Experimental evolution of parasite life-history traits inStrongyloides ratti(Nematoda)

Abstract

Evolutionary ecology predicts that parasite life-history traits, including a parasite's survivorship and fecundity within a host, will evolve in response to selection and that their evolution will be constrained by trade-offs between traits. Here, we test these predictions using a nematode parasite of rats, Strongyloides ratti, as a model. We performed a selection experiment by passage of parasite progeny from either early in an infection ('fast' lines) or late in an infection ('slow' lines). We found that parasite fecundity responded to selection but that parasite survivorship did not. We found a trade-off mediated via conspecific density-dependent constraints; namely, that fast lines exhibit higher density-independent fecundity than slow lines, but fast lines suffered greater reduction in fecundity in the presence of density-dependent constraints than slow lines. We also found that slow lines both stimulate a higher level of IgG1, which is a marker for a Th2-type immune response, and show less of a reduction in fecundity in response to IgG1 levels than for fast lines. Our results confirm the general prediction that parasite life-history traits can evolve in response to selection and indicate that such evolutionary responses may have significant implications for the epidemiology of infectious disease.

Predators and Patterns of Within-Host Growth Can Mediate Both Among-Host Competition and Evolution of Transmission Potential of Parasites

“…However, in these highpredation lines, the bacterium evolved to produce fewer spores later during infection when compared to the low simulated predation treatment. This costly evolutionary response echoes previously developed theory (Anderson and May 1982;Kakehashi and Yoshinaga 1992;Lenski and May 1994;Ebert and Weisser 1997) and earlier experimental studies (nematode-rats: Paterson and Barber 2007;bacterium-Paramecia: Nidelet et al 2009). Thus, costly evolution of faster growth occurs in diverse host-parasite systems.…”

“…A lab-based experimental evolution study supported this prediction: the bacterium, but not the fungus, produced spores more rapidly but at lower maximal yield in selection lines mimicking higher predation rate. Therefore, the bacterium showed the capacity to evolve into the faster-schedule niche, but with a cost (see also Paterson and Barber 2007;Nidelet et al 2009). More broadly, this evolution result, coupled with the competition outcomes in model 3, shows how predators and life history of parasites can jointly shape the abundance, distribution, and evolution of parasites.…”

Selecting for fast and slow maturing worms

“…This effect of the drug industry may have alarming consequences, since epidemiological parameters like virulence, disease dynamics and host recovery rates are closely linked to parasite life histories (Anderson & May 1982;Frank 1996;Gandon et al 2001). A paper in the current issue of Proceedings B (Paterson & Barber 2007) provides new insights into how parasite life histories may evolve under selection regimes that simulate drug treatments.…”

Research Note. Occurrence of gastrointestinal helminths in commensal rodents from Tabasco, Mexico

“…Furthermore, three of the aforementioned species (H. polygyrus, S. ratti and T. crassicauda) have never before been reported in Mexico. Heligmosomoides polygyrus and S. ratti are two of the most commonly used para sites in laboratory experiments (Paterson & Barber, 2007;Reynolds et al, 2012). Trichosomoides crassicauda is specifi c for the urinary bladder of rats and its occurrence indicates that the feces were contaminated with urine.…”