Morphology, genetics and Wolbachia endosymbionts support distinctiveness of Monochamus sartor sartor and M. s. urussovii (Coleoptera: Cerambycidae)

Abstract

Monochamus sartor sartor from Central European mountain ranges and M. s. urussovii from the Eurasian boreal zone are subspecies whose taxonomic statuses have been questioned. This sawyer beetle is a natural element of spruce forests but is considered to be a timber pest in spruce plantations. In this study, different sets of data (morphology, genetics and ecology) were used to verify the taxonomic status of M. sartor across its entire range. Morphologically, not only both subspecies but also European and Asian populations of M. s. urussovii were found to be distinct. Genetic data also showed that both subspecies have distinct mitochondrial haplogroups; however, divergence between them is very weak (of ca. 1%), suggesting they split very recently, possibly at the end of the Pleistocene glaciations. Species delimitation methods gave discordant results, either rejecting the species status of M. s. sartor and M. s. urussovii (Poisson tree processes) or confirming them as distinct taxa (the multispecies coalescent model for species validation). Host plant preferences also partially differentiate the subspecies, as M. s. urussovii has a broader diet than the generally monophagous, spruce-dependent M. s. sartor. Moreover, each subspecies is infected by different strains of the intracellular bacterium Wolbachia, which could be one of the factors causing their genetic isolation, regardless of geographic isolation. Aside from broadening the basic knowledge on the taxonomy and genetics of Monochamus sartor, this study shows that any research on these sawyers needs to consider their separate phylogenetic lineages, as do any plans for population management or conservation.