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Exposure to bacterial signals does not alter pea aphids' survival upon a second challenge or investment in production of winged offspring.

ter Braak B, Laughton AM, Altincicek B, Parker BJ, Gerardo NM - PLoS ONE (2013)

Bottom Line: Immune priming was not altered by the presence of facultative, beneficial symbionts in the aphids.To test this, we monitored the ratio of winged to unwinged offspring produced by adult mothers of a single clone that had been exposed to bacterial immune elicitors, to live E. coli infections or to no challenge.We found no correlation between immune challenge and winged offspring production, suggesting that this mechanism of defense, which functions upon exposure to fungal pathogens, is not central to aphid responses to bacterial infections.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Emory University, Atlanta, Georgia, USA.

ABSTRACT
Pea aphids have an obligate nutritional symbiosis with the bacteria Buchneraaphidicola and frequently also harbor one or more facultative symbionts. Aphids are also susceptible to bacterial pathogen infections, and it has been suggested that aphids have a limited immune response towards such pathogen infections compared to other, more well-studied insects. However, aphids do possess at least some of the genes known to be involved in bacterial immune responses in other insects, and immune-competent hemocytes. One possibility is that immune priming with microbial elicitors could stimulate immune protection against subsequent bacterial infections, as has been observed in several other insect systems. To address this hypothesis we challenged aphids with bacterial immune elicitors twenty-four hours prior to live bacterial pathogen infections and then compared their survival rates to aphids that were not pre-exposed to bacterial signals. Using two aphid genotypes, we found no evidence for immune protection conferred by immune priming during infections with either Serratia marcescens or with Escherichia coli. Immune priming was not altered by the presence of facultative, beneficial symbionts in the aphids. In the absence of inducible immune protection, aphids may allocate energy towards other defense traits, including production of offspring with wings that could escape deteriorating conditions. To test this, we monitored the ratio of winged to unwinged offspring produced by adult mothers of a single clone that had been exposed to bacterial immune elicitors, to live E. coli infections or to no challenge. We found no correlation between immune challenge and winged offspring production, suggesting that this mechanism of defense, which functions upon exposure to fungal pathogens, is not central to aphid responses to bacterial infections.

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Aphid survival in relation to pre-exposure with bacterial elicitors and subsequent challenge with S. marcescens.A) B) In Experiment 1, while S. marcescens reduced aphid survival (pathogen-infected treatments are dotted, uninfected treatments are solid), the interaction between pre-exposure to bacterial elicitors (pre-exposed treatments are red, unprimed treatments are black) and subsequent challenge with live S. marcescens was not significant. A) Experiment 1, aphid genotype 5A0. B) Experiment 1, aphid genotype LSR1. C) In follow-up Experiment 2, giving all aphids (line 5AR) a subsequent challenge with live S. marcescens, pre-exposure did not impact survival. D) In follow-up Experiment 3, giving all aphids (genotype LSR1) a subsequent challenge with live S. marcescens, pre-exposure did not impact survival.
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pone-0073600-g001: Aphid survival in relation to pre-exposure with bacterial elicitors and subsequent challenge with S. marcescens.A) B) In Experiment 1, while S. marcescens reduced aphid survival (pathogen-infected treatments are dotted, uninfected treatments are solid), the interaction between pre-exposure to bacterial elicitors (pre-exposed treatments are red, unprimed treatments are black) and subsequent challenge with live S. marcescens was not significant. A) Experiment 1, aphid genotype 5A0. B) Experiment 1, aphid genotype LSR1. C) In follow-up Experiment 2, giving all aphids (line 5AR) a subsequent challenge with live S. marcescens, pre-exposure did not impact survival. D) In follow-up Experiment 3, giving all aphids (genotype LSR1) a subsequent challenge with live S. marcescens, pre-exposure did not impact survival.

Mentions: For Experiment 1 (Figure 1A, B), the minimal model indicated a marginally non-significant interaction between aphid genotype, pre-exposure, and infection treatment upon second challenge (p = 0.05), which is reflected by the somewhat different responses of the two aphid genotypes (5A0, LSR1) to pre-exposure and subsequent live bacterial challenge (Figure 1A,B). Upon second challenge with live bacteria, 5A0 aphids appear to have similar survival curves regardless of pre-exposure treatment (Figure 1A), whereas LSR1 aphids had slightly increased survival if they were pre-exposed to bacterial signals (Figure 1B). There was also a significant two-way interaction between genotype and pre-exposure treatment (p = 0.01), which may reflect the considerable natural variation in aphid responses to challenge, as has been shown previously [27]. Of importance here, regardless of whether the three-way interaction was retained in the model, the two way interaction between pre-exposure treatment and infection treatment upon second challenge was not significant (p > 0.09), which indicates that pre-exposure did not provide protection upon subsequent challenge with live bacteria. Experiment 2 (Figure 1C) and Experiment 3 (Figure 1D), with larger samples sizes and simpler, monofactorial designs, indicated no impact of pre-exposure on survival after subsequent live bacterial infections for either 5AR (Experiment 2, p = 0.28) or for LSR1 (Experiment 3, p = 0.27) aphids.


