Aphid-encoded variability in susceptibility to a parasitoid
© Martinez et al.; licensee BioMed Central Ltd. 2014
Received: 28 March 2014
Accepted: 27 May 2014
Published: 10 June 2014
Many animals exhibit variation in resistance to specific natural enemies. Such variation may be encoded in their genomes or derived from infection with protective symbionts. The pea aphid, Acyrthosiphon pisum, for example, exhibits tremendous variation in susceptibility to a common natural enemy, the parasitic wasp Aphidius ervi. Pea aphids are often infected with the heritable bacterial symbiont, Hamiltonella defensa, which confers partial to complete resistance against this parasitoid depending on bacterial strain and associated bacteriophages. That previous studies found that pea aphids without H. defensa (or other symbionts) were generally susceptible to parasitism, together with observations of a limited encapsulation response, suggested that pea aphids largely rely on infection with H. defensa for protection against parasitoids. However, the limited number of uninfected clones previously examined, and our recent report of two symbiont-free resistant clones, led us to explicitly examine aphid-encoded variability in resistance to parasitoids.
After rigorous screening for known and unknown symbionts, and microsatellite genotyping to confirm clonal identity, we conducted parasitism assays using fifteen clonal pea aphid lines. We recovered significant variability in aphid-encoded resistance, with variation levels comparable to that contributed by H. defensa. Because resistance can be costly, we also measured aphid longevity and cumulative fecundity of the most and least resistant aphid lines under permissive conditions, but found no trade-offs between higher resistance and these fitness parameters.
These results indicate that pea aphid resistance to A. ervi is more complex than previously appreciated, and that aphids employ multiple tactics to aid in their defense. While we did not detect a tradeoff, these may become apparent under stressful conditions or when resistant and susceptible aphids are in direct competition. Understanding sources and amounts of variation in resistance to natural enemies is necessary to understand the ecological and evolutionary dynamics of antagonistic interactions, such as the potential for coevolution, but also for the successful management of pest populations through biological control.
KeywordsResistance Trade-off Symbiont Selection Fecundity Immunity
Insects and other animals face attack from a wide range of natural enemies which place strong selective pressures on the development, acquisition, and maintenance of resistance [1–10]. Intraspecific variation in resistance to natural enemies has been documented in many organisms and can stem from factors encoded in the host’s genome or those acquired from microbial associates [11–16]. Such variation is important for adaptation via natural selection, can promote the evolution of virulence in natural enemies, and drive host-enemy coevolutionary dynamics [13, 17]. Resistance, however, may also be expected to carry costs as resources allocated to the defense are unavailable for other functions , such that resistance may result in decreased fitness under enemy-free conditions [19–24]. Furthermore, selection for host resistance can reduce enemy prevalence or encourage increased virulence, which in turn, can result in negative frequency-dependent selection against the now potentially costly, resistant phenotypes [11, 25, 26]. Variability in resistance may also be maintained by fluctuations in enemy pressure, variation in enemy virulence, host-enemy specificity, and mediating environmental factors [12, 27–31]. Thus, quantifying variation and costs, and properly attributing the sources of variation in resistance to natural enemies, are often required to understand the ecological and evolutionary dynamics associated with antagonistic interactions, including those of economic concern, such as the successful deployment of biological control programs targeting pest organisms.
Insect-parasitoid interactions are among the most common antagonistic interactions in nature, where the survival of one player ultimately leads to the death of the other, resulting in strong selection for host resistance and parasite counter-resistance [32, 33]. Interactions between the phloem-feeding aphids (Hemiptera) and their hymenopteran parasitoids have received considerable attention (rev. ). Many aphids, including the pea aphid, Acyrthosiphon pisum, reproduce parthenogenetically for most of the year, such that variation in resistance among clonal lines to particular natural enemies can be examined. An important study by Henter and Via  found that some North American pea aphid clonal lines were totally resistant to attack by the prevalent parasitoid Aphidius ervi, while other clones were highly susceptible. Subsequent work found that European pea aphid clones also varied in resistance to the wasp A. ervi, as well as the more host-specific congener A. eadyi[36–38]. It was first assumed that variation in resistance resulted from immunological pathways encoded in the aphid genome, but later studies found that infection with heritable bacterial symbionts was responsible for a substantial portion of the observed variation . A number of studies identified correlations between infection with Hamiltonella defensa and increased clonal resistance to parasitism in the laboratory, but did not explicitly disentangle host- and symbiont-based effects (e.g. [40–42]). Simultaneous experimental studies, comparing aphid clones with and without symbionts, found that most H. defensa strains, and a single Serratia symbiotica strain, provided defense against the wasp A. ervi[39, 43–45]. Further investigation of this interaction found that bacteriophages called APSEs were required for H. defensa to confer protection to pea aphids [43, 46, 47] and that levels of resistance to the wasp varied greatly and correlated with symbiont strain and associated virus type; uninfected aphid clones (i.e. no facultative symbionts), on the other hand, exhibited limited variation in resistance and were highly susceptible to attack [43, 44]. Together, this work suggested that pea aphids primarily rely on infection with H. defensa and APSE to thwart attack from this common natural enemy. This hypothesis was bolstered by the observation that pea aphids have a weak encapsulation response to parasitism [48, 49]. A recent study, however, found two pea aphid clones exhibited substantial resistance to A. ervi in the absence of H. defensa or other facultative symbionts  indicating that aphid-based resistance persists in North American A. pisum populations and may contribute more to the observed variation in susceptibility than is currently appreciated. Aphid-encoded resistance to parasitism has also been reported in the peach-potato aphid, Myzus persicae, and the black bean aphid, Aphis fabae[50–52].
To examine the extent of pea aphid encoded variability in resistance to parasitism by the wasp A. ervi, we conducted parasitism assays across a range of aphid clones that were devoid of facultative symbionts. We also estimated the fecundity and longevity of several clonal lines of varying resistance to determine whether increases in resistance correlated with reductions in fitness, which would be expected if resistance is energetically costly.
Genetically distinct aphid clonal lines used in this study
Wisconsin, USA 1999
Sandstrom et. al. 
Utah, USA 2007
Martinez et. al. 
Utah, USA 2012
Utah, USA 2012
Utah, USA 2012
Utah, USA 2012
New York, USA 1998
Richards et. al.
