Bacterial symbionts can freely mix-and-match phenotypes which they confer on their insect hosts
Microbial symbionts commonly confer important modifications on their insect hosts. We tested this using pea aphids (Acyrthosiphon pisum) and their facultative bacterial symbiont Spiroplasma.
Image description: Left panel: Pea aphid (Acyrthosiphon pisum) attacked by parasitic wasp Aphidius ervi. Right panel: Pea aphid infected by fungal pathogen Pandora neoaphidis.
Microbial symbionts commonly confer important modifications on their hosts. These modified phenotypes improve transmission of the symbiont to next generation and can have a positive effect on their host (as is the case with conferred protection from parasitic wasps or fungal pathogens), or negative consequences (when manipulating reproduction). Typically, only one phenotype is studied and we therefore don’t know whether the phenotypes co-vary positively, negatively, or can be independently mixed. We tested this using pea aphids (Acyrthosiphon pisum) and their facultative bacterial symbiont Spiroplasma. We experimentally moved 11 different strains of Spiroplasma into the same aphid clonal background to filter out the effect of host genotype and tested the aphids for the phenotypes. We found that each phenotype is highly variable and that there is no correlation, positive or negative, between the strength of different phenotypes. The phenotypes also cannot be predicted by historical relatedness of the symbiont strains, which means that transitions between phenotypes are happening rapidly. We conclude that multiple symbiont-mediated phenotypes can evolve independently from one another without trade-offs between them.
McLean A., Hrček J., Parker B., Mathé-Hubert H., Kaech H., Paine C., Godfray, H. (2020) Multiple phenotypes conferred by a single insect symbiont are independent. Proceedings of the Royal Society B 287: 20200562.