Host dietary specialization and neutral assembly shape gut bacterial communities of wild dragonflies

Abstract

21Host-associated gut microbial communities can have large impacts on host ecology and 22 evolution, and are typically shaped by host taxonomy and diet. Different host species often 23 harbor distinct microbial communities, potentially because (1) host dietary specialization 24 determines microbial colonization, (2) host-specific selection acts on diet-acquired microbiota, 25and (3) a combination of both processes. While the first possibility involves passive 26 community structuring, the other two may arise from a functional association and should 27 produce stable microbial communities. However, these alternatives have rarely been tested in 28 wild host populations. We used 16S rRNA amplicon sequencing to characterize the gut 29 bacterial communities of six dragonfly species collected across multiple seasons and 30 locations. We found that variation in bacterial community composition was predominantly 31 explained by sampling season and location, and secondarily by host species. To distinguish 32 the role of host dietary specialization and host-imposed selection, we used insect-specific 33 primers to identify prey in the gut contents of three focal dragonfly species. We found that 34 these dragonflies -considered to be generalist predators -consumed distinct prey, with 35 seasonal diet variation. Together, the patterns of host dietary specialization and spatial and 36 temporal variation suggest a strong role of passive processes in shaping the gut bacterial 37 community. Indeed, the abundance and distribution of ~76% of the bacterial community 38 members were consistent with neutral community assembly. Our results contradict the 39 pervasive expectation that host-imposed selection shapes gut microbial communities, and 40 highlight the importance of joint analyses of variation in host diet and gut microbial 41 communities of natural host populations.

Fruit fly phylogeny imprints bacterial gut microbiota

“…The present results do not conform to the hypothesis that generalist species should have more diverse gut microbial communities (Deb et al, 2019), as confirmed in scavengers and omnivores (Shukla et al, 2016; Yadav et al, 2015; Yun et al, 2014). The generalist Ceratitis species had lowest gut microbial diversity (around two genus equivalents).…”

“…They depend on insect ecology, a major feature of which is host range, that is, the host plant species an insect uses. For instance, one could expect that insect species specialized on different host plants encounter different initial microbe pools and that generalist insect species encounter a more diverse set of microbes than specialist species (Deb et al, 2019). Second, host phylogeny could potentially structure insect gut microbiota through different mechanisms ranging from active filters (constrained by host development, immune function morphology, and physiology), to the sharing of similar microbe pools (through social interactions or similarity in diet; Brooks et al, 2016).…”

Antibiotics reduce bacterial load in Exaiptasia diaphana, but biofilms hinder its development as a gnotobiotic coral model

“…The copy number data were obtained by digital droplet PCR (ddPCR) to allow calculation of the bacteria/ host (B/H) cell ratio [38] for each sample. This approach has also been used to analyse bacterial load in insect samples with low mass and volume [39][40][41], with the use of a ratio accounting for differences in sample size. Primers targeting single-copy reference genes in E. diaphana and A. salina were used for host cell quantification (Table 3).…”

The red flour beetle Tribolium castaneum: A model for host-microbiome interactions

“…Insects represent one of the best-studied animals in this context, with a large number of studies showing that insect-microbiome interactions are shaped by host taxonomy, host diet, and environmental factors [ 5 – 8 ]. Importantly, insects present a spectrum of host-microbial associations ranging from transient and neutrally assembled microbiomes [ 9 – 12 ], to established relationships whereby hosts use microbial symbionts to extract dietary nutrients, digest toxins, provide essential metabolic precursors, or protect from pathogens [ 3 , 7 ]. To understand the factors that drive this spectrum of interaction strength, we need model systems where the host-microbiome interaction is suitably poised both for the evolution of a strong mutualism, as well as its breakdown.…”