Pennsylvania, USA 2011
Pennsylvania, USA 2010
Martinez et. al. 
Wisconsin, USA 2011
Wisconson, USA 2011
Pennsylvania, USA 2010
Martinez et. al. 
Georgia, USA 2010
Parker et. al. 
Georgia, USA 2008
Parker et. al. 
Georgia, USA 2008
Barribeau et. al. 
The solitary endoparasitoid, Aphidius ervi (Hymenoptera: Braconidae), also introduced from Europe, is the most prevalent parasitic wasp attacking A. pisum populations in North America . The wasps used in this study were obtained from a single, large, laboratory colony containing a mixture of A. ervi collected from Wisconsin and North Dakota, as well as commercially produced mummies (Arbico Organics). Wasps were reared continuously on a susceptible aphid line, AS3-AB; adults were provided with constant access to honey and water.
Microsatellite analyses to distinguish clonal lines
Microsatellite genotyping was used to confirm the identity and genetic variability between clonal aphid lines used in this study. DNA extractions of each aphid line were performed using an Omega EZNA® Tissue DNA Kit and were stored at -20°C until use. Four microsatellite loci— Ap-02, Ap-03, Ap-05 , and Aph10M —were PCR amplified with Dye Set-30 (DS-30) fluorescent primers using a touchdown reaction as follows: 94°C for 3 min; 45 cycles of 95°C for 30 s, 68–56°C touchdown for 13 cycles, then 55°C for 32 cycles, each cycle for 30 s, 72°C for 30 s; 72°C for final elongation, then held at 4°C. Fluorescent genotyping was then conducted by The Georgia Genomics Facility on an Applied Biosystems 3730xl DNA Analyzer, using the ROX500 size standard. Genotypic data were then analyzed using Geneious® version 6.1 (Biomatters).
Analysis of aphids typed at the four microsatellite loci revealed that all fifteen pea aphid lines used in this study represented distinct genotypes (See Additional file 1: Table S1 for details on loci used and allele sizes).
Aphid parasitism resistance assays to determine protective phenotype
Parasitism assays to determine the resistance phenotype were carried out on all aphid lines used in this study (Table 1) as in . Twenty 2nd to 3rd instar aphids were singly parasitized (each aphid is removed as it is parasitized) for each replicate (at least eight replicates) and placed on a fresh V. faba plant in a cup cage and held at 20 ± 1˚C and 50% relative humidity with a 16 L: 8D photoperiod. Prior studies have shown that isofemale lines of A. ervi wasps can vary in their counter-resistance (i.e. virulence), defined as their ability to successfully parasitize pea aphids , suggesting also that virulence, at least toward symbiont-mediated resistance, may evolve rapidly . Although we have not observed substantial variation in wasp virulence (Oliver, personal observation), we designed our parasitism assays to minimize such potential effects. In short, utilized wasps were collected haphazardly from our large laboratory culture (see above), which was maintained on a highly susceptible clone, and numerous female wasps were used to singly parasitize each line. After nine days, we counted the number of live aphids, dead aphids, and aphid mummies (dried aphids containing a wasp pupa) to determine the proportion of each measured as: survival (live aphids/20), mortality (dead aphids/20), and mummification (aphid mummies/20). A large majority of adult wasps eclose from mummies making them a suitable proxy for determining levels of successful parasitism . To determine background rates of mortality for each line, we placed five replicates of twenty unparasitized 2nd to 3rd instar aphids from each line on fresh plants and mortality was recorded from the control lines after nine days.
Aphid fitness assays
We conducted cumulative fecundity assays under permissive conditions (no aphid or plant stresses) to investigate potential tradeoffs between parasitoid resistance and aphid fecundity. Six aphid lines, those with the most (WA4-AB, ZA17-AB, CJ1-13) and least resistance (G15, AS3-AB, LSR01) to A. ervi (See parasitism assay results), were selected for this assay. Prior to the experiment, each aphid line was reared on multiple plants, chosen haphazardly, from a cohort of healthy plants of similar age and size for several generations in 16 L:8D intervals at 20°C in a Percival I-41LLVL environmental incubator to reduce effects resulting from variation in prior culturing (i.e. maternal and grandmaternal effects). From these cultures, approximately twenty adults from each line were placed on a fresh plant and allowed to reproduce for 17 ± 1 h before removal. The resulting offspring were left to mature until they were 48 ± 8.5 h-old and then six nymphs (x8 replicates = 48 aphids per line) were placed in a cup cage containing a single Vicia faba plant. Cages were examined at 3-day intervals. At these times, the numbers of live and dead aphids of the original cohort were recorded to measure longevity, while the numbers of offspring produced were recorded to measure fecundity. Offspring were discarded at the time of counting to prevent their growth to maturity and subsequent offspring production as in .
Aphid survival, mortality, and mummification (see above) were determined for each replicate of each parasitized aphid line. These values were used to compare differences among aphid lines using a Generalized Linear Model (GzLM), with a binomial distribution and logit link function. Survival, mortality, and mummification data were mildly overdispersed and so final test values are reported with a quasibinomial adjustment. A Post hoc Tukey’s HSD test on aphid survival, mortality, and mummification was performed using an ANOVA of arcsine transformed proportional data for pairwise comparisons among aphid lines. GzLM was also used to compare mortality of parasitized and control (unparasitized) aphids, both within and across lines (see Additional file 2: Figure S1). As aphid mortality after parasitism may be tied to differences among aphid lines, linear regression was performed on mean mortality between unparasitized and parasitized aphids among all lines used (see Additional file 2: Figure S1). Mean mortality was natural log transformed to satisfy normality assumptions of the linear regression.
Several analyses were employed to compare fitness parameters (fecundity and longevity) between aphids with high and low resistance to parasitism. Linear mixed models with heterogeneous first order auto regressive (ARH1) covariance structure (to account for repeated measures) were used to examine the effect of aphid line and resistance on cumulative aphid fecundity through several time points. Multivariate analysis of variance (MANOVA) with repeated measures design was used to examine the effect of aphid line and resistance on aphid longevity. All analyses comparing the effect of resistance on aphid fecundity or longevity were done by nesting ‘aphid genotype’ (six aphid lines) within ‘resistance’ (high or low).
