Analysis of the bacterial flora of Zygaena larvae from several colonies was made. Marked differences in midgut flora were consistently found in larvae from different colonies) even though the bacteria associated with the food plants were essentially the same. In all larvae certain bacteria on the food plant were eliminated in the midgut to produce the flora characteristic of that colony. The mechanism by which this selective inhibition occurred was investigated, and a system is described which produces in vitro the inhibition found in vivo. The significance of the bacterial flora of the larvae is discussed. A system for the aseptic rearing of Zygaena larvae is described, which may be adapted for other phytophagous insects, also a method for the fluorescent labelled antibody tracing of cellular antigens in insect tissues. During a population study of a colony of Zygaena filipendulae (L.) and Z. lonicerae (von Schev.) (Lepidoptera, 4ygaenidae) it was found that microbial diseases caused only a low percentage of mortality among the larvae. Results indicated that in years of high larval densities, food shortage would be a factor tending to limit population size. In 1967, both populations suffered heavy mortality as a result of parasitism by Telenomus (hymenoptera, Scelionidae). First report is made of a polyhedrosis virus infection of the family Aygaenidae.

A review is presented of the literature relating to the ability of fish to learn problems involving discrimination within a variety of sensory modalities, using a number of types of response. The literature concerning the functions of both optic tectum and forebrain is considered. Various experiments are described which demonstrate the ability of goldfish (Carassius auratus) to habituate to new situations, to form simple conditioned responses, an to perform increasingly complicated avoidance tasks.

RNA interference (RNAi) is a eukaryotic phenomenon where short double-stranded RNA molecules (dsRNAs) repress homologous sequences. In insects RNAi has been widely observed and has proved extremely useful as a reverse genetics tool to elucidate the function of newly identified genes, as well as showing potential as a novel insecticide. Unfortunately, however, not all insect species are equally susceptible to RNAi. This thesis explores whether persistence of dsRNA in insect hemolymph, uptake of dsRNA into insect tissue, or activation of RNAi genes could be limiting factors in RNAi experiments. Trials were conducted with the tobacco hornworm, Manduca sexta, a species in which experimental difficulty has been experienced with RNAi protocols and the German cockroach, Blattella germanica, which is known to be highly susceptible to experimental RNAi. In M. sexta larvae dsRNA disappeared rapidly from the hemolymph in vivo. By comparison, exogenous dsRNA persisted longer in the hemolymph of B. germanica adults. These findings lead me to propose that the rate of persistence of dsRNA in insect hemolymph may be a key factor in determining the susceptibility of insect species to RNAi. Despite such rapid breakdown of dsRNA in M. sexta larvae uptake of exogenous dsRNA into hemocytes, fat body and midgut could be detected by quantitative RT-PCR in vivo and was experimentally investigated in hemocytes in vivo and in vitro using fluorescently labelled dsRNA. Furthermore, quantitative-RT-PCR revealed that the expression of two M. sexta RNAi genes dicer-2 and argonaute-2 (partial sequences of which were isolated during this study) was specifically upregulated in response to injection with dsRNA.

A four year study investigated some soil-inhabiting pests which cause damage to sugar-beet seedlings. Sampling methods are discussed and a convenient and quick flotation technique for extracting arthropods from soil samples, and other methods, are described. Soil sampling sugar-beet fields in Spring, at many pest-infested sites, showed that blaniulid millipedes, pygmy beetle (Atomaria linearis) and onychiurid Collembola migrate from the subsoil and inter-row spaces and move progressively into the rows where they aggregate around sugar-beet seedling roots. 'Drilling-to-a-stand', with the concomitant wider seed spacing, sometimes increased numbers of millipedes and pygmy beetle per seedling root-zone, but never, onychiurid Collembola. Seedling roots at 9 in. spacing were usually damaged more than those from seed spaced at either 1 in. or 1.5 in. but the narrowest spacing sometimes improved seedling growth. Seedlings were smaller on plots receiving a pre-emergence herbicide but numbers of root-zone pests and damage was not affected. The damage to seedlings caused by millipedes is described in detail; it was also confirmed that Onychiurus spp. Collembola could kill seedlings in the laboratory and were generally the most common soil-inhabiting pest. Some factors which may affect damage by soil-inhabiting pests in the field and laboratory were reported. Timing of sowing could affect seedling survival; raw and pelleted seed was differentially attractive to some pests; soil compaction was sometimes beneficial. The biology and life-history of millipedes (Brachydesmus superus) and two common blaniulids: Blaniulus guttulatus and Boreoiulus tenuis was studied both in the field and in the laboratory. Two autumn surveys plotted the distribution of millipedes in the major sugar-beet growing areas in England. Some aspects of millipede behaviour were studied in the laboratory; soil temperature levels affected both their orientation and pattern of feeding behaviour; vertical and horizontal soil columns tested their reaction to soil moisture status. Studies on the effect of different insecticides showed that seed-treatments may be effective in the laboratory but their performance in the field, against millipedes, was inconsistent. Many insecticides, in seed or furrow formulation, killed pygmy beetle; the currently recommended insecticide, gamma-BHC, performed consistently well but was toxic to a mite predator of Onychiurus.

