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Title: Life history biology of the parasitic nematode Strongyloides ratti
Author: Gemmill, A. W.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1999
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Causes and consequences of plasticity in parasite life histories were investigated using a gastrointestinal nematode species, Strongyloides ratti, a natural parasite of rats. Empirical work focused on three putative instances of adaptive and non-adaptive plasticity in the life history of S. ratti: host-specificity, facultative sexuality, and immune-dependent maturation time. Host-specificity (the differential success of a parasite on alternative host types) represents (non-adaptive) plasticity in fitness and is commonly viewed as an unavoidable outcome of parasite specialisation - an intuitive conclusion that has rarely been questioned. While the lifetime reproductive success of two S. ratti lines was unaffected by host (rat) genotype, the frequency and timing of sampling was crucial in quantifying host-specificity accurately. Proximate processes generating the differential performance in S. ratti in rats and mice were then characterised and quantified. Reduced parasite fitness in mice resulted from lower parasite establishment, more rapid expulsion and suppressed fecundity. Differences in the efficacy of thymus-dependent (T-dependent) immunity between host species were insufficient to explain this variation in parasite fitness. Experimental natural selection and reciprocal fitness assays were used to discriminate between alternative models and host-specific specialisation. Selection failed to modify host-specificity suggesting either a lack of genetic variation among parasites or the action of unidentified factors underlying the different performance of S. ratti in rats and mice. The S. ratti life-cycle incorporates a facultative sexual phase and the frequency of sex depends on the strength of host acquired immunity. Immunisation of rats with infective larvae of other nematode species or with mammalian antigens reduced the reproductive success of parasites but only immunity acquired against S. ratti induced a facultative increase in the frequency of sexual reproduction indicating antigen-specificity of this plasticity.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available