Protection against a fungal pathogen conferred by the aphid facultative endosymbionts Rickettsia and Spiroplasma is expressed in multiple host genotypes and species and is not influenced by co‐infection with another symbiont

Abstract

Many insects harbour facultative endosymbiotic bacteria, often more than one type at a time. These symbionts can have major effects on their hosts' biology, which may be modulated by the presence of other symbiont species and by the host's genetic background. We investigated these effects by transferring two sets of facultative endosymbionts (one Hamiltonella and Rickettsia, the other Hamiltonella and Spiroplasma) from naturally doubleinfected pea aphid hosts into five novel host genotypes of two aphid species. The symbionts were transferred either together or separately. We then measured aphid fecundity and susceptibility to an entomopathogenic fungus. The pathogen-protective phenotype conferred by the symbionts Rickettsia and Spiroplasma varied among host genotypes, but was not influenced by co-infection with Hamiltonella. Fecundity varied across single and double infections and between symbiont types, aphid genotypes and species. Some host genotypes benefit from harbouring more than one symbiont type.

The extended phenotypes of marine symbioses: ecological and evolutionary consequences of intraspecific genetic diversity in coral–algal associations

“…Among genetically identical host clones of pea aphids, pathogen resistance was conferred to different degrees by distinct strains of a facultative bacterial symbiont species (Lukasik et al, 2013b). Conversely, host pathogen resistance and fecundity varied among host genotypes associating with a clonal symbiont (Lukasik et al, 2013a). These examples highlight that intraspecific diversity among holobiont partners can be high and drive complex interactive effects that mediate holobiont fitness in multiple ways.…”

“…In pea aphid studies, symbiont genotype affected the extent of pathogen sporulation in dead hosts, which likely altered community dynamics by limiting or expanding the exposure of other aphids to the fungus (Lukasik et al, 2013a,b). In the Pacific Northwest, locally derived leaf litter from red alder trees ( Alnus rubra ) decomposed more rapidly than litter derived from trees at other riparian zones, indicating intraspecific variants might drive community-level changes to ecosystem flux (Jackrel and Wootton, 2013).…”

The Facultative Symbiont Rickettsia Protects an Invasive Whitefly against Entomopathogenic Pseudomonas syringae Strains

“…nr. bellii strain protects pea aphids (Acyrthosiphon pisum) against a fungal pathogen (11,18). Laboratory assays that consistently show the better performance of R ϩ whiteflies in the absence of any known pathogens may make defense against pathogens unlikely to be the only role for the symbiont in whiteflies (16), but defense could contribute to the success of infected whiteflies in areas where pathogens are common.…”

“…For example, the secondary symbiont Hamiltonella defensa provides protection against a parasitoid wasp to pea aphids and may be common in pea aphid populations that experience high levels of parasitism (4,6). Laboratory studies have shown that symbionts can also play a major role in protecting their insect hosts from microbial pathogens (11,12). Insects regularly interact with numerous environmental bacteria, some of which are likely to be specialists or opportunistic pathogens and thus possibly influence insect fitness and the dynamics of defensive symbionts.…”

Heat Stress Affects Facultative Symbiont-Mediated Protection from a Parasitoid Wasp

“…The presence of a second symbiont potentially changes the phenotypic effect seen in a single infection, possibly because two symbionts consume more resources [22]. Spiroplasma in aphids can confer resistance to a fungal pathogen [32,33] and can affect the host’s fecundity [33–35] particularly in coinfections with H . defensa [33].…”