The majority of our A. pisum clones (12/15) were collected from alfalfa. To determine if there is significant variation in susceptibility among clones of this host race we conducted a restricted analysis and found similar variation in survival, mortality, and mummification (GzLM df = 11; χ2 = 389.2, 38.24, 344.82; p < 0.0001, < 0.0001, and < 0.0001; respectively).
Mortality also varied significantly among control lines not exposed to wasps (2 – 15%; GzLM, df = 14, χ2 = 24.45, p = 0.0404), and parasitism often resulted in significant increases in mortality relative to controls of the same line (Additional file 2: Figure S1). A linear regression analysis found no correlation between mortality of unparasitized controls and parasitized treatments (Linear Regression, F1, 13 = 2.02, p = 0.1784) indicating that parasitism-induced mortality affects clonal lines differently than their background mortality.
Aphid fitness assays
Effect of aphid genotype and resistance phenotype on fecundity and longevity
Aphid fecundity (Cumulative)
(A) Aphid line
(C) Aphid line
Substantial variability in aphid-based resistance to parasitism
Pea aphids have been previously shown to exhibit substantial clonal variation in susceptibility to the parasitic wasp A. ervi (e.g. [35, 36], with more recent studies showing that infection with the heritable protective symbiont H. defensa contributes much of the observed variation [12, 43, 44]. In these latter studies, a total of eleven uninfected clones were all highly susceptible to attack, while infection with H. defensa resulted in varying levels of protection correlating with symbiont strain and associated bacteriophage haplotype [12, 43, 44, 75]. Due to the limited number of aphid clones used in these studies, however, it remained unclear whether there was also appreciable variation in resistance encoded by the aphid genotype. Using fifteen clonal pea aphid lines free of H. defensa and other facultative symbionts, we report here that there is indeed extensive aphid-encoded variation for resistance to A. ervi (Figure 1). In fact, the six most highly resistant clones (Figure 1) exhibit levels of defense (~55 – 75% survival) comparable to those contributed by defensive symbionts (~35 – 100% survival) [12, 43, 44, 71].
These findings indicate that pea aphids employ both aphid- and symbiont-based strategies to aid in their interactions with this prevalent natural enemy. In addition to aphid- and H. defensa encoded protection, other common aphid symbionts, including S. symbiotica, or combinations of symbionts [42, 45, 76] show promise in influencing interactions with wasps. To date, however, the majority of uninfected clones (including those in this study: 21/27) examined in laboratory studies were found to be >65% susceptible to attack by this wasp [12, 39, 43, 44, 75] suggesting that symbiont-based protection may be the most frequently used line of defense. However, infection frequencies of H. defensa are quite variable (10 to 58%) in N. American field populations , and there may be dynamic temporal and spatial variation in the relative proportions of each mode of defense. This, of course, depends on the efficacy of symbiont- and aphid-based defenses under natural conditions, which is largely unknown [77, 78]. Temperature, for example, is known to affect A. pisum clonal resistance to parasitism and appears to be due primarily to losses in H. defensa-mediated protection at higher temperatures , but these assays were not conducted while controlling for aphid genotype and hence it is possible that temperature also impacts aphid-encoded resistance. If higher temperature indeed impacts symbiont-based resistance to a greater degree, then we would expect fewer H. defensa-bearing aphids and more aphid-encoded resistance in warmer regions and seasons.
The majority of clones we examined were collected from alfalfa (Table 1), and an analysis restricted to this host race also recovered substantial variation in susceptibility to parasitism (Figure 1). Additional studies are required to determine if there is substantial aphid-encoded variation in susceptibility within populations or whether there is geographical variation among collection sites. We did not detect significant variation among sites in this study, but the sampling was very limited. Facultative symbiont infection frequencies are known to vary among pea aphid host races, and infection with H. defensa occurs more frequently on alfalfa than on other host plants [63, 64]. We might predict that aphid-encoded defenses against A. ervi are more common in other host races, such as clover, with lower H. defensa infection frequencies. One study, however, reported that variation in aphid resistance (due to any mechanism) was much lower on clover (~60 - 95% susceptible), compared to alfalfa (~5 – 90% susceptible), and that clover clones were generally more susceptible than alfalfa clones to parasitism by A. ervi. One possible explanation for the presence of both higher H. defensa infection frequencies and more aphid-encoded protection on alfalfa is that clover-derived A. pisum suffer reduced rates of attack under field conditions resulting in less selection pressure for the evolution and maintenance of resistance. However, we caution that further work is needed to evaluate the ranges of aphid-encoded resistance on clover (and other host races) and the importance of the various resistance components under field conditions.
The mechanisms underlying this aphid-based resistance to parasitism are unknown. The pea aphid lacks a strong encapsulation response, the innate cellular immune response used by many insects to encapsulate and asphyxiate invading parasitoid eggs [48, 49, 79]. Sequencing of the pea aphid genome revealed several pathways (e.g. IMD) involved in innate immunity against pathogenic microbes were missing, yet this aphid retains important pathways associated with encapsulation  and are able to melanize foreign objects . We are currently investigating the phenology and mechanisms underlying both symbiont- and aphid-based immunity to this wasp.
Pea aphids also show clonal variation in susceptibility to the aphid-specific fungal entomopathogen Pandora neoaphidis (e.g. ). The heritable symbiont Regiella insecticola and other symbionts have been shown to confer protection against this and other specific fungal pathogens and thus contribute to variation in resistance [81–83]. More recent work indicates that pea aphids also show aphid-based clonal variation in their susceptibility to Pandora, indicating both aphid- and symbiont-based defensive strategies are utilized against diverse natural enemies. It will be interesting to determine if there is a negative correlation in resistance to parasitoids and fungal pathogens, providing a potential explanation for the persistence of susceptible genotypes. In addition, we are seeking to determine whether resistant genotypes are less likely to carry protective symbionts, as services are duplicated. Recently, two H. defensa strains were found not to confer any additional protection beyond that of their resistant host aphid genotype  suggesting this may be the case, although it is also possible these strains would confer protection in a susceptible background, but that benefits are not additive. Duplication in defense, though, could partially explain why the beneficial symbiont H. defensa is not more prevalent in field populations [3, 12, 78].
