Genetic diversity of the endangered saproxylic beetle Boros schneideri and preliminary insight into its associated bacterial and fungal communities

Boros schneideri is a rare and endangered saproxylic beetle associated with old, dead trees. We investigated its genetic diversity in Western Polesie, Poland, and assessed larval microbiota and mycobiota. Mitochondrial COI and 16 S rRNA, and nuclear ITS1 markers of B. schneideri were analyzed using haplotype and nucleotide diversity estimates, Bayesian phylogenetic analyses, and median-joining networks. COI sequences were additionally compared with records from Poland, Finland, and Mongolia. Both mitochondrial and nuclear datasets revealed high haplotype diversity and moderate nucleotide diversity, while phylogenetic trees and haplotype networks showed shallow relationships without distinct, well-supported geographic lineages. Shared COI haplotypes occurred among geographically distant populations. Negative Tajima’s D and Fu’s Fs values, together with the diversity pattern, were consistent with a possible recent demographic expansion. No Wolbachia infection was detected. High-throughput sequencing targeting the bacterial 16 S rRNA V3–V4 region and fungal ITS1 revealed diverse bacterial communities in 11 larvae, dominated by Proteobacteria, particularly Burkholderiaceae and Yersiniaceae. Preliminary mycobiota profiling of one larva identified predominantly Ascomycota, including Ophiostoma , previously suggested as a potential food resource. Despite limited sampling, these findings provide a baseline for understanding the genetic and microbial diversity of B. schneideri and support integrating population genetics and microbiome research into future conservation studies.