Persistence of the ground beetle (Coleoptera: Carabidae) microbiome to diet manipulation

Abstract

Host-associated microbiomes can play important roles in the ecology and evolution of their insect hosts, but bacterial diversity in many insect groups remains poorly understood. Here we examine the relationship between host environment, host traits, and microbial diversity in three species in the ground beetle family (Coleoptera: Carabidae), a group of roughly 40,000 species that synthesize a wide diversity of defensive compounds. This study used 16S amplicon sequencing to profile three species that are phylogenetically distantly related, trophically distinct, and whose defensive chemical secretions differ: Anisodactylus similis LeConte, 1851, Pterostichus serripes (LeConte, 1875), and Brachinus elongatulus Chaudoir, 1876. Wild-caught beetles were compared to individuals maintained in the lab for two weeks on carnivorous, herbivorous, or starvation diets (n = 3 beetles for each species-diet combination). Metagenomic samples from two highly active tissue types—guts, and pygidial gland secretory cells (which produce defensive compounds)—were processed and sequenced separately from those of the remaining body. Bacterial composition and diversity of these ground beetles were largely resilient to controlled changes to host diet. Different tissues within the same beetle harbor unique microbial communities, and secretory cells in particular were remarkably similar across species. We also found that these three carabid species have patterns of microbial diversity similar to those previously found in carabid beetles. These results provide a baseline for future studies of the role of microbes in the diversification of carabids.

Patterns of Microbiome Composition Vary Across Spatial Scales in a Specialist Insect

“…Commonly occurring bacteria (i.e., those represented in 50% of samples) totaled seven for both D. virgifera virgifera and D. barberi , with four being shared between the two species. This is consistent with other insects which host facultative microbes with high variation between individuals ( Blankenchip et al, 2018 ; Hammer et al, 2020 ; Silver et al, 2021 ). The number of shared taxa between WCR and NCR was relatively small (~12%) but accounted for a high amount of the total sequences within the communities (~90%).…”

The ground beetle Pseudoophonus rufipes gut microbiome is influenced by the farm management system

“…Proteobacteria is usually among the dominant phyla in insects 37 including the other Carabidae species in which the gut microbiota has been studied 21 , 38 , 39 . Therefore, the differences we have found in the beetles collected at the organic management fields is in line with the observations that correlate the insect gut microbiota shaping to the environment 40 and perhaps to pathogen spread on food sources 41 .…”

“…The differences outlined in the carabids microbiome may also be influenced by the high number of plant species involved in crop rotation in ORG (n = 9) compared to CNV (n = 3) (Table 1 ). However, according to Silver et al 38 , different diets (from carnivorous to herbivorous) may have minor effects on gut microbial community of ground beetles, at least in a short-term diet. This makes it unlikely that plant diversity could cause the microbiota to diverge so much in the two environments.…”

“…metabolism of amino acids, lipids and carbohydrates). Since bacterial composition and diversity of Carabids have been seen largely resilient to controlled changes to host diet 38 , an increasing of some taxa in conventional (including Enterobacteriaceae) could be ascribed to stressors like pesticide use. Changes in the microbiota communities of the ground beetle P. melas italicus after exposition to an herbicide 21 was likely the cause of variations of the antagonistic interaction among different bacteria with different metabolic requirements, including the increasing of facultative pathogens.…”

Molecular phylogeny and revision of species groups of Nearctic bombardier beetles (Carabidae, Brachininae, Brachinus ( Neobrachinus))

“… Brachinus are abundant predators and scavengers in their communities, they offer other carabids (e.g., certain species of Agonum Bonelli, Chlaenius Bonelli, and Platynus Bonelli) well-protected spaces in multispecies aggregations ( Schaller et al 2018 ), and they have the potential to sustainably manage pest populations in agroecosystems ( Scaccini et al 2020 ). Previous research has also examined their larval development ( Erwin 1967 ; Juliano 1984 ; Juliano 1985 ; Saska and Honek 2004 ), aggregation behaviors ( Brandmayr et al 2006 ; Schaller et al 2018 ), and microbiome ( McManus et al 2018 ; Silver et al 2021 ).…”