The black bean aphid, Aphis fabae, also shows variation in resistance to its common parasitoid Lysiphlebus fabarum, with some variation encoded by the defensive symbiont H. defensa and some likely encoded by the host genome . Other aphids, including Aphis craccivora and Myzus persicae show clonal variation in susceptibility to parasitoids, including evidence for both symbiont- and host-encoded resistance [50, 51, 85] indicating that aphids generally use a variety of mechanisms to aid in their defense.
Populations of the parasitoid A. ervi have also been shown to exhibit variation in the ability to successfully parasitize pea aphids , but further work in this system is needed to determine whether there is variation in counter-resistance toward particular components of aphid defense. Such specificity in genotype by genotype interactions may be directed toward either aphid- or symbiont-based components of resistance, and while duplicated services may not provide an advantage against the average wasp genotype, it may provide protection against a wider range of enemy genotypes. As mentioned above, the wasp A. ervi appears capable of evolving virulence toward symbiont-based protection , but it is unclear if it can do so against aphid-based defenses. Such genotype by genotype interactions have been best studied in the black bean aphid-H. defensa-L. fabarum interaction, where they occur between parasitoid genotypes and defensive symbiont strains, but have not been found between parasitoid and uninfected host genotypes [52, 86, 87]. If wasps more readily evolve counter-resistance to symbiont-encoded resistance, this may lead to an increase in the frequency of H. defensa-free resistant clones in natural populations, or vice versa.
No apparent trade-offs between parasitoid resistance and fitness
The maintenance of clonal variation in pea aphid susceptibility to the parasitoid A. ervi could be explained by tradeoffs in other functions given limited resources. Aphids, including A. pisum, have evolved a number of life history traits associated with increasing reproductive output, including cyclical parthenogenesis, wing polyphenisms, and telescoping generations . Thus, if aphid-based resistance to parasitism carries constitutive costs, then we might expect to see a negative correlation between resistance and fecundity or longevity. While we did find significant clonal variation in fecundity, we did not find a positive correlation between susceptibility and fecundity or longevity among the most and least resistant lines (Figure 2; Table 2). Tradeoffs between resistance and aspects of host fitness, including development time, survival, and fecundity have been observed in other systems [20, 22–24], but they are often difficult to detect in aphid systems [36, 51]. One study  did find a tradeoff between resistance and fecundity among ten clonal pea aphid lines, but it is unclear if resistance was symbiont or aphid-based.
One possible reason we did not find the expected trade-off is that costs are induced rather than constitutive, such that costs are only manifested upon attack. We are currently investigating fecundity among parasitized clonal lines and other sub-lethal effects of parasitism, but preliminary trials indicate parasitized aphids that survive have similar fecundity to unparasitized controls (AJM unpublished). It is also possible that tradeoffs may only become apparent under more stressful conditions or when clones are in direct competition for resources, as our lab assays were conducted using lines held separately and reared under very permissive conditions . For example, Kraaijeveld and Godfray  found trade-offs resulting from increased parasitoid resistance in Drosophila melanogaster, but these were only observable under high intraspecific competition for food resources. Costs associated with H. defensa-mediated resistance have also been difficult to detect in component fitness assays. Only when H. defensa-infected and uninfected lines sharing the same genotypes were reared together in population cages were costs to infection identified . Thus, costs may become apparent under more realistic conditions, with varying biotic (e.g. plant quality) and abiotic factors (e.g. water stress, temperature), and when intra- and interspecific competition is present.
Here we show that pea aphid genomes maintain variation in susceptibility to a common natural enemy, the parasitoid A. ervi. Together, with prior work showing that infection with the heritable symbiont H. defensa confers varying levels of protection, depending on strain and phage type, it is clear that this aphid employs multiple strategies to thwart attack from parasitoids. It remains unclear whether resistant aphid genotypes and protective symbionts like H. defensa interact, or whether effects are additive or redundant, as this would be an important factor influencing the spread of symbiont- and aphid-based resistance in natural populations. It is important to understand the sources and amount of variation in resistance to common natural enemies, and how each is impacted by biotic and abiotic interactions. Temperature, for example, may differentially influence wasp and aphid behavioral responses and also affect the performance of aphid- and symbiont-encoded resistance  depending on presence and type of defense. Multiple sources of resistance may limit the evolution of resistance (when, for e.g., both types are employed in same host) or generate complex genotype by genotype interactions where some wasp genotypes specialize on particular aphid clone-symbiont strain combinations. Understanding the sources and dynamics of resistance is also important for the effective management of pest populations. If resistance is due primarily to symbionts, for example, then a quick diagnostic screen may inform whether biological control applications are likely to be effective.
Availability of supporting data
We would like to thank Kyungsun Kim for her technical support. We thank Edward Evans, Brandon Barton, Anthony Ives, Andrew Smith, and Benjamin Parker for help collecting aphid samples. We also thank Dr. Kim Love-Myers, Hsien-Lin Hsieh, and Xijue Tan for their statistical advice. This project was supported by National Science Foundation awards 1050128 and 1240892.