Sexual selection continues after copulation when the ejaculates from different males compete to achieve fertilization. Post-copulatory sexual selection is therefore a powerful evolutionary pressure, with seminal fluid emerging as an important factor. This thesis studies the role of seminal fluid in sexual selection in the polyandrous Red junglefowl, Gallus gallus. First, sperm Average Path Velocity (VAP) in vitro was higher over time when sperm were exposed to non-self, and particularly non-self related, seminal fluid. There was a tendency for sperm exposed to non-self seminal fluid to produce more hydrolysis points on the PVL membrane of the egg than sperm exposed to self seminal fluid. Second, males preferentially invested sperm in sexually novel females, by decreasing investment over successive copulations with the same female and increasing it again on encountering the new female. Seminal fluid volume allocation patterns mirror those of sperm. Seminal fluid protein allocation showed a status-specific pattern. While dominant males tended to allocate a constant amount of seminal fluid protein to successive copulations, subdominant males tended to increase their investment on the novel females. Third, I identified 1,141 proteins in the Red junglefowl seminal fluid, including proteins involved in immunity and antimicrobial defences, sperm maturation, metabolism, and fertilization. These proteins reveal a substantial contribution of blood plasma proteins that is conserved with humans. A comparison with the domestic fowl seminal fluid proteome, revealed qualitative and quantitative differences, likely associated with domestication and artificial selection. Fourth, by comparing the seminal fluid proteome of young and old males with fast and slow sperm velocity, I identified proteins associated with male reproductive ageing and sperm quality. This thesis shows that seminal fluid can play a potentially important role in sexual selection, and provides novel insights regarding male fertility and the molecular basis of reproductive divergence in seminal fluid proteins associated with domestication and artificial selection.

This thesis uses genealogical trees to identify, date, and quantify patterns of admixture between Neandertals and individual modern human populations, using a combination of high quality data and parametric methodology. Previous methods on this subject have either approximated features of trees, or inferred them indirectly. Here, genealogical trees are used directly to understand the admixture process between humans and Neandertals by extending a recently developed method named CEPHi: Coalescent Estimation of Population History. CEPHi uses recombinationally cold regions of the human genome to build genealogical trees specifying the relationships between individuals in two input populations (one Neandertal, one human), including estimated population size histories, split times, and coalescence and mutation times. Using CEPHi, a Neandertal-human population split time of ~712,000 years in the past is estimated, as well as uncovering loci introduced by Neandertal-human admixture, revealing distinct bimodal distributions of estimated coalescence times between non-African and Neandertal haplotypes. A Neandertal population history is inferred, from the time of their split with humans up to ~50,000 years ago (the fossil age), showing this archaic species to have suffered a bottleneck at this time, consistent with leaving Africa, followed by a further reduction to extinction. Contrasting African-Neandertal and Eurasian-Neandertal analyses are used to define admixture using genealogical trees, and test our procedures in CEPHi via coalescent-based simulations. This region-level definition of admixture is used to specify sets of introgressed coldspots across 13 modern human populations. These sets are compared between pairs of populations, revealing information about the possible timing of interactions between Neandertals and modern humans, and sharing of admixture events between human groups, especially with respect to the split time between European and Asian populations. Online sets of introgressed regions for each of the four continents in our dataset are provided: African, American, Asian, and European. Finally, in order to investigate the variation in time of contact between Neandertals and individual human populations, a novel method is described and implemented which dates admixture between individual human populations and Neandertals, using information from genealogical trees. Dates of admixture are estimated as ~50-60,000 years in the past in European populations, and ~80-90,000 years in the past in Asian populations, suggestive of potentially somewhat distinct histories between European and Asian populations. This method can be applied to date any set of introgressed regions, including those shared between particular populations, enabling a clearer picture of the joint evolutionary history of modern humans, Neandertals, and other archaic species.

No description available.

No description available.

No description available.

No description available.