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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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Impact of challenge on offspring production.Mothers exposed to bacteria and to bacteria elicitors did not produce more winged offspring than unexposed mothers. Young adult females were not stabbed (control) or were stabbed with needles dipped in PBS (sterile stab), a heat-killed bacterial solution or a solution of live E. coli (live bacteria). Includes all offspring produced within 9 days of challenge. Error bars = s.e.m.
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pone-0073600-g003: Impact of challenge on offspring production.Mothers exposed to bacteria and to bacteria elicitors did not produce more winged offspring than unexposed mothers. Young adult females were not stabbed (control) or were stabbed with needles dipped in PBS (sterile stab), a heat-killed bacterial solution or a solution of live E. coli (live bacteria). Includes all offspring produced within 9 days of challenge. Error bars = s.e.m.

Mentions: We found that aphids of genotype LSR1, which readily produce winged aphids upon exposure to aphid alarm pheromone and crowing conditions (data not shown), did not increase production of winged offspring in response to exposure to either bacterial signals or to live E. coli pathogen infection. While 75% of control aphids had at least one winged offspring, only 37% of sterile stabbed aphids, 33% of aphids stabbed with heat killed bacteria, and 16% of aphids stabbed with live bacteria produced any winged offspring. Statistical analysis of the average proportion of winged versus unwinged offspring across all 9 days indicated no statistical differences between treatments (Figure 3, F3,30 = 1.12, p = 0.36). We also found no effect of treatment within any of the shorter windows of reproduction (days 1 to 3: F3,28 = 1.47, p = 0.24; days 4 to 6: F3,28 = 0.81, p = 0.50; days 7 to 9: F3,24 = 0.63, p = 0.54).


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)

Impact of challenge on offspring production.Mothers exposed to bacteria and to bacteria elicitors did not produce more winged offspring than unexposed mothers. Young adult females were not stabbed (control) or were stabbed with needles dipped in PBS (sterile stab), a heat-killed bacterial solution or a solution of live E. coli (live bacteria). Includes all offspring produced within 9 days of challenge. Error bars = s.e.m.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0073600-g003: Impact of challenge on offspring production.Mothers exposed to bacteria and to bacteria elicitors did not produce more winged offspring than unexposed mothers. Young adult females were not stabbed (control) or were stabbed with needles dipped in PBS (sterile stab), a heat-killed bacterial solution or a solution of live E. coli (live bacteria). Includes all offspring produced within 9 days of challenge. Error bars = s.e.m.
Mentions: We found that aphids of genotype LSR1, which readily produce winged aphids upon exposure to aphid alarm pheromone and crowing conditions (data not shown), did not increase production of winged offspring in response to exposure to either bacterial signals or to live E. coli pathogen infection. While 75% of control aphids had at least one winged offspring, only 37% of sterile stabbed aphids, 33% of aphids stabbed with heat killed bacteria, and 16% of aphids stabbed with live bacteria produced any winged offspring. Statistical analysis of the average proportion of winged versus unwinged offspring across all 9 days indicated no statistical differences between treatments (Figure 3, F3,30 = 1.12, p = 0.36). We also found no effect of treatment within any of the shorter windows of reproduction (days 1 to 3: F3,28 = 1.47, p = 0.24; days 4 to 6: F3,28 = 0.81, p = 0.50; days 7 to 9: F3,24 = 0.63, p = 0.54).

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