A hypothesis to explain host species differences in resistance to multi-host parasites

Mark Forbes,Julia Mlynarek

doi:10.4033/iee.2014.7.5.n

Abstract

Here, we offer a novel hypothesis to explain why some host species evolve resistance, whereas other related species remain susceptible to a shared parasite species. We first describe instances of single water mite species that are ectoparasitic on different species of host dragonflies, where the mites are killed by resistance mechanisms and have little to no fitness on some host species. This begs the question of why some host species are susceptible, whereas other host species are (nearly) completely resistant. Earlier logic based on parasites exploiting abundant host species at the cost of exploiting rare host species does not explain such instances well. Rather, a hypothesis based on closed populations of some host species being able to evolve parasite recognition is invoked. Parasite recognition is not expected to evolve in host species from more open populations with considerable gene flow across sites, only some sites of which have the parasite species present. The logic of this hypothesis can be explored with simulation models, whereas empirical tests could involve combined approaches using molecular genetics, population genetics, experimental infections and transplantation experiments.

Highlights

Many species of parasites exploit several to many host species for a given stage of their life cycle (Lajeunesse and Forbes 2002, Poulin 2007). These broad host species ranges are still the case even after cryptic species are uncovered by genetic barcoding, i.e., some of the cryptic species are generalists (Hebert et al 2004, Smith et al 2007)
In some parasite-host associations, host phylogeny is a main predictor of host species exploitation by parasite races or species, whereas in other associations, host ecology— temporal and spatial overlap between host species—appears to be an important determinant of host species use
Host species’ phylogeny, ecology, and physiology might all be determinants of specificity of host species use by parasite species, but the strengths of these determinants differ across different parasite-host associations

Summary

Introduction

Many species of parasites exploit several to many host species for a given stage of their life cycle (Lajeunesse and Forbes 2002, Poulin 2007). Researchers ought to study instances of strong differences in resistance between host species to single species of parasites. One possible determinant of such obvious differences in resistance to parasites is relative host species abundance.

Results

Conclusion