- Fellowes MDE, Kraaijeveld AR, Godfray HCJ: Association between feeding rate and parasitoid resistance in Drosophila melanogaster. Evolution. 1999, 53 (4): 1302-1305. 10.2307/2640834.View ArticleGoogle Scholar
- Jaenike J, Unckless R, Cockburn SN, Boelio LM, Perlman SJ: Adaptation via symbiosis: recent spread of a Drosophila defensive symbiont. Science. 2010, 329 (5988): 212-215. 10.1126/science.1188235.PubMedView ArticleGoogle Scholar
- Oliver KM, Campos J, Moran NA, Hunter MS: Population dynamics of defensive symbionts in aphids. Proc Biol Sci. 2008, 275 (1632): 293-299. 10.1098/rspb.2007.1192.PubMedPubMed CentralView ArticleGoogle Scholar
- Moller AP: Effects of a haematophagous mite on the barn swallow (Hirundo rustica): a test of the Hamilton and Zuk hypothesis. Evolution. 1990, 44 (4): 771-784. 10.2307/2409545.View ArticleGoogle Scholar
- Spitze K: Predator-mediated plasticity of prey life history and morphology: Chaoborus americanus predation on Daphnia pulex. Am Nat. 1992, 139 (2): 229-247. 10.1086/285325.View ArticleGoogle Scholar
- Grosholz ED: The effects of host genotype and spatial distribution on trematode parasitism in a bivalve population. Evolution. 1994, 48 (5): 1514-1524. 10.2307/2410245.View ArticleGoogle Scholar
- Boulinier T, Sorci G, Monnat JY, Danchin E: Parent‒offspring regression suggests heritable susceptibility to ectoparasites in a natural population of kittiwake Rissa tridactyla. J Evol Biol. 1997, 10 (1): 77-85. 10.1007/s000360050010.View ArticleGoogle Scholar
- Ebert D, Zschokke-Rohringer CD, Carius HJ: Within–and between–population variation for resistance of Daphnia magna to the bacterial endoparasite Pasteuria ramosa. Proc R Soc Lond B Biol Sci. 1998, 265 (1410): 2127-2134. 10.1098/rspb.1998.0549.View ArticleGoogle Scholar
- Brinkhof MW, Heeb P, Kölliker M, Richner H: Immunocompetence of nestling great tits in relation to rearing environment and parentage. Proc R Soc Lond B Biol Sci. 1999, 266 (1435): 2315-2322. 10.1098/rspb.1999.0925.View ArticleGoogle Scholar
- Smith JA, Wilson K, Pilkington JG, Pemberton JM: Heritable variation in resistance to gastro-intestinal nematodes in an unmanaged mammal population. Proc R Soc Lond B Biol Sci. 1999, 266 (1425): 1283-1290. 10.1098/rspb.1999.0776.View ArticleGoogle Scholar
- Carius HJ, Little TJ, Ebert D: Genetic variation in a host‒parasite association: potential for coevolution and frequency‒dependent selection. Evolution. 2001, 55 (6): 1136-1145. 10.1111/j.0014-3820.2001.tb00633.x.PubMedView ArticleGoogle Scholar
- Martinez AJ, Weldon SR, Oliver KM: Effects of parasitism on aphid nutritional and protective symbioses. Mol Ecol. 2014, 23 (6): 1594-1607. 10.1111/mec.12550.PubMedView ArticleGoogle Scholar
- Sadd BM, Schmid-Hempel P: Principles of ecological immunology. Evol Appl. 2009, 2 (1): 113-121.PubMedPubMed CentralView ArticleGoogle Scholar
- Parker BJ, Barribeau SM, Laughton AM, de Roode JC, Gerardo NM: Non-immunological defense in an evolutionary framework. Trends Ecol Evol. 2011, 26 (5): 242-248. 10.1016/j.tree.2011.02.005.PubMedView ArticleGoogle Scholar
- Evison SEF, Fazio G, Chappell P, Foley K, Jensen AB, Hughes WOH: Host-parasite genotypic interactions in the honey bee: the dynamics of diversity. Ecol Evol. 2013, 3 (7): 2214-2222. 10.1002/ece3.599.PubMedPubMed CentralView ArticleGoogle Scholar
- Sadd BM, Barribeau SM: Heterogeneity in infection outcome: lessons from a bumblebee-trypanosome system. Parasite Immunol. 2013, 35 (11): 339-349.Google Scholar
- Rolff J, Siva-Jothy MT: Invertebrate ecological immunology. Science. 2003, 301 (5632): 472-475. 10.1126/science.1080623.PubMedView ArticleGoogle Scholar
- Schmid-Hempel P: Evolutionary ecology of insect immune defenses. Annu Rev Entomol. 2005, 50: 529-551. 10.1146/annurev.ento.50.071803.130420.PubMedView ArticleGoogle Scholar
- Sutter GR, Rothenbuhler WC, Raun ES: Resistance to American foulbrood in honey bees: VII. Growth of resistant and susceptible larvae. J Invertebr Pathol. 1968, 12 (1): 25-28. 10.1016/0022-2011(68)90239-5.View ArticleGoogle Scholar
- Yan G, Severson DW, Christensen BM: Costs and benefits of mosquito refractoriness to malaria parasites: implications for genetic variability of mosquitoes and genetic control of malaria. Evolution. 1997, 51 (2): 441-450. 10.2307/2411116.View ArticleGoogle Scholar
- Kraaijeveld A, Godfray H: Trade-off between parasitoid resistance and larval competitive ability in Drosophila melanogaster. Nature. 1997, 389 (6648): 278-280. 10.1038/38483.PubMedView ArticleGoogle Scholar
- Boots M, Begon M: Trade-offs with resistance to a granulosis virus in the Indian meal moth, examined by a laboratory evolution experiment. Funct Ecol. 1993, 7 (5): 528-534. 10.2307/2390128.View ArticleGoogle Scholar
- Armitage SAO, Thompson JJW, Rolff J, Siva-Jothy MT: Examining costs of induced and constitutive immune investment in Tenebrio molitor. J Evol Biol. 2003, 16 (5): 1038-1044. 10.1046/j.1420-9101.2003.00551.x.PubMedView ArticleGoogle Scholar
- Webster J, Woolhouse M: Cost of resistance: relationship between reduced fertility and increased resistance in a snail—schistosome host—parasite system. Proc R Soc Lond B Biol Sci. 1999, 266 (1417): 391-396. 10.1098/rspb.1999.0650.View ArticleGoogle Scholar
