Heritable microbial symbionts can have important effects on many aspects of their hosts’ biology. Acquisition of a novel symbiont strain can provide fitness benefits to the host, with significant ecological and evolutionary consequences. We measured barriers to horizontal transmission by artificially transferring facultative symbionts from the grain aphid, Sitobion avenae, and five other aphid species into two clonal genotypes of S. avenae. We found the symbiont Hamiltonella defensa establishes infections more easily following a transfer from the same host species and that such infections are more stable. Infection success was also higher when the introduced symbiont strain was more closely related to the strain that was originally present in the host (but which had previously been removed). There were no differences amongst successfully established symbiont strains in their effect on aphid fecundity. H. defensa did not confer protection against parasitoids in our S. avenae clones, although it often does in other aphid hosts. However, strains of the symbiont Regiella insecticola originating from two host species protected grain aphids against the pathogenic fungus Pandora neoaphidis. This study helps describe the extent to which facultative symbionts can act as a pool of adaptations that can be sampled by their eukaryote hosts.
Infection_success_data
Spreadsheet "Infection_success" summarizes the results of our attempts to introduce Hamiltonella strains from multiple donors into two recipient genotypes of Sitobion avenae.
Rows represent different host genotype - symbiont strain combinations. Columns are as follows:
***Recipient_genotype - aphid clonal genotype into which a symbiont was introduced;
***Donor_genotype - aphid clonal genotype whose symbiont-containing haemolymph was injected into the recipient;
***Donor_species - donor species, abbreviated as Siave (Sitobion avenae), Sifra (S. fragariae), Acpis (Acyrthosiphon pisum), Utsp1 (Utamphorophora sp.), Apfab (Aphis fabae);
***Intraspecific - denotes whether a particular symbiont transfer was made between clones of a single host species (S. avenae), or between different species
***Injected - the numbers of recipient aphids injected with haemolymph from the donor clone
***Surviving - the number of injected aphids which produced offspring after the 14th day from injection
***Infected - the number of injected aphids that after the 14th day from injection produced at least one infected offspring
***Stable - denotes whether after symbiont establishment in the first generation we observed cases of symbiont loss in subsequent generations
***COI_dist - p-distance (the proportion of nucleotide sites at which two sequences differ) between the recipient genotype and the donor genotype, calculated using a 641bp alignment of COI gene
***Hami_dist - p-distance between the symbiont strain infecting the donor genotype and the strain that had originally infected the recipient genotype (but was removed with antibiotics prior to the experiment) calculated using concatenation of six household genes, accD, gyrB, hrpA, murE, recJ and rpoS, of the total length of 3905bp.
Infection_success.csv
Fecundity_data
Spreadsheet "Fecundity" contains the results of the fecundity assay. We counted the number of offspring produced by isolated winged aphids, representing one of two Sitobion avenae genotypes and either facultative endosymbiont-free or hosting one of Hamiltonella or Regiella strains, during consecutive three-day intervals. In the spreadsheet, rows represent individual experimental aphids. Columns are as follows:
***Host_genotype - either Co23 or Co26; ***Symbiont_presence - 0 (no symbiont), Hami (Hamiltonella) or Reg (Regiella); ***Symbiont_genotype; ***Fecundity_16_days-from_birth - number of offspring produced by a given female within 16 days from birth.
Fecundity.csv
Parasitoid_susceptibility_data
Spreadsheet "Parasitoid_susceptibility" contains the results of the parasitoid susceptibility assay. We exposed groups of 30 aphids, representing one of two Sitobion avenae genotypes and either facultative endosymbiont-free or hosting one of Hamiltonella or Regiella strains, to females of the parasitoid wasp Aphidius ervi. After fifteen days, all aphids were checked for survival, and whether the parasitoid pupated within those aphids that died. In the spreadsheet, each row represents a replicate of approx. 30 aphids. Columns are as follows:
***Host_genotype - either Co23 or Co26; ***Symbiont_presence - 0 (no symbiont), Hami (Hamiltonella) or Reg (Regiella); ***Symbiont_genotype; ***Block - numbers denote unique experimental blocks; ***Alive - the number of aphids in a replicate that were alive at the time of the final census; ***Mummified - the number of exposed aphids which died, and within which the parasitoid pupated; ***Dead_not_mummified - the number of aphids which died over the course of the experiment, and within which the pathogen did not pupate; ***Total - the total number of aphids scored
Parasitoid_susceptibility.csv
Pathogen_susceptibility_data
Spreadsheet "Pathogen_susceptibility" contains the results of the pathogen susceptibility assay. We exposed groups of approx. 20 aphids, representing one of two Sitobion avenae genotypes and either facultative endosymbiont-free or hosting one of Hamiltonella or Regiella strains, to spores of the pathogenic fungus Pandora neoaphidis. After eight days all aphids were checked for survival, and whether the the pathogen did sporulate within those aphids that died. In the spreadsheet, each row represents a replicate of approx. 20 aphids. Columns are as follows:
***Host_genotype - either Co23 or Co26; ***Symbiont_presence - 0 (no symbiont), Hami (Hamiltonella) or Reg (Regiella); ***Symbiont_genotype; ***Treatment - aphids in most replicates were exposed to pathogen spores (treatment "Pathogen_exposure"), but we also provide data for a small number of control replicates (treatment "Control_no_pathogen"), not exposed to spores and still suffering high mortality under the experimental conditions; ***Block - dates denote unique experimental blocks; ***Alive - the number of aphids in a replicate that were alive eight days after exposure; ***Fungus_sporulated - the number of exposed aphids which died, and within which the pathogen sporulated ***Dead_not_fungus - the number of aphids which died during the course of the experiment, but which did not sporulate; ***Total - the total number of aphids scored
Pathogen_susceptibility.csv
