Variation and covariation in infectivity, virulence and immunodepression in the host–parasite associationGammarus pulex–Pomphorhynchus laevis

Abstract

Parasites often manipulate host immunity for their own benefit, either by exacerbating or suppressing the immune response and this may directly affect the expression of parasite virulence. However, genetic variation in immunodepression, which is a prerequisite to its evolution, and the relationship between immunodepression and virulence, have rarely been studied. Here, we investigated the variation among sibships of the acanthocephalan parasite, Pomphorhynchus laevis, in infecting and in immunodepressing its amphipod host, Gammarus pulex. We also assessed the covariation between infectivity, parasite-induced immune depression and host mortality (parasite virulence). We found that infectivity, the intensity of immunodepression and virulence were variable among parasite sibships. Infectivity and the level of immunodepression were not correlated across parasite sibships. Whereas infectivity was unrelated to host mortality, we found that gammarids that were exposed to the parasite sibships that immunodepressed their hosts the most survived better. This positive covariation between host survival and immunodepression suggests that gammarids exposed to the less immunodepressive parasites could suffer from damage imposed by a higher activity of the phenoloxidase.

A standardised protocol for measuring phenoloxidase and prophenoloxidase in the honey bee, Apis mellifera

“…The ratio of PO to ProPO activity in bees was found to be approximately 1 to 365 in these experiments, much greater than that recently seen in the amphipod Gammarus pulex (activity levels of ProPO found to be approximately 15 times greater than those of PO, Cornet et al, 2009a). However, in preliminary data for this study, and subsequent experiments, PO activity was found to be the more variable parameter compared to ProPO activity; the high variation in honey bee PO activity levels associated with seasonal and treatment effects could cause the ratio of PO to ProPO activity to drop as low as 1 in 50 in some cases (Laughton, 2008).…”

Infection with Wolbachia protects mosquitoes against Plasmodium‐induced mortality in a natural system

“…, 2010), Wolbachia downregulates the nonspecific arm of the mosquito immune system. There is increasing evidence that immune activation is costly in terms of both energetic resources (Moret & Schmid‐Hempel, 2000) and immunopathology (Sadd & Siva‐Jothy, 2006; Cornet et al. , 2009) and, as such, contributes to parasite virulence (Little et al.…”

“…Another possible tolerance mechanism may arise if, as shown in the pill bug Armadillium vulgare (Braquart-Varnier et al, 2008;Sicard et al, 2010), Wolbachia downregulates the nonspecific arm of the mosquito immune system. There is increasing evidence that immune activation is costly in terms of both energetic resources (Moret & Schmid-Hempel, 2000) and immunopathology (Sadd & Siva-Jothy, 2006;Cornet et al, 2009) and, as such, contributes to parasite virulence (Little et al, 2010). A downregulation of the immune system would result in higher parasite loads but in a lower per-parasite cost to the host (higher tolerance, Little et al, 2010).…”

Eco‐immunology and bioinvasion: revisiting the evolution of increased competitive ability hypotheses

“…PO is a general defence and nonself recognition system in arthropods that provides immunity against a large range of pathogens. Nonetheless, its activity leads to the production and release of cytotoxic molecules that generate immunopathologic costs (Cornet, Franceschi, Bollache, Rigaud, & Sorci, 2009). The lower PO activity found in invading wasps (Wilson-Rich & Starks, 2010) and gammarids (Cornet et al, 2010) can be analogous to the reduced investment in costly inflammatory response of vertebrates.…”