Differential water mite parasitism, phenoloxidase activity, and resistance to mites are unrelated across pairs of related damselfly species.

Julia J Mlynarek,Mark R Forbes,Laura Nagel,Arne Iserbyt

doi:10.1371/journal.pone.0115539

Julia J Mlynarek, Mark R Forbes + Show 2 more

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https://doi.org/10.1371/journal.pone.0115539

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Abstract

Related host species often demonstrate differences in prevalence and/or intensity of infection by particular parasite species, as well as different levels of resistance to those parasites. The mechanisms underlying this interspecific variation in parasitism and resistance expression are not well understood. Surprisingly, few researchers have assessed relations between actual levels of parasitism and resistance to parasites seen in nature across multiple host species. The main goal of this study was to determine whether interspecific variation in resistance against ectoparasitic larval water mites either was predictive of interspecific variation in parasitism for ten closely related species of damselflies (grouped into five “species pairs”), or was predicted by interspecific variation in a commonly used measure of innate immunity (total Phenoloxidase or potential PO activity). Two of five species pairs had interspecific differences in proportions of individuals resisting larval Arrenurus water mites, only one of five species pairs had species differences in prevalence of larval Arrenurus water mites, and another two of five species pairs showed species differences in mean PO activity. Within the two species pairs where species differed in proportion of individuals resisting mites the species with the higher proportion did not have correspondingly higher PO activity levels. Furthermore, the proportion of individuals resisting mites mirrored prevalence of parasitism in only one species pair. There was no interspecific variation in median intensity of mite infestation within any species pair. We conclude that a species’ relative ability to resist particular parasites does not explain interspecific variation in parasitism within species pairs and that neither resistance nor parasitism is reflected by interspecific variation in total PO or potential PO activity.

Highlights

Explaining interspecific variation in parasitism among related host species has been one of the main goals of evolutionary parasitology [1]
We examined interspecific variation in prevalence and intensity of mite parasitism in relation to the proportion of individuals resisting Arrenurus water mites in ten species of coenagrionid damselflies
Prevalence of Arrenurus parasitism varied from 4% (1–10%, 95% Clopper-Pearson confidence interval) in A. moesta to 52% (42–62%, 95% Clopper-Pearson CI) in E. vesperum (Fig. 2A)

Summary

Introduction

Explaining interspecific variation in parasitism among related host species has been one of the main goals of evolutionary parasitology [1]. Comparing distantly related species can be difficult because of uncontrolled differences in environmental factors and actual identity and numbers of parasites exploiting the host species. In some taxonomic groups, variation in parasitism can occur among related host species even when ecological variables like habitat use and parasite species exploiting hosts are controlled [2]. Ecological and evolutionary factors such as geographical range, phylogeny or coevolution can explain differences in parasitism between host species [3], but unexplained variation often remains. One important research gap is the extent of tolerance and resistance between related host species to shared parasites [4]. A first look at this problem would be to compare levels of resistance to real parasites with respect to levels of parasitism and host defences, as done recently by Vogelweith et al [5]

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