Saproxylic Insights: Unveiling Gut Microbial Dynamics in Forest Floor Invertebrates and Their Frass in the Tallaganda Region, NSW

Abstract

Host-microbe associations have been, and continue to be, an area of great interest. Even within a well-defined and well-studied gut microbial community, little attention has been paid to how the dynamics of the host's gut environment may undergo shifts, potentially exhibiting concurrent variations along the spectrum of microbial independence within that particular microenvironment, ranging from loose and opportunistic host-microbe associations at one end to intimate and specific associations at the other. This study explored factors influencing gut microbial assembly and diversity among forest floor invertebrate hosts: saproxylic velvet worms, saprophagous wood cockroaches, funnel web spiders, and their immediate environment, the frass. All individuals used in this study were found in the Tallaganda Region of New South Wales, Australia. This study utilized the V4-V5 region of the 16S rRNA gene sequences to characterize the gut microbial structure and composition of the hosts in the wild, and in velvet worms along a gradient of semi-isolated refugia. A six-week feed experiment on velvet worms, wood cockroaches, huntsman and funnel web spiders showed higher gut microbial diversity in wood cockroaches than in velvet worms and spiders combined. Moreover, the microbiome of the fed groups seemed to be unaffected by feeding regimes, which included feeding or fasting. Low microbial diversity and highly variable gut microbial communities were observed across all velvet worms, funnel web, and huntsman spiders' gut samples. The core bacterial phyla across all hosts' gut samples were Proteobacteria, Actinobacteria and Firmicutes, with prevalence ranging from 40 -95 %. Interestingly, all these three taxa were also found in frass samples. In summary, combined with the results of the feeding experiments, while the core microbiome has been observed in at least 40% of the samples of interest, the likelihood of a persistent core microbial population in these species is rather low, in contrast to the wood cockroach, which appears to have a well-established community of gut microbes. These findings suggest additional research is essential to understanding the complexities of gut microbial communities and highlight the hosts' ability to dynamically engage with transient microbial communities within their direct surroundings, dead wood microhabitats. This nuanced understanding provides an ecological insight into the host-gut microbial associations and the dead wood microenvironment. It contributes to the ongoing discourse on the ecological dynamics of host-microbe associations, emphasizing the contextual significance of microbial independence along a spectrum of host-microbe interactions. These findings illuminate the complexities inherent in the interplay between hosts and their microbial communities, offering valuable insights into dead wood microhabitats. Show more