Interactive effects between diet and genotypes of host and pathogen define the severity of infection

Abstract

Host resistance and parasite virulence are influenced by multiple interacting factors in complex natural communities. Yet, these interactive effects are seldom studied concurrently, resulting in poor understanding of host-pathogen-environment dynamics. Here, we investigated how the level of opportunist pathogen virulence, strength of host immunity and the host condition manipulated via diet affect the survival of wood tiger moth Parasemia plantaginis (Arctidae). Larvae from “low cuticular melanin” and “high cuticular melanin” (considered as low and high pathogen resistance, respectively) selection lines were infected with moderately and highly virulent bacteria strains of Serratia marcescens, while simultaneously manipulating host diet (with or without antibacterial compounds). We measured host survival and food preference before and after infection to test whether the larvae “self-medicate” by choosing an anti-infection diet (Plantago major, i.e., plantain leaf) over lettuce (Lactuca sativa). “High melanin” larvae were more resistant than “low melanin” larvae to the less virulent strain that had slower growth and colonization rate compared with the more virulent strain. Cuticular melanin did not enhance survival when the larvae were infected with the highly virulent strain. Anti-infection diet enhanced survival of the “high melanin” but not the “low melanin” hosts. Survival was dependent on family origin even within the melanin selection lines. Despite the intrinsic preference for lettuce, no evidence of self-medication was found. These results demonstrate that the relative benefit of host cuticular melanin depends on both diet and pathogen virulence: plantain diet only boosted the immunity of already resistant “high melanin” hosts, and cuticular melanin increased host survival only when infected with moderately virulent pathogen. Moreover, there was considerable variation in host survival between families within both melanin lines suggesting genetic basis for resistance. These results indicate that although melanin is an important predictor of insect immunity, its effect on disease outcomes greatly depends on other interacting factors.

Evolutionary constraints of warning signals: A genetic trade-off between the efficacy of larval and adult warning coloration can maintain variation in signal expression

“…; Zhang et al. ) favors more melanic coloration with less conspicuous, and smaller sized, bright patterns. In addition, the strength and direction of selection on the warning signal traits can vary both spatially (Lindstedt et al.…”

“…The magnitude of the trade-off between larval and female warning signal efficiency can be strongly dependent on the spatial and temporal variation in the direction and strength of selection. Previous studies have shown that warning coloration of larvae and adults of A. plantaginis are under multiple selection pressures, as predation favors an increase in size and conspicuousness of brightly colored pattern elements (Lindstedt et al 2008(Lindstedt et al , 2011Nokelainen et al 2012) while thermoregulation Hegna et al 2013) and defense against pathogens (Friman et al 2009;Zhang et al 2012) favors more melanic coloration with less conspicuous, and smaller sized, bright patterns. In addition, the strength and direction of selection on the warning signal traits can vary both spatially (Lindstedt et al 2011;Nokelainen et al 2014;Gordon et al 2015) and seasonally ) in nature.…”

Appearance before performance? Nutritional constraints on life‐history traits, but not warning signal expression in aposematic moths

“…Based on previous studies, we can assume that in environments of high predation pressure, directional selection by predators should favour larger (Hegna, Nokelainen, Hegna, & Mappes, 2013;Lindstedt et al, 2008) and more salient (Lindstedt et al, 2011;Nokelainen, Hegna, Reudler, Lindstedt, & Mappes, 2012) warning signals in both the larval and adult stages of A. plantaginis and thus by default, less melanization surrounding them. However, in colder habitats (Hegna et al, 2013;Lindstedt et al, 2009), under higher risk of bacterial infections (Friman, Lindstedt, Hiltunen, Laakso, & Mappes, 2009;Zhang, Friman, Laakso, & Mappes, 2012), and under higher abundances of naïve predators (Lindstedt et al, 2008;Mappes, Kokko, Ojala, & Lindström, 2014), more melanic (i.e. more cryptic) genotypes should have an advantage.…”

Impact of the Glucosinolate Sinigrin on Bacterial Communities in <i>Pieris rapae</i>

“…Studies investigating resilience in insect midguts have shown that these communities are able to return to native community structure once removing perturbation factors such as antibiotics or high fat concentrations [17] [32]. In this study, the perturbation factor was not removed and yet the sinigrin 9.0 mg/ml treatment group showed no significant difference from the control treatment group.…”