- Chaboudez P, Burdon J: Frequency-dependent selection in a wild plant-pathogen system. Oecologia. 1995, 102 (4): 490-493. 10.1007/BF00341361.View ArticleGoogle Scholar
- Koskella B, Lively CM: Evidence for negative frequency-dependent selection during experimental coevolution of a freshwater snail and sterilizing trematode. Evolution. 2009, 63 (9): 2213-2221. 10.1111/j.1558-5646.2009.00711.x.PubMedView ArticleGoogle Scholar
- Foster SP, Tomiczek M, Thompson R, Denholm I, Poppy G, Kraaijeveld AR, Powell W: Behavioural side-effects of insecticide resistance in aphids increase their vulnerability to parasitoid attack. Anim Behav. 2007, 74 (3): 621-632. 10.1016/j.anbehav.2006.12.018.View ArticleGoogle Scholar
- Bryan-Walker K, Leung TL, Poulin R: Local adaptation of immunity against a trematode parasite in marine amphipod populations. Mar Biol. 2007, 152 (3): 687-695. 10.1007/s00227-007-0725-x.View ArticleGoogle Scholar
- Sanders AE, Scarborough C, Layen SJ, Kraaijeveld AR, Godfray HCJ: Evolutionary change in parasitoid resistance under crowded conditions in Drosophila melanogaster. Evolution. 2005, 59 (6): 1292-1299. 10.1111/j.0014-3820.2005.tb01779.x.PubMedView ArticleGoogle Scholar
- Luong L, Polak M: Environment-dependent trade-offs between ectoparasite resistance and larval competitive ability in the Drosophila–Macrocheles system. Heredity. 2007, 99 (6): 632-640. 10.1038/sj.hdy.6801040.PubMedView ArticleGoogle Scholar
- Triggs A, Knell RJ: Interactions between environmental variables determine immunity in the Indian meal moth Plodia interpunctella. J Anim Ecol. 2012, 81 (2): 386-394. 10.1111/j.1365-2656.2011.01920.x.PubMedView ArticleGoogle Scholar
- Godfray HCJ: Parasitoids: Behavioral and Evolutionary Ecology. 1994, Princeton: Princeton University PressGoogle Scholar
- Kraaijeveld AR, Godfray HCJ: Evolution of Host Resistance and Parasitoid Counter-Resistance. Advances in Parasitology, Vol 70: Parasitoids of Drosophila, Volume 70. Edited by: Prevost G. 2009, 257-280.View ArticleGoogle Scholar
- Le Ralec A, Anselme C, Outreman Y, Poirie M, van Baaren J, Le Lann C, van Alphen JJM: Evolutionary ecology of the interactions between aphids and their parasitoids. C R Biol. 2010, 333 (6–7): 554-565.PubMedView ArticleGoogle Scholar
- Henter HJ, Via S: The potential for coevolution in a host-parasitoid system 1. Genetic variation within a an aphid population in susceptibility to a parasitic wasp. Evolution. 1995, 49 (3): 427-438. 10.2307/2410267.View ArticleGoogle Scholar
- Ferrari J, Muller CB, Kraaijeveld AR, Godfray HCJ: Clonal variation and covariation in aphid resistance to parasitoids and a pathogen. Evolution. 2001, 55 (9): 1805-1814. 10.1111/j.0014-3820.2001.tb00829.x.PubMedView ArticleGoogle Scholar
- Gwynn DM, Callaghan A, Gorham J, Walters KFA, Fellowes MDE: Resistance is costly: trade-offs between immunity, fecundity and survival in the pea aphid. Proc R Soc Lond B Biol Sci. 2005, 272 (1574): 1803-1808. 10.1098/rspb.2005.3089.View ArticleGoogle Scholar
- Stacey DA, Fellowes MDE: Influence of temperature on pea aphid Acyrthosiphon pisum (Hemiptera: Aphididae) resistance to natural enemy attack. Bull Entomol Res. 2002, 92 (4): 351-357.PubMedView ArticleGoogle Scholar
- Oliver KM, Russell JA, Moran NA, Hunter MS: Facultative bacterial symbionts in aphids confer resistance to parasitic wasps. Proc Natl Acad Sci U S A. 2003, 100 (4): 1803-1807. 10.1073/pnas.0335320100.PubMedPubMed CentralView ArticleGoogle Scholar
- Bensadia F, Boudreault S, Guay JF, Michaud D, Cloutier C: Aphid clonal resistance to a parasitoid fails under heat stress. J Insect Physiol. 2006, 52 (2): 146-157. 10.1016/j.jinsphys.2005.09.011.PubMedView ArticleGoogle Scholar
- Ferrari J, Darby AC, Daniell TJ, Godfray HCJ, Douglas AE: Linking the bacterial community in pea aphids with host-plant use and natural enemy resistance. Ecol Entomol. 2004, 29 (1): 60-65. 10.1111/j.1365-2311.2004.00574.x.View ArticleGoogle Scholar
- Guay JF, Boudreault S, Michaud D, Cloutier C: Impact of environmental stress on aphid clonal resistance to parasitoids: role of Hamiltonella defensa bacterial symbiosis in association with a new facultative symbiont of the pea aphid. J Insect Physiol. 2009, 55 (10): 919-926. 10.1016/j.jinsphys.2009.06.006.PubMedView ArticleGoogle Scholar
- Oliver KM, Degnan PH, Hunter MS, Moran NA: Bacteriophages encode factors required for protection in a symbiotic mutualism. Science. 2009, 325 (5943): 992-994. 10.1126/science.1174463.PubMedView ArticleGoogle Scholar
- Oliver KM, Moran NA, Hunter MS: Variation in resistance to parasitism in aphids is due to symbionts not host genotype. Proc Natl Acad Sci. 2005, 102 (36): 12795-12800. 10.1073/pnas.0506131102.PubMedPubMed CentralView ArticleGoogle Scholar
- Oliver KM, Moran NA, Hunter MS: Costs and benefits of a superinfection of facultative symbionts in aphids. Proc R Soc Lond B Biol Sci. 2006, 273 (1591): 1273-1280. 10.1098/rspb.2005.3436.View ArticleGoogle Scholar
- Degnan PH, Moran NA: Diverse phage-encoded toxins in a protective insect endosymbiont. Appl Environ Microbiol. 2008, 74 (21): 6782-6791. 10.1128/AEM.01285-08.PubMedPubMed CentralView ArticleGoogle Scholar
