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|Title: ||The effects of the natural vertebrate steroid 17β-oestradiol and the xeno-biotic vertebrate oestrogen receptor agonist bisphenol-A on reproduction in selected temperate freshwater gastropods: the potential for (neuro-) endocrine disruption|
|Authors: ||Benstead, Rachel Samantha|
|Advisors: ||Routledge, E|
|Publication Date: ||2010|
|Publisher: ||Brunel University Institute for the Environment PhD Theses|
|Abstract: ||Evidence of feminising effects, including additional or enlarged female organs, have been reported in the (sub)-tropical freshwater prosobranch Marisa cornuarietis exposed to vertebrate estrogen receptor agonists. The primary symptom is an increase in the number of eggs laid, but this is only observed when exposure occurs at relatively low temperatures. This research project exposed temperate freshwater prosobranchs and a pulmonate to 17β-oestradiol (10-200 ngL-l, nominal) in an outdoor mesocosm subject to natural seasons to determine whether similar effects occur in European native temperate freshwater gastropods. Laboratory exposures to 17β-oestradiol (1-100 ngL-l, nominal) and Bisphenol-A (0.2-20 ngL-l, nominal) were also carried out over a range of different temperatures and photoperiods to simulate natural seasons.
In the mesocosm exposures, significant increases in reproduction were measured in Viviparus viviparus, Bithynia tentaculata and, if the mortality rate was not significantly increased, Planorbarius corneus. It was observed that increases only occurred after the onset of autumn. In the laboratory, the oviposition rate in P. corneus was constant at 20oC with a 16h photoperiod, but declined significantly at 15oC with a 12h photoperiod, except at 100 ngL-l 17β-oestradiol, when the rate remained constant. There were no similar effects from Bisphenol-A exposure. Small increases in reproduction were observed in all the prosobranch exposures to both compounds, but the interpretation of the data was confounded by several factors (test chemical degradation, high mortality rates and parasitized organisms) and there were no significant differences. In conclusion, there were indications that all of the assessed species were capable of increased reproduction, and in P. corneus this appears to be a perpetuation of summer oviposition rates in autumnal conditions. The consequences of this effect in annual semelparous pulmonates may not be detrimental at the population level, but the long-term fitness of iteroparous prosobranchs that practice ‘restrained reproduction’ in early breeding seasons may be adversely affected.|
|Description: ||This thesis was submitted for the degree of
Doctor of Philosophy and awarded by Brunel University, 2010.|
|Sponsorship: ||The Environment Agency|
|Appears in Collections:||Institute for the Environment Theses|
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