Gut bacteria reflect the adaptation of Diestrammena japanica (Orthoptera: Rhaphidophoridae) to the cave

Abstract

The gut microbiota is essential for the nutrition, growth, and adaptation of the host. Diestrammena japanica, a scavenger that provides energy to the cave ecosystem, is a keystone species in the karst cave in China. It inhabits every region of the cave, regardless of the amount of light. However, its morphology is dependent on the intensity of light. Whether the gut bacteria reflect its adaptation to the cave environment remains unknown. In this research, D. japanica was collected from the light region, weak light region, and dark region of three karst caves. The gut bacterial features of these individuals, including composition, diversity, potential metabolism function, and the co-occurrence network of their gut microbiota, were investigated based on 16S rRNA gene deep sequencing assay. The residues of amino acids in the ingluvies were also evaluated. In addition, we explored the contribution of gut bacteria to the cave adaptation of D. japanica from three various light zones. Findings showed that gut bacteria were made up of 245 operational taxonomic units (OTUs) from nine phyla, with Firmicutes being the most common phylum. Although the composition and diversity of the gut bacterial community of D. japanica were not significantly different among the three light regions, bacterial groups may serve different functions for D. japanica in differing light strengths. D. japanica has a lower rate of metabolism in cave habitats than in light regions. We infer that the majority of gut bacteria are likely engaged in nutrition and supplied D. japanica with essential amino acids. In addition, gut bacteria may play a role in adapting D. japanica's body size. Unveiling the features of the gut bacterial community of D. japanica would shed light on exploring the roles of gut bacteria in adapting hosts to karst cave environments.

Keywords: 16S rRNA gene sequencing; adaptation; amino acid metabolism; cave; gut microbiota; insect; light strength.

FIGURE 1

Gut bacteria dynamics among different light-strength regions in Diestrammena japanica. (A) Morphology of D. japanica from different light-strength regions. (B) Rarefaction curves generated from randomly subsampled data sets with the same number of 16S rRNA gene deep sequencing. (C) Relative abundance of gut bacteria at the phylum level. (D) Relative abundance of the top 35 abundance genera gut bacteria, the color scales display the bacterial relative abundance (log10 transformed). L, light region; WL, weak light region; D, dark region. These labels are the same as in the other figures.

FIGURE 2

Gut bacterial community dynamics among different light-strength regions in D. japanica. (A) Community diversity measured by the Shannon index and Simpson index. (B) Overlap of OTUs from different light-strength regions. (C) Principal component analysis showed gut bacteria were clustered into two groups according to light strengths, based on the Adonis testing result (R = 0.3457, p = 0.049); the different colors show different groups with the boundaries of the 95% confidence ellipses. The red represents the species from weak light and dark regions.

FIGURE 3

Co-occurrence network analysis of gut bacteria community in D. japanica. The size of the node represents the relative abundance. Positive interaction, gray line; negative interaction, red line.

FIGURE 4

Relative abundance of gut bacterial function classification, inferred from PICRUSt analysis prediction.

FIGURE 5

Abundance of metabolism pathway (A) and titer of amino acids (B), the three letter codes represent the different amino acids, following the general amino acid code list, and the color scales indicate the abundances of metabolism pathways and amino acids.