Abstract
Immune responses are costly, causing trade-offs between defense and other host life history traits. Aphids present a special system to explore the costs associated with immune activation since they are missing several humoral and cellular mechanisms thought important for microbial resistance, and it is unknown whether they have alternative, novel immune responses to deal with microbial threat. Here we expose pea aphids to an array of heat-killed natural pathogens, which should stimulate immune responses without pathogen virulence, and measure changes in life-history traits. We find significant reduction in lifetime fecundity upon exposure to two fungal pathogens, but not to two bacterial pathogens. This finding complements recent genomic and immunological studies indicating that pea aphids are missing mechanisms important for bacterial resistance, which may have important implications for how aphids interact with their beneficial bacterial symbionts. In general, recent exploration of the immune systems of non-model invertebrates has called into question the generality of our current picture of insect immunity. Our data highlight that taking an ecological approach and measuring life-history traits to a broad array of pathogens provides valuable information that can complement traditional approaches.
Highlights
Invertebrates rely on innate immune mechanisms for protection against diverse parasitic organisms
We find significant reduction in lifetime fecundity upon exposure to two fungal pathogens, but not to two bacterial pathogens
This finding complements recent genomic and immunological studies indicating that pea aphids are missing mechanisms important for bacterial resistance, which may have important implications for how aphids interact with their beneficial bacterial symbionts
Summary
Invertebrates rely on innate immune mechanisms for protection against diverse parasitic organisms. Our current model of insect innate immunity relies heavily on knowledge from relatively few model organisms (e.g., Drosophila melanogaster (Lemaitre and Hoffmann 2007), Anopheles gambiae (Christophides et al 2004), Tribolium castaneum (Zou et al 2007)). The immune systems of some insects, differ from these models of innate immunity (Evans et al 2006; Smith et al 2011a,b), questioning the generality of our current picture of insect immunity. Assays of pea aphid (Acyrthosiphon pisum) immunity, using both genomic and experimental approaches, have found a reduced complement of conventional immune mechanisms. Pea aphids lack many presumably critical a 2013 The Authors.
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