Are competitive interactions between aphid clones mediated by facultative endosymbionts?

Facultative bacterial endosymbionts are key components of aphid biology,
influencing host performance and ecological interactions. We investigated
how facultative endosymbionts affect competitive interactions between
aphid clones of the cereal aphid Sitobion avenae (Fabricius) in Chilean
wheat fields. We assessed the population development and life-history
traits of the two dominant genotypes (G1 and G2) under single-clone
rearing, intra- and inter-genotypic competition scenarios, with and
without the facultative endosymbiont Regiella insecticola shaping these
interactions. Our findings reveal that R. insecticola does not
significantly alter inter-genotypic competition outcomes: clone G2
consistently outcompeted G1 regardless of infection status. However, under
intra-genotypic competition, R. insecticola-infected G1 aphids
outperformed their uninfected counterparts, while the opposite trend was
observed in G2. R. insecticola influenced winged morph production and
aphid weight in a genotype-dependent manner. Aphids harbouring R.
insecticola induced less physiological stress on host plants, as evidenced
by lower root/shoot ratios. These results suggest that facultative
endosymbionts may confer clone-specific advantages, shaping aphid
performance and aphid clone-endosymbiont-plant dynamics in multifaceted
ways.