My current work involves assessing the impact of effluents, and the endocrine disrupting chemicals (EDCs) they contain, on fish populations. Effluent exposure has been linked to a range of health effects in fish, including feminisation of male fish, genotoxicity, reduced fecundity and alterations in gene expression. A high proportion of male roach are 'feminised' to varying degrees in many lowland rivers in the United Kingdom. However, little is known of the potential consequences of their long-term presence in the environment on the size and/or genetic diversity of fish populations. The aim of the current project, funded by Natural Environment Research Council (NERC), is to determine whether the proportion of (estrogenic) effluent in rivers affects effective population sizes and the genetic diversity of roach (Rutilus rutilus) populations, as well as the probability that the population has undergone a historical population bottleneck. Effective population size is related to the number of reproducing individuals and is important for the long-term maintenance of genetic diversity. We are using a suite of 20 DNA microsatellites to genotype roach populations contemporary within the UK from sites with a range of levels of effluent contamination. We are also assessing the effects of maternal exposure to an estrogenic effluent on breeding success and responsiveness to estrogens.
I am also involved in a range of projects that use DNA microsatellites to understand "normal" breeding structures and population dynamics. We have used zebrafish (Danio rerio) to investigate the effects of EDCs of reproductive dominance. We found that exposure to ethinylestradiol (EE2), a component of the female contraceptive pill alters breeding dynamics in both males and females. I am also currently involved on projects involving guppies and sticklebacks.
My previous work research formed part of a larger collaborative research programme - Endocrine Disruption in Catchments (EDCAT). Roach has been used extensively for assessing the impacts of endocrine disrupting chemicals on wild fish. This project aimed to determine the relative reproductive success of these feminised males in comparison to more 'normal' males. This question was addressed using breeding studies using wild roach. Other members of the consortium have established groups of roach, containing both feminised and normal males, in large aquarium tanks. I developed a suite of polymorphic microsatellite loci that can be used to assign parentage (Hamilton et al. 2007). We found a significant impact of intersex on the reproductive success of male roach.
Trypanosome diversity and evolution
Prior to working in Exeter I did a PhD and a subsequent 8-month postdoctoral position in Bristol University as part of the Trypanosomiasis Research Group. Trypanosomes are highly successful parasites that live in the blood of vertebrates, and are transmitted by a wide range of invertebrate vectors, including tsetse flies, triatomine bugs and leeches. Several species are of considerable medical (Trypanosoma brucei and Trypanosoma cruzi) and veterinary importance (e.g. a range of tsetse fly-transmitted species in Africa). This work addressed some unresolved questions about the early evolution of trypanosomes, in particular whether trypanosomes had a single, or multiple origins and what gave rise to them. We have also investigated trypanosome diversity in largely unexplored geographical regions, such as Australia – which led to the discovery of several new species. Surprisingly, we also revealed unexpected diversity of well-studied trypanosomes that are transmitted by tsetse flies in Africa, including a species closely related to T. brucei. In order to facilitate studies of trypanosome diversity, we developed a high throughput DNA-based technique (Fluorescent Fragment Length Barcoding, FFLB) for identification of trypanosomes in tsetse flies, in collaboration with Emily Adams at Royal Tropical Institute, KIT Biomedical Research, Amsterdam, and Wendy Gibson at Bristol University. This technique has greatly improved accuracy of identification of African and South American trypanosomes (e.g. strains of T. cruzi) and led to discovery of strains which are potentially pathogenic. I am currently involved in a project exploring the diversity of trypanosomes in British bat with Fiona Matthews, Marta Teixeira and Jamie Stevens.
Hamilton, P.B., E. Nicol, E.S. De-Bastos, R.J. Williams, J.P. Sumpter, S. Jobling, J.R. Stevens and C.R. Tyler (2014) Populations of a cyprinid fish are self-sustaining despite widespread feminization of males. BMC Biology, 12: 1.
Harris, C.A.*, Hamilton, P.B.*, Runnalls, T.J., Jobling, S., Vinciotti, V., Henshaw, A., Hodgson, D., Coe, T.S., Tyler, C.R., Sumpter, J.P. (2011) The Consequences of Feminisation in Breeding Groups of Wild Fish (* joint first authorship). Environmental Health Perspectives 119: 306-311.
Hamilton, P. B. and Tyler, C. (2008) Identification of microsatellite loci for parentage analysis in roach Rutilus rutilus and 8 other cyprinids by cross-species amplification, and a novel test for detecting hybrids between roach and other cyprinids. Molecular Ecology Resources 8, 462-465.
Hamilton, P.B., Lewis M. D., Cruickshank, C., Gaunt, M. W., Yeo, M., Llewellyn, M. S., Valente S.A., Maia da Silva, F., Stevens, J.R., Miles, M.A., Teixeira, M.M.G. (2011) Identification and lineage genotyping of South American trypanosomes using fluorescent fragment length barcoding. Infection, Genetics and Evolution 11: 44–51.
Hamilton, P.B., Gibson, W.C., Stevens, J.R. (2007) Patterns of co-evolution between trypanosomes and their hosts deduced from ribosomal RNA and protein-coding gene phylogenies Molecular Phylogenetics and Evolution 43 (1):15-25.
Hamilton, P.B., Stevens, J.R., Gidley, J., Holz, P., Gibson, W.C. (2005) A new lineage of trypanosomes from Australian vertebrates and evidence of transmission by terrestrial bloodsucking leeches (Haemadipsidae). International Journal for Parasitology 35: 431-443.
Hamilton, P.B., Stevens, J.R., Gaunt, M.W., Gidley, J., Gibson, W.C. (2004) Trypanosomes are monophyletic: evidence from genes for glyceraldehyde phosphate dehydrogenase and small subunit ribosomal RNA International Journal for Parasitology 34 (12): 1393-1404.
Hamilton, P.B., Stevens, J.R., Cooke, B., Boag, B., Holz, P., Gibson, W.C. (2005) The inadvertent introduction into Australia of Trypanosoma nabiasi, the trypanosome of the European rabbit (Oryctolagus cuniculus), and its potential for biocontrol Molecular Ecology 14 (10): 3167-3176.
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