Freshwater streams in the developed world are becoming increasingly dominated by treated wastewater. Continually discharged into most surface waters, these effluents contain a suite of bioactive man-made chemicals, including steroid and non-steroid oestrogens, which have been found to feminise male fish, skew sex ratios, and cause reproductive failure. However, the consequences of reproductive disruption remain poorly explored at the population level. This thesis was initiated to evaluate how oestrogenic contaminants might influence the population ecology of a common cyprinid, the roach (Rutilus rutilus). An investigation encompassing population structure, multigenerational exposure and the role of additional drivers of fish population dynamics was undertaken to contextualise the effects of oestrogenic effluents on wild fish populations. Population genetic analysis of UK roach found they exhibit moderately high levels of genetic diversity and significant intra-river genetic structure. Genetically differentiated local subpopulations indicate little interbreeding and limited gene flow, consistent with a typical metapopulation that has not been homogenised by restocking. Similarly, my thesis demonstrates no significant relationship between effluent exposure and Ne (effective population size) or genetic diversity of roach populations, albeit a 65% reduction in Ne is possible at highly polluted sites. River stretches contaminated with high levels of effluent can support breeding populations, which recruit successfully with minimal immigration from less contaminated sites. Multigenerational effects of effluent exposure on roach were also evaluated experimentally using reproductive success from breeding adults over three generations. Lifelong exposure to 100% treated effluent resulted in feminised phenotypes (ovarian cavities and intersex condition) in males but no observable effect on females. Additionally, despite gonadal disruption in males and effluent exposure of their mothers, I found no detrimental effect on their ability to compete with control fish. Instead, reproductive success was primarily determined by body size. A novel approach considering additional fish population drivers suggests that genetic diversity and species diversity decline in parallel with an increasing presence of disturbed land, when combined with geographical isolation. In conclusion, group assemblage and genetic structure of fish populations appears multi-causal and cannot be disaggregated, such that a single environmental characteristic can be shown to drive patterns of population success.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:646256 |
| Date | January 2014 |
| Creators | Nicol, Elizabeth |
| Contributors | Jobling, S.; Sumpter, J. |
| Publisher | Brunel University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://bura.brunel.ac.uk/handle/2438/10826 |
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