Abstract
All animals are infected by microbial partners that can be passengers or residents and influence many biological traits of their hosts. Even if important factors that structure the composition and abundance of microbial communities within and among host individuals have been recently described, such as diet, developmental stage or phylogeny, few studies have conducted cross-taxonomic comparisons, especially on host species related by trophic relationships. Here, we describe and compare the microbial communities associated with the cabbage root fly Delia radicum and its three major parasitoids: the two staphylinid beetles Aleochara bilineata and A. bipustulata and the hymenopteran parasitoid Trybliographa rapae. For each species, two populations from Western France were sampled and microbial communities were described through culture independent methods (454 pyrosequencing). Each sample harbored at least 59 to 261 different bacterial phylotypes but was strongly dominated by one or two. Microbial communities differed markedly in terms of composition and abundance, being mainly influenced by phylogenetic proximity but also geography to a minor extent. Surprisingly, despite their strong trophic interaction, parasitoids shared a very low proportion of microbial partners with their insect host. Three vertically transmitted symbionts from the genus Wolbachia, Rickettsia, and Spiroplasma were found in this study. Among them, Wolbachia and Spiroplasma were found in both the cabbage fly and at least one of its parasitoids, which could result from horizontal transfers through trophic interactions. Phylogenetic analysis showed that this hypothesis may explain some but not all cases. More work is needed to understand the dynamics of symbiotic associations within trophic network and the effect of these bacterial communities on the fitness of their hosts.
Highlights
All animals harbor microorganisms, which form a community or microbiota [1]
Bacterial richness varied between 59 Operational Taxonomic Units (OTUs) for western D. radicum (i.e. D. radicum from the ‘western’ population) and 261 OTUs for western T. rapae (Table 2)
Chao1 estimator values ranged between 182 OTUs for D. radicum and 539 OTUs for T. rapae, so that the coverage of the estimated microbial diversity ranged from 30% for western D. radicum to 63% for eastern D. radicum which is coherent with other studies on insect microbial communities
Summary
All animals harbor microorganisms, which form a community or microbiota [1]. Both in terms of frequency and diversity [2]. This diversity involves many commensal species and mutualists or pathogens, since some bacteria live as parasites while others improve nutrient assimilation or protect against pathogens and other natural enemies [3], [4], [5], [6]. Insects are the most diversified and ubiquitous group on Earth [7] and this is reflected by the diversity of their interactions with the bacteria they harbor. The interactions between insects and their microbiota have received considerable attention recently [10], [11], [12], [13], [14]
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