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

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.

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

ABSTRACTHost-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 found that the ground beetle microbiome is consistent across different host food sources. We 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. Soil environment but not diet had a significant effect on bacterial diversity and composition. The three carabid species have patterns of microbial diversity similar to those previously found in other insect hosts. 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. The observed similarity of the pygidial gland secretory cell microbiome across hosts suggests the possibility that it may be a conserved community, possibly due to functional interactions related to defensive chemistry. These results provide a baseline for future studies of the role of microbes in the diversification of defensive chemical biosynthesis in carabids.

Behavioral and chemical antipredator mechanisms in ground beetles: an attempt to reconcile within a phylogenetic frame

Like other coleopterans, Carabids are recognized for the use of passive and active strategies against their enemies. They are known to produce dangerous and distasteful chemicals and to use anti-predator behaviors such crypsis/mimicry, gregariousness, intra- and interspecific helpful interactions, sound production and aposematism. While defensive chemicals have been an important element in the successful diversification of ground beetles, in many tribes of this wide adephagan family many other systems have evolved and discovered. Here we present a review on the current knowledge of the avoidance mechanisms in carabids, with a discussion of data on chemical products, morphological adaptations and behaviors used against vertebrate and invertebrate predators. The most widespread strategy is discouragement of the predators using pygidial gland secretions, but passive anti-predator strategies are also displayed as group-protecting behavior through intraspecific aggregations or communal roosting. Most adult carabids tend to be dark in color and thus less detectable, but chemically well-protected taxa use the opposite strategy, displaying bright colors related to mimicry or aposematism. In aposematic species, group-protecting behavior has probably evolved from intraspecific gregariousness into multispecies aggregations. Larval behavioral strategies are related more closely to the epigean or underground lifestyle. In surface-living larvae, cannibalism avoidance and the usage of defensive substances have been reported for Chlaeniini. In this tribe we found an interesting coincidence between a high level of toxicity/distastefulness and a complex larval behavior. Based mainly on the genus-level supertree of Beutel et al. (2008) and the phylogenetic analyses of Ober & Maddison (2008) we reconstructed the evolutionary relationships among the chemical classes isolated inside the tribes. The scenario shows that several semiochemical classes (quinone/benzoquinones, formic acid, m-cresol, methacrylic acid, isovaleric acid, ß-necrodol, benzaldehyde, etc.) found in carabids are at least in part related to their life style and habitat selection. The proposed relationship still lacks other chemical data of the missing genera/species and even if the knowledge of carabid anti-predator strategies still seems to be in the pioneer stage, future studies on carabid anti-predator behavior look very promising.

Antimicrobial activity of the pygidial gland secretion of the troglophilic ground beetleLaemostenus(Pristonychus)punctatus(Dejean, 1828) (Insecta: Coleoptera: Carabidae)

The antimicrobial activity of the pygidial gland secretion released by adult individuals of the troglophilic ground beetleLaemostenus(Pristonychus)punctatus(Dejean, 1828), applying microdilution method with the aim to detect minimal inhibitory concentration, minimal bactericidal concentration and minimal fungicidal concentration, has been investigated. In addition, morphology of the pygidial glands is observed. We have tested 16 laboratory and clinical strains of human pathogens – eight bacterial both gram-positive and gram-negative species and eight fungal species. The pygidial secretion samples have showed antimicrobial properties against all strains of treated bacteria and fungi.Micrococcus flavusproved to be more resistant compared with other bacterial strains. More significant antimicrobial properties of the secretion are observed againstEscherichia coli, which proved to be the most sensitive bacteria.Aspergillus fumigatusproved to be the most resistant, whilePenicillium ochrochloronandPenicillium verrucosumvar.cyclopiumthe most sensitive micromycetes. Commercial antibiotics Streptomycin and Ampicillin and antimycotics Ketoconazole and Bifonazole, applied as positive controls, showed higher antibacterial properties for all bacterial and fungal strains, except forP. ochrochloron, which proved to be more resistant on Ketoconazole compared with the pygidial gland secretion ofL.(P.)punctatus. Apart from the role in ecological aspects, the antimicrobial properties of the tested secretion possibly might have medical significance in the future.