- Moran NA, Degnan PH, Santos SR, Dunbar HE, Ochman H: The players in a mutualistic symbiosis: insects, bacteria, viruses, and virulence genes. Proc Natl Acad Sci U S A. 2005, 102 (47): 16919-16926. 10.1073/pnas.0507029102.PubMedPubMed CentralView ArticleGoogle Scholar
- Carver M, Sullivan DJ: Encapsulative Defense Reactions of Aphids (Hemiptera: Aphididae) to Insect Parasitoids (Hymenoptera: Aphidiidae and Aphelinidae) (Minireview). Ecology and Effectiveness of Aphidophaga. Edited by: Niemczyk E, Dixon AFG. 1988, The Netherlands: SPB Academic, 299-303.Google Scholar
- Laughton AM, Garcia JR, Altincicek B, Strand MR, Gerardo NM: Characterisation of immune responses in the pea aphid, Acyrthosiphon pisum. J Insect Physiol. 2011, 57 (6): 830-839. 10.1016/j.jinsphys.2011.03.015.PubMedView ArticleGoogle Scholar
- Vorburger C, Gehrer L, Rodriguez P: A strain of the bacterial symbiont Regiella insecticola protects aphids against parasitoids. Biol Lett. 2010, 6 (1): 109-111. 10.1098/rsbl.2009.0642.PubMedPubMed CentralView ArticleGoogle Scholar
- von Burg S, Ferrari J, Müller CB, Vorburger C: Genetic variation and covariation of susceptibility to parasitoids in the aphid Myzus persicae: no evidence for trade-offs. Proc R Soc Lond B Biol Sci. 2008, 275 (1638): 1089-1094. 10.1098/rspb.2008.0018.View ArticleGoogle Scholar
- Sandrock C, Gouskov A, Vorburger C: Ample genetic variation but no evidence for genotype specificity in an all-parthenogenetic host-parasitoid interaction. J Evol Biol. 2010, 23 (3): 578-585. 10.1111/j.1420-9101.2009.01925.x.PubMedView ArticleGoogle Scholar
- Caillaud MC, Via S: Specialized feeding behavior influences both ecological specialization and assortative mating in sympatric host races of pea aphids. Am Nat. 2000, 156 (6): 606-621. 10.1086/316991.View ArticleGoogle Scholar
- Ferrari J, Godfray HCJ, Faulconbridge AS, Prior K, Via S: Population differentiation and genetic variation in host choice among pea aphids from eight host plant genera. Evolution. 2006, 60 (8): 1574-1584. 10.1111/j.0014-3820.2006.tb00502.x.PubMedView ArticleGoogle Scholar
- Ferrari J, Scarborough CL, Godfray HCJ: Genetic variation in the effect of a facultative symbiont on host-plant use by pea aphids. Oecologia. 2007, 153 (2): 323-329. 10.1007/s00442-007-0730-2.PubMedView ArticleGoogle Scholar
- Ferrari J, Via S, Godfray HCJ: Population differentiation and genetic variation in performance on eight hosts in the pea aphid complex. Evolution. 2008, 62 (10): 2508-2524. 10.1111/j.1558-5646.2008.00468.x.PubMedView ArticleGoogle Scholar
- Frantz A, Plantegenest M, Mieuzet L, Simon JC: Ecological specialization correlates with genotypic differentiation in sympatric host-populations of the pea aphid. J Evol Biol. 2006, 19 (2): 392-401. 10.1111/j.1420-9101.2005.01025.x.PubMedView ArticleGoogle Scholar
- Peccoud J, Simon JC, McLaughlin HJ, Moran NA: Post-Pleistocene radiation of the pea aphid complex revealed by rapidly evolving endosymbionts. Proc Natl Acad Sci U S A. 2009, 106 (38): 16315-16320. 10.1073/pnas.0905129106.PubMedPubMed CentralView ArticleGoogle Scholar
- Hufbauer RA, Via S: Evolution of an aphid-parasitoid interaction: variation in resistance to parasitism among aphid populations specialized on different plants. Evolution. 1999, 53 (5): 1435-1445. 10.2307/2640890.View ArticleGoogle Scholar
- Via S, Bouck AC, Skillman S: Reproductive isolation between divergent races of pea aphids on two hosts. II. Selection against migrants and hybrids in the parental environments. Evolution. 2000, 54 (5): 1626-1637. 10.1111/j.0014-3820.2000.tb00707.x.PubMedView ArticleGoogle Scholar
- Eastop VF: A taxonomic study of australian aphidoidea (Homoptera). Aust J Zool. 1966, 14 (3): 399-592. 10.1071/ZO9660399.View ArticleGoogle Scholar
- Brisson JA, Nuzhdin SV, Stern DL: Similar patterns of linkage disequilibrium and nucleotide diversity in native and introduced populations of the pea aphid, Acyrthosiphon pisum. BMC Genet. 2009, 10: 22-PubMedPubMed CentralView ArticleGoogle Scholar
- Ferrari J, West JA, Via S, Godfray HCJ: Population genetic structure and secondary symbionts in host-associated populations of the pea aphid complex. Evolution. 2012, 66 (2): 375-390. 10.1111/j.1558-5646.2011.01436.x.PubMedView ArticleGoogle Scholar
- Russell JA, Weldon S, Smith AH, Kim KL, Hu Y, Łukasik P, Doll S, Anastopoulos I, Novin M, Oliver KM: Uncovering symbiont‒driven genetic diversity across North American pea aphids. Mol Ecol. 2013, 22 (7): 2045-2059. 10.1111/mec.12211.PubMedView ArticleGoogle Scholar
- Lamb R, Pointing P: Sexual morph determination in the aphid, Acyrthosiphon pisum. J Insect Physiol. 1972, 18 (10): 2029-2042. 10.1016/0022-1910(72)90170-9.View ArticleGoogle Scholar
- Sandstrom JP, Russell JA, White JP, Moran NA: Independent origins and horizontal transfer of bacterial symbionts of aphids. Molecular Ecology. 2001, 10 (1): 217-228. 10.1046/j.1365-294X.2001.01189.x.PubMedView ArticleGoogle Scholar
- Richards S, Gibbs RA, Gerardo NM, Moran N, Nakabachi A, Stern D, Tagu D, Wilson ACC, Muzny D, Kovar C, et al: Genome sequence of the Pea Aphid Acyrthosiphon pisum. PLoS Biol. 2010, 8 (2): 24-Google Scholar
