Variation in density, immune gene suppression, and co-infection outcomes among strains of the aphid endosymbiont Regiella insecticola

Abstract

Many insects harbor heritable beneficial microbes that influence host phenotypes. Across systems, divergent symbiont strains have been shown to establish at different densities within hosts. This genetic variation is important evolutionarily because within-host density has been linked to the costs and benefits of the symbiosis for both partners. Studying the factors shaping within-host density is therefore important to our broader understanding of host-microbe coevolution. Here we focused on different strains of Regiella insecticola, a facultative symbiont of aphids. We first demonstrated that different strains of Regiella consistently establish in pea aphids at drastically different densities. We then found that variation in density is correlated with the expression levels of two key insect immune system genes (phenoloxidase and hemocytin), with immune gene suppression correlating with higher Regiella density. We then performed an experiment where we established co-infections of a higher- and lower-density Regiella strain, and we showed that the higher-density strain is better able to persist in co-infections than the lower-density strain. Together, our results point to a potential mechanism for strain-level variation in symbiont density in this system, and further suggest that symbiont fitness may be increased by establishing at higher density within hosts. Our work highlights the importance of within-host dynamics shaping symbiont evolution.

Defensive symbiont genotype distributions are linked to parasitoid attack networks

“…Increased parasitoid diversity may not lead to increased symbiont diversity if there is a cost to resistance (Hafer-Hahmann & Vorburger 2024). Furthermore, factors such as transmission efficiency, host-symbiont compatibility, or interactions with other microbes, pathogens, or the environment, may also impact Hamiltonella diversity (Carpenter et al 2021;Dykstra et al 2014;Niepoth et al 2018;Weldon et al 2020;Goldstein et al 2023). We also did not consider genotype diversity within parasitoid species, which may influence symbiont diversity associated with an aphid species (Hafer-Hahmann & Vorburger 2020).…”

Untangling an insect virome from its endogenous viral elements

“…We screened the line for the seven species of facultative symbionts found in aphids using established PCR protocols [39,40]. For this screen, we extracted DNA using 'Bender buffer' and ethanol precipitation as in previous studies [41,42]. We then used PCR with species-specific primers [39,43] to screen for Hamiltonella defensa, Fukatsuia symbiotica (X-type), Regiella insecticola, Rickettsia sp., Ricketsiella sp., Serratia symbiotica, and Spiroplasma sp.…”