Hoverflies (Diptera: Syrphidae) vary widely in their mimetic associations, comprising wasp-mimetic, bee-mimetic and non-mimetic species. Social wasp mimics are dominated by 'imperfect mimics' which outnumber their supposed models (Hymenoptera: Vespidae) by large factors. The purpose of this thesis is to determine to what degree Batesian mimicry can account for these paradoxes, and to test alternative hypotheses for the evolution of the yellow-and-black patterns. There is little evidence of an effect of wasp abundance on 'imperfect mimic' abundance across 23 years of trapping data, as predicted if mimics are protected from predators through their resemblance to wasps. The seasonal asynchrony and high abundance of 'imperfect mimics' relative to their models is also notable, as well as the possible significance of wasp predation on hoverflies. Predictions concerning the function of the colour patterns of 'imperfect mimics' are tested using the association between similarity to the model and flight agility (indirectly measured assuming a trade-off between reproductive potential and flight agility). There is no strong indication that mimetic protection is the primary function of the colour patterns, but the evidence concurs with an aposematic function, signalling to predators the unprofitability of attempting capture. These conclusions are tentatively supported by direct measures of flight agility, though the small differences among species are difficult to pick up. The data on reproductive morphology of hoverflies show considerable variation across species, especially in males. The existence of giant testes in some species suggests that methods of dealing with sperm competition in hoverflies are diverse and deserve further study. The high ratio of 'imperfect mimics' to both models and good wasp mimics is also partly explained by habitat disturbance; undisturbed habitats show significantly less 'imperfect mimics' as a proportion of the hoverfly population. Current relative abundance in the UK may therefore be very different to when the colour patterns evolved.

The seaweed fly, Coelopa frigida, lives in piles of rotting seaweed deposited on beaches by tides and winds. In all populations studied it is polymorphic for two gene arrangements on Chromosome I. A polymorphism at the alcohol dehydrogenase locus is strongly associated with this inversion and can be used to estimate karyotype frequencies. An extensive series of samples from natural populations has revealed a seasonal cycle in inversion frequencies but otherwise frequencies are remarkably constant both geographically and temporally. There is a consistent excess of heterokaryotypes in these samples. Three selective forces influencing inversion frequencies have been investigated. 1) An association between karyotype and development time, previously observed in the laboratory, has been demonstrated in conditions case to those in natural populations. 2) Viability differences between karyotypes have been examined. In natural populations there is some evidence that the excess of heterokaryotypes increases with larval density. In the laboratory heterokaryotypes are shown to have higher viability than either homokaryotype but the strong density dependence reported previously has not been observed. Viability differences are concentrated in the first two days of larval life and are probably related to the rate of supply of nutrients. 3) An association is demonstrated between karyotype and adult size - especially in males. Adult size is shown to correlate with longevity and fecundity of both sexes. Several experiments indicate that large males enjoy greater mating success than small males. The relationship between larval density, development time and adult size is described. The possibility that the effect of the inversion varies between populations or between alcohol dehydrogenase genotypes has also been investigated. A simulation has been used to study how these selective forces interact with one another, and with the changeable environment in which the flies live, and to examine the extent to which they can account for the observed karyotype frequencies.

Studies were undertaken to measure genetic toxicity at the molecular and cytogenetic levels of biological organisation in marine invertebrates and flatfish. The responses in the early life stages and adult life stages of marine invertebrates (Mytilus edulis and Platynereis dumerilii) were measured following exposures to the physical agent ultraviolet radiation (UVR) and representative compounds of the chemical group, polycyclic aromatic hydrocarbons (PAHs) in laboratory conditions. Also, the potential changes of toxicity of PAH contaminants caused by interactive effects with UVR were evaluated. In a collaborative study with researchers at the Centre for Environment, Fisheries and Aquaculture Science (CEFAS), genotoxic measurements were carried out in marine flounder (Platichthys flesus) which had been chronically exposed in vivo to PAHs administered via their food in controlled laboratory conditions. Significantly elevated levels of DNA damage were only observed in fish exposed to the highest PAH concentrations. Dose-dependent cytogenetic responses were observed in the early life stages of both of the invertebrate species investigated following exposure to UVR. However, statistically significant increases in chromosomal aberration induction and sister chromatid exchange (SCE) induction, and decreases in proliferation rate index (PRI) and normal development were only observed at UVR levels exceeding that of equivalent environmentally realistic conditions, when related to historical and predicted ozone levels in the south west of England. The interactive effects of UVR and PAHs indicated that the genotoxic potential of PAHs is increased when photoactivation takes place, measured by increases in genotoxic responses in both the early and adult life stages. Following a series of laboratory studies, a field study was conducted whereby indigenous populations of marine invertebrates {Mytilus edulis and Cerastoderma edule) were used as target organisms. Haemolymph samples were collected from the animals and tested for genotoxic and cytotoxic effects, employing assays validated in the earlier laboratory studies. Correlations between samples showing high levels of DNA damage measured with the comet assay and sites with high levels of heavy metals in the sediments and soft tissue of the animals were established. Finally, an attempt was made to evaluate the DNA repair capabilities of haemocytes collected from M.edulis, A series of in vitro exposures were carried out using hydrogen peroxide (H2O2) an oxidising agent, and methyl methane sulfonate (MMS) an alkylating agent to induce DNA damage. These were incubated with cytosine β-D-arabino furanoside (AraC), to establish whether these cells had the capacity to repair DNA damage induced by the model chemicals. The results showed that DNA damage induced by H2O2 required DNA polymerases for repair, whereas MMS-induced damage and repair did not appear to be affected by the presence of AraC. In conclusion, the data collated from the research undertaken for this project showed that UVR and PAHs are able to induce genotoxic lesions measurable at the cytogenetic level and whole organism levels in early life stages; and at the molecular and cellular levels in the adult stages. The assays employed appeared to be useful for identifying potential "hotspots" for genotoxic agents in the environment as indicated by the results of the field study, however, the endpoints measured are not contaminant-specific and provide little information about the type of contaminant or agent which might be present. Nonetheless, it has been shown here that comet assay is applicable to different marine species (including Cerastoderma edule and Platichthys flesus) and it is a potentially useful method for detecting DNA damage as well as DNA repair.

