Variation inMelitaea cinxiagut microbiota is phylogenetically highly structured but only mildly driven by host plant microbiota, sex or parasitism

Abstract

Originality-Significance StatementThe factors contributing to the assembly of microbiota in animals are extremely complex, and thus a comprehensive understanding of the mechanisms shaping host-associated microbial communities in natural ecosystems requires extensive ecological studies and appropriate statistical methods. In this study, we investigated the bacterial microbiota associated with the caterpillars of the Glanville fritillary (Melitaea cinxia), which is a long-term-studied ecological model system. We assessed the structure of variation in both occurrence and abundance of gut microbial communities of individuals collected in the wild with joint-species modelling, with the aim to relate the microbial community structure with multiple potentially impacting covariates: host plant microbiota and metabolites, hosts’ sex, potential parasitoid infection, and family structure. These covariates exhibited substantial correlation with multiple microbial taxa’s occurrences, which correlations were consistent for phylogenetically related groups of taxa, but varied across the whole microbial community; on the contrary, only few correlations were found with taxa’s abundances. The dominating co-occurrence pattern of microbiota assembly, which effectively split caterpillar individuals into two distinct groups, was, however, unrelated to any of the considered covariates.SummaryUnderstanding of what ecological factors shape intraspecific variation of insect microbiota is still relatively poor. In Lepidopteran caterpillars, microbiota is assumed to be mainly composed of transient bacterial symbionts acquired from the host plant. We sampled Glanville fritillary (Melitaea cinxia) caterpillars from natural populations to describe the microbiome and to identify potential factors that determine the structure of the microbial community, including the sex of the host, the impact of parasitoid infection, and the possible link between host plant and caterpillar microbiota. Our results demonstrate high variability of microbiota composition even among caterpillars that shared the same host plant individual. The observed variation in microbiota composition is partially attributed to the measured properties of the host or its plant microbial and chemical composition, and is aligned with microbial phylogenetic structure, with related taxa exhibiting similar patterns. However, the prevailing part of the observed variation was not associated with any of the assessed characteristics, although it followed a pronounced segregation structure: in some caterpillars the microbial communities were dominated by several related Enterobacteriaceae taxa, while in others these taxa were absent. Our results challenge previous findings that the host plant properties are the major drivers of microbiota communities of insect herbivores.

Influence of Diet, Sex, and Viral Infections on the Gut Microbiota Composition of Spodoptera exigua Caterpillars

“…So, the variability observed among the different greenhouses could be attributed to differences in foliar microbiota of each pepper plant and the greenhouse soil microbiota in which the caterpillars were collected. This explanation is also supported by previous studies in which the larval gut bacteria did not totally correspond with dietary associated leaf bacteria (Whitaker et al, 2016;Hammer et al, 2017;Minard et al, 2019). Thus, the authors suggested larval gut microbiota is composed of transient bacteria instead of resident microbiota, due to the intrinsic insect gut physiology, such as their high pH, simple tube structure, and rapid digestion that prevent gut colonization by bacterial uptake with food (Hammer et al, 2017).…”

“…In addition, previous Lepidoptera studies revealed apparent contradictions with respect to diet influence on gut microbiota. Some studies claimed diet significantly influenced lepidopteran gut microbiota composition (Yun et al, 2014;Berman et al, 2018;Phalnikar et al, 2018;Jones et al, 2019), whereas other authors reported diet had little or no effect on microbiota (Whitaker et al, 2016;Chaturvedi et al, 2017;Minard et al, 2019). This apparent contradiction seems to reveal the lack of caterpillar specific gut microbiota as reported by Hammer et al (2017).…”

“…Spodoptera litorallis adults differ in their microbiota community composition, since female microbiota is composed mainly of Enterococcus, Klebsiella, and Pantoea genera, while the male microbiota is dominated by Klebsiella (Chen et al, 2016). van Schooten et al (2018) also reported significant abundance differences between sexes in several Heliconius species, but only for 13 rare OTUs, as similarly occurs for a few Melitaea cinxia larvae taxa (Minard et al, 2019). Recent S. exigua studies by Gao et al (2019) described the absence of differences in microbiota composition between male and female adults.…”

Modelling spatial patterns in host‐associated microbial communities

“…While the computational costs of the earlier JSDMs were intractable for microbial data, it is now possible to handle hundreds of taxa and samples in a reasonable time (Tikhonov et al ., 2020a; Tikhonov et al ., 2020b). A few recent studies applied JSDMs to investigate spatial patterns in microbiota (Björk et al ., 2018; Aivelo et al ., 2019; Minard et al ., 2019). In particular, a recent study adapted JSDMs to microbiota by incorporating host phylogeny and traits and illustrated this development on bird and sponge microbiota (Björk et al ., 2018).…”

“…This study demonstrates the use of JSDMs to partition variance between spatial effects and host‐related factors and to obtain co‐occurrence networks. A study conducted on caterpillar microbiota revealed phylogenetic structuring in the communities, with related microbial taxa exhibiting similar patterns (Minard et al ., 2019). The communities displayed high variation between individual caterpillars, on which neither the host‐ and host plant‐related factors nor spatial structure appeared to have significant influence.…”