- Parker BJ, Garcia JR, Gerardo NM: Genetic variation in resistance and fecundity tolerance in a natural host–pathogen interaction. Evolution. 2014, in pressGoogle Scholar
- Barribeau SM, Sok D, Gerardo NM: Aphid reproductive investment in response to mortality risks. BMC Evol Biol. 2010, 10: 11-10.1186/1471-2148-10-11.View ArticleGoogle Scholar
- Angalet G, Fuester R: The Aphidius parasites of the pea aphid Acyrthosiphon pisum in the eastern half of the United States. Ann Entomol Soc Am. 1977, 70 (1): 87-96.View ArticleGoogle Scholar
- Kurokawa T, Yao I, Akimoto S, Hasegawa E: Isolation of six microsatellite markers from the pea aphid, Acyrthosiphon pisum (Homoptera, Aphididae). Mol Ecol Notes. 2004, 4 (3): 523-524. 10.1111/j.1471-8286.2004.00712.x.View ArticleGoogle Scholar
- Caillaud M, Mondor‒Genson G, Levine‒Wilkinson S, Mieuzet L, Frantz A, Simon J, D’Acier Coeur A: Microsatellite DNA markers for the pea aphid Acyrthosiphon pisum. Mol Ecol Notes. 2004, 4 (3): 446-448. 10.1111/j.1471-8286.2004.00676.x.View ArticleGoogle Scholar
- Henter HJ: The potential for coevolution in a host-parasitoid system. II. Genetic variation within a population of wasps in the ability to parasitize an aphid host. Evolution. 1995, 49 (3): 439-445. 10.2307/2410268.View ArticleGoogle Scholar
- Dion E, Zele F, Simon JC, Outreman Y: Rapid evolution of parasitoids when faced with the symbiont-mediated resistance of their hosts. J Evol Biol. 2011, 24 (4): 741-750. 10.1111/j.1420-9101.2010.02207.x.PubMedView ArticleGoogle Scholar
- Oliver KM, Noge K, Huang EM, Campos JM, Becerra JX, Hunter MS: Parasitic wasp responses to symbiont-based defense in aphids. BMC Biol. 2012, 10 (1): 11-10.1186/1741-7007-10-11.PubMedPubMed CentralView ArticleGoogle Scholar
- Nyabuga FN, Outreman Y, Simon JC, Heckel DG, Weisser WW: Effects of pea aphid secondary endosymbionts on aphid resistance and development of the aphid parasitoid Aphidius ervi: a correlative study. Entomol Exp Appl. 2010, 136 (3): 243-253.Google Scholar
- Bilodeau E, Simon JC, Guay JF, Turgeon J, Cloutier C: Does variation in host plant association and symbiont infection of pea aphid populations induce genetic and behaviour differentiation of its main parasitoid, Aphidius ervi?. Evol Ecol. 2013, 27 (1): 165-184. 10.1007/s10682-012-9577-z.View ArticleGoogle Scholar
- Oliver KM, Smith AH, Russell JA: Defensive symbiosis in the real world – advancing ecological studies of heritable, protective bacteria in aphids and beyond. Funct Ecol. 2014, 28 (2): 341-355. 10.1111/1365-2435.12133.View ArticleGoogle Scholar
- Strand MR, Pech LL: Immunological basis for compatibility in parasitoid host relationships. Annu Rev Entomol. 1995, 40: 31-56. 10.1146/annurev.en.40.010195.000335.PubMedView ArticleGoogle Scholar
- Gerardo NM, Altincicek B, Anselme C, Atamian H, Barribeau SM, De Vos M, Duncan EJ, Evans JD, Gabaldon T, Ghanim M, Heddi A, Kaloshian I, Latorre A, Moya A, Nakabachi A, Parker BJ, Perez-Brocal V, Pignatelli M, Rahbe Y, Ramsey JS, Spragg CJ, Tamames J, Tamarit D, Tamborindeguy C, Vincent-Monegat C, Vilcinskas A: Immunity and other defenses in pea aphids, Acyrthosiphon pisum. Genome Biol. 2010, 11 (2): R21-10.1186/gb-2010-11-2-r21.PubMedPubMed CentralView ArticleGoogle Scholar
- Lukasik P, van Asch M, Guo HF, Ferrari J, Godfray HCJ: Unrelated facultative endosymbionts protect aphids against a fungal pathogen. Ecol Lett. 2013, 16 (2): 214-218. 10.1111/ele.12031.PubMedView ArticleGoogle Scholar
- Parker BJ, Spragg CJ, Altincicek B, Gerardo NM: Symbiont-mediated protection against fungal pathogens in Pea Aphids: a role for pathogen specificity?. Appl Environ Microbiol. 2013, 79 (7): 2455-2458. 10.1128/AEM.03193-12.PubMedPubMed CentralView ArticleGoogle Scholar
- Scarborough CL, Ferrari J, Godfray HCJ: Aphid protected from pathogen by endosymbiont. Science. 2005, 310 (5755): 1781-1781. 10.1126/science.1120180.PubMedView ArticleGoogle Scholar
- Schmid M, Sieber R, Zimmermann YS, Vorburger C: Development, specificity and sublethal effects of symbiont-conferred resistance to parasitoids in aphids. Funct Ecol. 2012, 26 (1): 207-215. 10.1111/j.1365-2435.2011.01904.x.View ArticleGoogle Scholar
- Desneux N, Barta RJ, Hoelmer KA, Hopper KR, Heimpel GE: Multifaceted determinants of host specificity in an aphid parasitoid. Oecologia. 2009, 160 (2): 387-398. 10.1007/s00442-009-1289-x.PubMedView ArticleGoogle Scholar
- Cayetano L, Vorburger C: Genotype-by-genotype specificity remains robust to average temperature variation in an aphid/endosymbiont/parasitoid system. J Evol Biol. 2013, 26 (7): 1603-1610. 10.1111/jeb.12154.PubMedView ArticleGoogle Scholar
- Rouchet R, Vorburger C: Strong specificity in the interaction between parasitoids and symbiont-protected hosts. J Evol Biol. 2012, 25 (11): 2369-2375. 10.1111/j.1420-9101.2012.02608.x.PubMedView ArticleGoogle Scholar
- Moran NA: The evolution of aphid life-cycles. Annu Rev Entomol. 1992, 37: 321-348. 10.1146/annurev.en.37.010192.001541.View ArticleGoogle Scholar
- Martinez AJ, Ritter SG, Doremus MR, Russell JA, Oliver KM: Data from: Aphid-encoded variability in susceptibility to a parasitoid. Dryad Data Repository. 2014, http://dx.doi.org/10.5061/dryad.6b5f0,Google Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.