Exposure to bacterial signals does not alter pea aphids' survival upon a second challenge or investment in production of winged offspring.

ter Braak B, Laughton AM, Altincicek B, Parker BJ, Gerardo NM - PLoS ONE (2013)

Aphid survival in relation to pre-exposure with bacterial elicitors and subsequent challenge with S. marcescens.A) B) In Experiment 1, while S. marcescens reduced aphid survival (pathogen-infected treatments are dotted, uninfected treatments are solid), the interaction between pre-exposure to bacterial elicitors (pre-exposed treatments are red, unprimed treatments are black) and subsequent challenge with live S. marcescens was not significant. A) Experiment 1, aphid genotype 5A0. B) Experiment 1, aphid genotype LSR1. C) In follow-up Experiment 2, giving all aphids (line 5AR) a subsequent challenge with live S. marcescens, pre-exposure did not impact survival. D) In follow-up Experiment 3, giving all aphids (genotype LSR1) a subsequent challenge with live S. marcescens, pre-exposure did not impact survival.
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3756975&req=5

pone-0073600-g001: Aphid survival in relation to pre-exposure with bacterial elicitors and subsequent challenge with S. marcescens.A) B) In Experiment 1, while S. marcescens reduced aphid survival (pathogen-infected treatments are dotted, uninfected treatments are solid), the interaction between pre-exposure to bacterial elicitors (pre-exposed treatments are red, unprimed treatments are black) and subsequent challenge with live S. marcescens was not significant. A) Experiment 1, aphid genotype 5A0. B) Experiment 1, aphid genotype LSR1. C) In follow-up Experiment 2, giving all aphids (line 5AR) a subsequent challenge with live S. marcescens, pre-exposure did not impact survival. D) In follow-up Experiment 3, giving all aphids (genotype LSR1) a subsequent challenge with live S. marcescens, pre-exposure did not impact survival.
Mentions: For Experiment 1 (Figure 1A, B), the minimal model indicated a marginally non-significant interaction between aphid genotype, pre-exposure, and infection treatment upon second challenge (p = 0.05), which is reflected by the somewhat different responses of the two aphid genotypes (5A0, LSR1) to pre-exposure and subsequent live bacterial challenge (Figure 1A,B). Upon second challenge with live bacteria, 5A0 aphids appear to have similar survival curves regardless of pre-exposure treatment (Figure 1A), whereas LSR1 aphids had slightly increased survival if they were pre-exposed to bacterial signals (Figure 1B). There was also a significant two-way interaction between genotype and pre-exposure treatment (p = 0.01), which may reflect the considerable natural variation in aphid responses to challenge, as has been shown previously [27]. Of importance here, regardless of whether the three-way interaction was retained in the model, the two way interaction between pre-exposure treatment and infection treatment upon second challenge was not significant (p > 0.09), which indicates that pre-exposure did not provide protection upon subsequent challenge with live bacteria. Experiment 2 (Figure 1C) and Experiment 3 (Figure 1D), with larger samples sizes and simpler, monofactorial designs, indicated no impact of pre-exposure on survival after subsequent live bacterial infections for either 5AR (Experiment 2, p = 0.28) or for LSR1 (Experiment 3, p = 0.27) aphids.

Bottom Line: Immune priming was not altered by the presence of facultative, beneficial symbionts in the aphids.To test this, we monitored the ratio of winged to unwinged offspring produced by adult mothers of a single clone that had been exposed to bacterial immune elicitors, to live E. coli infections or to no challenge.We found no correlation between immune challenge and winged offspring production, suggesting that this mechanism of defense, which functions upon exposure to fungal pathogens, is not central to aphid responses to bacterial infections.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Emory University, Atlanta, Georgia, USA.

ABSTRACT
Pea aphids have an obligate nutritional symbiosis with the bacteria Buchneraaphidicola and frequently also harbor one or more facultative symbionts. Aphids are also susceptible to bacterial pathogen infections, and it has been suggested that aphids have a limited immune response towards such pathogen infections compared to other, more well-studied insects. However, aphids do possess at least some of the genes known to be involved in bacterial immune responses in other insects, and immune-competent hemocytes. One possibility is that immune priming with microbial elicitors could stimulate immune protection against subsequent bacterial infections, as has been observed in several other insect systems. To address this hypothesis we challenged aphids with bacterial immune elicitors twenty-four hours prior to live bacterial pathogen infections and then compared their survival rates to aphids that were not pre-exposed to bacterial signals. Using two aphid genotypes, we found no evidence for immune protection conferred by immune priming during infections with either Serratia marcescens or with Escherichia coli. Immune priming was not altered by the presence of facultative, beneficial symbionts in the aphids. In the absence of inducible immune protection, aphids may allocate energy towards other defense traits, including production of offspring with wings that could escape deteriorating conditions. To test this, we monitored the ratio of winged to unwinged offspring produced by adult mothers of a single clone that had been exposed to bacterial immune elicitors, to live E. coli infections or to no challenge. We found no correlation between immune challenge and winged offspring production, suggesting that this mechanism of defense, which functions upon exposure to fungal pathogens, is not central to aphid responses to bacterial infections.

Show MeSH
Related in: MedlinePlus