DOI: 10.5061/dryad.js3qj
title: Data from: Multi-modal defenses in aphids offer redundant protection and increased costs likely impeding a protective mutualism

description: 1.The pea aphid, Acyrthosiphon pisum, maintains extreme variation in
 resistance to its most common parasitoid wasp enemy, Aphidius ervi, which
 is sourced from two known mechanisms: protective bacterial symbionts, most
 commonly Hamiltonella defensa, or endogenously encoded defenses. We have
 recently found that individual aphids may employ each defense
 individually, occasionally both defenses together, or neither. 2.In field
 populations, Hamiltonella-infected aphids are found at low to moderate
 frequencies and while less is known about the frequency of resistant
 genotypes, they show up less often than susceptible genotypes in field
 collections. To better understand these patterns, we sought to compare the
 strengths and costs of both types of defense, individually and together,
 in order to elucidate the selective pressures that maintain multi-modal
 defense mechanisms or that may favor one over the other. 3.We
 experimentally infected five aphid genotypes (two lowly and three highly
 resistant), each with two symbiont strains, Hamiltonella-APSE8 (moderate
 protection) and Hamiltonella-APSE3 (high protection). This resulted in
 three sublines per genotype: uninfected, +APSE8, and +APSE3. Each of the
 fifteen total sublines was first subjected to a parasitism assay to
 determine its resistance phenotype and in a second experiment a subset
 were chosen to compare fitness (fecundity and survivorship) in presence
 and absence of parasitism. 4.In susceptible aphid genotypes, parasitized
 sublines infected with Hamiltonella generally showed increased protection
 with direct fitness benefits, but clear infection costs to fitness in the
 absence of parasitism. In resistant genotypes, Hamiltonella infection
 rarely conferred additional protection, often further reduced fecundity
 and survivorship when enemy challenged, and resulted in constitutive
 fitness costs in the absence of parasitism. We also identified strong
 aphid-genotype X symbiont-strain interactions, such that the best
 defensive strategy against parasitoids varied for each aphid genotype; one
 performed best with no protective symbionts, the others with particular
 strains of Hamiltonella. 5.This surprising variability in outcomes helps
 explain why Hamiltonella infection frequencies are often intermediate and
 do not strongly track parasitism frequencies in field populations. We also
 find that variation in endogenous traits, such as resistance, among host
 genotypes may offer redundancy and generally limit the invasion potential
 of mutualistic microbes in insects.
description: Parasitism and Fitness
 Assay DataTab 1 "Parasitism
 Assays": columns show variables that were recorded or measured and
 rows represent a single replicate of 20 parasitized aphids. Survival,
 mummification, and dual mortality were recorded 10 days after initial
 parasitism. Tab 2 "Fecundity and Survivorship": Fecundity and
 survivorship data for pea aphids that were recorded at 3-day-intervals for
 24 total days. Tab 3 "Sublethal effects": average cumulative
 fecundity of only surviving aphids from tab 2.