Highly potent host external immunity acts as a strong selective force enhancing rapid parasite virulence evolution

2017

Ecology and Evolution

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Sociobiology has revolutionized our understanding of interactions between organisms. Interactions may present a social dilemma where the interests of individual actors do not align with those of the group as a whole. Viewed through a sociobiological lens, nearly all interactions can be described regarding their costs and benefits, and a number of them then resemble a social dilemma. Numerous experimental systems, from bacteria to mammals, have been proposed as models for studying such dilemmas. Here, we make use of the external immune system of the red flour beetle, Tribolium castaneum, to investigate how the experimental duration can affect whether the external secretion comprises a social dilemma or not. Some beetles (secretors) produce a costly quinone‐rich external secretion that inhibits microbial growth in the surrounding environment, providing the secretors with direct personal benefits. However, as the antimicrobial secretion acts in the environment of the beetle, it is potentially also advantageous to other beetles (nonsecretors), who avoid the cost of producing the secretion. We test experimentally if the secretion qualifies as a public good. We find that in the short term, costly quinone secretion can be interpreted as a public good presenting a social dilemma where the presence of secretors increases the fitness of the group. In the long run, the benefit to the group of having more secretors vanishes and becomes detrimental to the group. Therefore, in such seminatural environmental conditions, it turns out that qualifying a trait as social can be a matter of timing.

Section: Methods and Experimental Designmentioning

confidence: 99%

Social dilemma in the external immune system of the red flour beetle? It is a matter of time

Gokhale

Traulsen

2017

Ecology and Evolution

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“…To avoid colony collapses here we used a fungus, Beauveria bassiana (B.b. ), which upon single exposure is affected by the external secretion of the beetles while in the long run becomes resistant and more virulent (Rafaluk et al, 2017). Here we chose a fungus spore concentration of 10 8 spores per gram of flour for the preparation of the spore-flour mixture (Rafaluk et al, 2017).…”

Section: Methods and Experimental Designmentioning

confidence: 99%

“…), which upon single exposure is affected by the external secretion of the beetles while in the long run becomes resistant and more virulent (Rafaluk et al, 2017). Here we chose a fungus spore concentration of 10 8 spores per gram of flour for the preparation of the spore-flour mixture (Rafaluk et al, 2017). As a stress control and to control for host-parasite interactions, we also introduced a treatment using heat killed spores of the fungus.…”

Section: Methods and Experimental Designmentioning

confidence: 99%

“…Quinones of interest auto-fluoresce with a peak at 245 and 246 nm. To fully capture the quinone secretion on a plate reader we took measures from 210 to 262 nm and calculated the area under curve (Joop et al, 2014; Rafaluk et al, 2017). As a conservative estimate all the individuals secreting more quinone than twice the baseline secretion were considered to be secretors, for that treatment.…”

Section: Methods and Experimental Designmentioning

confidence: 99%

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Social dilemma in the external immune system of the red flour beetle? It is a matter of time

Gokhale

Traulsen

2017

Preprint

Self Cite

Sociobiology has revolutionized our understanding of interactions between organisms. Interactions may present a social dilemma where the interests of individual actors do not align with those of the group as a whole. Viewed through a sociobiological lens, nearly all interactions can be described regarding their costs and benefits, and a number of them then resemble a social dilemma. Numerous experimental systems, from bacteria to mammals, have been proposed as models for studying such dilemmas.Here, we make use of the external immune system of the red flour beetle, Tribolium castaneum, to investigate how the experimental duration can affect whether the external secretion comprises a social dilemma or not. Some beetles (secretors) produce a costly quinone-rich external secretion that inhibits microbial growth in the surrounding environment, providing the secretors with direct personal benefits. However, as the antimicrobial secretion acts in the environment of the beetle, it is potentially also advantageous to other beetles (nonsecretors), who avoid the cost of producing the secretion. We test experimentally if the secretion qualifies as a public good. We find that in the short term, costly quinone secretion can be interpreted as a public good presenting a social dilemma where the presence of secretors increases the fitness of the group. In the long run, the benefit to the group of having more secretors vanishes and becomes detrimental to the group. Therefore, in such seminatural environmental conditions, it turns out that qualifying a trait as social can be a matter of timing. K E Y W O R D Spublic goods, social evolution, Tribolium castaneum

“…The beetle T. castaneum, which had evolved under conditions allowing for host-parasite coevolution with the fungal parasite B. bassiana [ 32 , 33 ] was the host for the experiments mentioned in our paper. During the evolution experiment [ 32 , 33 ], B. bassiana was present in the environment of the beetles, thereby, allowing for infection to occur naturally. We performed survival assays with the entomopathogenic bacteria Bacillus thuringiensis bv.…”

Section: Introductionmentioning

confidence: 99%

Cross-Resistance: A Consequence of Bi-partite Host-Parasite Coevolution

Biswas

Rafaluk‐Mohr

2018

Insects

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Host-parasite coevolution can influence interactions of the host and parasite with the wider ecological community. One way that this may manifest is in cross-resistance towards other parasites, which has been observed to occur in some host-parasite evolution experiments. In this paper, we test for cross-resistance towards Bacillus thuringiensis and Pseudomonas entomophila in the red flour beetle Tribolium castaneum, which was previously allowed to coevolve with the generalist entomopathogenic fungus Beauveria bassiana. We combine survival and gene expression assays upon infection to test for cross-resistance and underlying mechanisms. We show that larvae of T. castaneum that evolved with B. bassiana under coevolutionary conditions were positively cross-resistant to the bacterium B. thuringiensis, but not P. entomophila. Positive cross-resistance was mirrored at the gene expression level with markers that were representative of the oral route of infection being upregulated upon B. bassiana exposure. We find that positive cross-resistance towards B. thuringiensis evolved in T. castaneum as a consequence of its coevolutionary interactions with B. bassiana. This cross-resistance appears to be a consequence of resistance to oral toxicity. The fact that coevolution with B. bassiana results in resistance to B. thuringiensis, but not P. entomophila implies that B. thuringiensis and B. bassiana may share mechanisms of infection or toxicity not shared by P. entomophila. This supports previous suggestions that B. bassiana may possess Cry-like toxins, similar to those found in B. thuringiensis, which allow it to infect orally.