Genotype-by-genotype interactions demonstrate the existence of variation upon which selection acts in host-parasite systems at respective resistance and infection loci. These interactions can potentially be modified by environmental factors, which would entail that different genotypes are selected under different environmental conditions. In the current study, we checked for a G x G x E interaction in the context of average temperature and the genotypes of asexual lines of the endoparasitoid wasp Lysiphlebus fabarum and isolates of Hamiltonella defensa, a protective secondary endosymbiont of the wasp's host, the black bean aphid Aphis fabae. We exposed genetically identical aphids harbouring different isolates of H. defensa to three asexual lines of the parasitoid and measured parasitism success under three different temperatures (15°C, 22°C and 29°C). While there was clear evidence for increased susceptibility to parasitoids at the highest average temperature and a strong G x G interaction between the host's symbionts and the parasitoids, no modifying effect of temperature, that is no significant G x G x E interaction, was detected. This robustness of the observed specificity suggests that the relative fitness of different parasitoid genotypes on hosts protected by particular symbionts remains uncomplicated by spatial or temporal variation in temperature, which should facilitate biological control strategies.

Average temperature experiment - Cayetano & Vorburger 2013'temp' lists the average temperatures in degrees Celsius that the replicates in the study were exposed to. 'day' means the day on which the replicates were exposed to processed. The experiment had a block design, with four blocks exposed to the heat treatments on the first day, and three blocks on the second. 'a_line' lists the aphid sublines, desigated as either '407' (an uninfected line), or some other number that designates an endosymbiont isolate with which the aphids in that subline are infected (eg. '402' means that the subline is infected in with endodymbiont 402). 'n_exposed' means the number of juvenile aphids exposed to the wasps (this variable is called 'colony size' in the manuscript). 'ang_p_mumm' is the arcsine square root tranformed proportion of aphids mummified. RES_1 are the residuals resulting from a full factorial general linear model with n_exposed as the covariate, ang_p_mumm' as the response variable and 'temp', 'a_line' and 'p_line' (parasitoid lines) as the fixed factors.