The evolutionary ecology of host-specificity: experimental studies with Strongyloides ratti

Abstract

Factors constraining the evolution of host-specificity were investigated using a gastrointestinal parasitic nematode, Strongyloides ratti. S. ratti is a natural parasite of rats which can also reproduce, with decreased success, in laboratory mice. Observed host-specificity arose from lower establishment, reduced per capita fecundity and more rapid expulsion of parasites from mice relative to rats. Variation in the efficacy of thymus-dependent immunity between host species (rats and mice) was insufficient to explain the majority of the observed differences in parasite establishment and reproductive success. The role of natural selection in determining host-specificity was addressed using experimental selection followed by reciprocal fitness assays in both host species. Experimental selection failed to modify the host-specificity of S. ratti to any measurable degree, suggesting either a lack of genetic variation for this trait or the involvement of as yet unidentified factors underlying the differences in S. ratti fitness in rats and mice respectively. These results are discussed in relation to competing theoretical models of ecological specialization, host immunology and previous attempts to experimentally alter the host-specificity of parasitic nematodes.

Strongyloides myopotami in ctenomyid rodents: Transition from semi-aquatic to subterranean life cycle

“…Therefore, the possibility of colonising a new host declines with an increase of the phylogenetic distance among host species. Indeed, studies on host specificity of a related species, Strongyloides ratti, a natural parasite of rats (Rattus rattus), showed that it can complete its life-cycle in laboratory mice (Mus musculus), but with a decreased reproductive success, due to lower establishment rates, earlier expulsion of established parasites and reduced per capita fecundity in mice (Gemmill et al 2000). The authors failed to find the factors underlying the differences in S. ratti fitness among rats and mice, and no evidence for interactions between host and parasite genotypes has been found in later studies (Paterson 2005).…”

“…However, the dispersion of S. ratti to wild populations of mice seems unlikely, because there have been only two reports of Strongyloides spp. (one of them as S. ratti) in wild-caught mice since the late nineteenth century (Gemmill et al 2000).…”

Strongyloides ratti Infection Induces Expansion of Foxp3+ Regulatory T Cells That Interfere with Immune Response and Parasite Clearance in BALB/c Mice

“…Experimental infection of mice induces patent, but transient, infections that are resolved spontaneously within 2-4 wk and render the mice semiresistant to subsequent infections. Although mice, not being the natural host, display lower worm burden compared with the natural host, the rat, the overall kinetics of infection and immune response are comparable (27)(28)(29). S. ratti infection provokes a classical type 2 response in both species that is characterized by the induction of IL-13, IL-5, IL-3, and IL-10, as well as high titers of S. ratti-specific IgM and IgG1 (30,31).…”

Development and application of three-dimensional skin equivalents for the investigation of percutaneous worm invasion

“…The host range of S. ratti is in comparison to S. mansoni highly limited to a few host species (Brant and Loker, 2013;Gemmill et al, 2000). It is comprehensible that the capability to invade into the non-host skin preparations is reduced, since the surface structure and also the chemical attractants may be different.…”