Hidden in the deadwood: Taxonomically curated barcode library reveals deep genetic divergence in Eurasian saproxylic beetles

Abstract

Saproxylic beetles are a highly diverse group of tree‐associated insects that play key roles in forest ecosystem functioning, comprising both rare primeval relicts and taxa of economic importance in timber production. Morphological identification of these beetles remains challenging due to high similarity among species‐rich taxa and a number of taxonomic specialists. While European DNA barcode reference databases have expanded in recent years, they remain dominated by western and northern populations, leaving Central and Eastern European taxa heavily underrepresented. Because previous studies have revealed pronounced east–west genetic divergence in several saproxylic beetle species, expanding barcode coverage in Central and Eastern Europe is highly necessary. Located within a biogeographical transition zone and harbouring some of Europe's last remnants of primeval forests, Poland represents a critical source of genetic data for these insects. We present a DNA barcode dataset comprising 285 morphologically identified species totalling 652 individuals, of which 261 species (557 individuals) were successfully barcoded and assigned to 274 distinct barcode index numbers (BINs), including nine species new to the BOLD database. Comparisons with GenBank and BOLD sequences revealed multiple deeply divergent lineages indicative of cryptic taxa, alongside shared haplotypes that may reflect misidentification, introgression or hybridization. This database provides a valuable resource for identifying evolutionarily significant units for conservation and may facilitate the assignment of source populations in studies of invasive pest species.