards it; after that the injured side was turned away again. The amount of injury did not affect the response appreciably. Fifth instar nymphs gave the same results until they moulted, when normality was restored. In the absence of injury, nociceptive thresholds for various parts of the body were similar. The sensitivity of some parts (frons and abdomen) tested by a behavioural method after injury varied with time like the orientation behaviour. Electrophysiological experiments on the normal and injured abdomen also gave corresponding results. A subcuticular plexus of multipolar neurones is found in many parts of the locust body, with dendrites penetrating the endocuticle. The nymphs have a similar system and so do cockroaches. Dipteran and Lepidopteran larvae have a different, subepidermal system. A wound in the locust integument is closed and covered by new cuticle after five days. Axons apparently arising from new subcuticular neurones join the nervous system at that time.

The possibility that isolation or 'distress' calling in newborn rodents can be used to screen for anxiolytic activity was explored. The effects of a wide range of drugs that influence the benzodiazepine / GABA receptor complex, serotonergic, noradrenergic, dopaminergic and cholinergic transmitter systems on ultrasonic calling were systematically assessed, in 5-6 day old mouse pups, under controlled temperature conditions. Benzodiazepine agonists reliably decreased ultrasonic calling whereas inverse agonists increased it. The benzodiazepine antagonists, which had no significant influences <i>per se</i> on this measure, blocked the effects of both direct and inverse benzodiazepine agonists on ultrasonic calling. GABA agonists reduced ultrasonic calling although GABA antagonists had no significant effects on this measure. These antagonists did, however, block the effects of the agonist muscimol. Exposure of mouse pups to PTZ increased the number of calls. The action of PTZ was blocked by the benzodiazepine antagonist, Ro 15-1788. Three out of four serotonin agonists tested in these studies increased the number of ultrasonic calls, while the antagonists of serotonin suppressed such production. These effects on ultrasonic calls appear mediated by the 5-HT receptor, as the actions of some agonists are reliably blocked by specific antagonists. Tests with noradrenaline antagonists (<i>sensu</i> Carlson, 1986) (except AMPT) decreased ultrasonic calling. Apomorphine and sulpiride respectively increased and decreased the number of ultrasonic calls. With drugs acting via all receptors, changes in core body temperature and performance on the inclined plane test were routinely observed to identify possible indirect actions. Increases and decreases in calling generally appeared independent of thermoregulatory or sedative actions of drugs. It was concluded that ultrasonic calling can be used to quickly and accurately assess some classes of drugs for their anxiolytic or anxiogenic properties. Other experiments examined nest building and the behaviour of reproductive female mice after treatment with chlorpromazine, d-amphetamine or morphine sulphate. These preliminary data suggested that sedative drugs have major impacts on nest building and other activities, but additional studies have to be conducted to determine whether other tests based on the mother-infant bond will prove to be of utility in the study of psychoactive drugs.

No description available.

No description available.