Thesis (M.S.)--University of Wisconsin--Madison, 1969. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 1995. / Vita. Includes bibliographical references (leaves [249]-286).

Thesis (Ph. D.)--University of Chicago, Committee on Evolutionary Biology, December 1999. / Includes bibliographical references. Also available on the Internet.

Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2009. / Full text also available online. Scroll down for electronic link.

Invertebrates influence primary productivity and nutrient cycling in ecosystems. They are also important links between producer and higher trophic levels. Despite their important role in terrestrial ecosystem function, invertebrates are frequently overlooked in ecological restorations. Thus, the objective of this research was to quantify how belowground macroinvertebrate ecosystem engineers and communities change over time following ecological restoration and examine whether the source of dominant plant species and the composition of non-dominant plant species influence aboveground macroinvertebrates community structure in restored prairie. A chronosequence design (space for time substitution) was used to determine the role of restoration age, plant community, and soil structure on the recovery of two belowground macroinvertebrate ecosystem engineers (Chapter 2). Ants and earthworms were sampled from cultivated fields, grasslands restored for 1-21 years, and native prairie. Earthworm abundance increased with time since cessation of cultivation, concomitant with prairie establishment. The abundance and biomass of ants were more related to the structure of restored plant communities than time since restoration. The dominance of exotic earthworms, and a generalist ant species in these restorations, coupled with their known capacity to alter soil properties and processes, may represent novel conditions for grassland development. The same chronosequence of agricultural fields, restored prairies, and prairies that were never cultivated was used to address the second objective of this research, which was to quantify how the belowground macroinvertebrate community composition changed in response to ecological restoration and whether the communities became representative of undisturbed (“target”) communities. Macroinvertebrate communities in the two remnant prairie sampled were distinct from restorations and continuouslycultivated fields. The macroinvertebrate communities in prairie that had never been cultivated were also distince from each other, indicating a “target” community is hard to define. Belowground macroinvertebrates changed in a trajectory that was not representative of either remnant prairie, but was representative of the an average of both remnant prairies. Thus, if you reconstruct prairie from cultivated soil conditions (“build it”), macroinvertebrates will colonize (“come”), but attaining a community representative of a specific target may require introduction from that target. Colonization of macroinvertebrates in restorations aboveground are most likely to be influenced by aspects of the plant community. A third objective of this research was to quantify whether variation in dominant species (cultivars vs. local ecotypes) and composition of subordinate species (local species pools) influence the composition of aboveground macroinvertebrates. Macronvertebrate abundance, richness, diversity, trophic groups and community composition in late summer did not vary between prairie restored with cultivar and local ecotypes of the dominant grasses. This was observed in two field experiments. The species pool treatment did influence the macroinvertebrate community, as one species pool had slightly higher morphospecies diversity and hymenopterans that the other two species pools. This was likely due to the presence of an ant-tended legume, Chamaecrista facsciculata Michx., in one species pool. Overall, this research demonstrates that time since the cessation of disturbance (cultivatation) and plant communities influence macroinvertebrate communities in restored prairie. Restored prairies in the Midwest are likely to be colonized by exotic earthworms and cosmopolitan ants. More research is needed to reveal how they influence ecosystem functioning.Belowground, macroinvertebrate communities may not represent restoration “targets” and these “targets” may be hard to define if remnants are rare or there is a high degree of spatial variation on the landscape. Variation in plant communities above ground appears to influence the structure of aboveground macroinvertebrate communities more than variation within dominant species. Whether this aboveground variation is reflected is reflected belowground deserves further investigation.

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