Phylogeography of the endangered saproxylic beetle Rosalia longicorn, Rosalia alpina (Coleoptera, Cerambycidae), corresponds with its main host, the European beech (Fagus sylvatica, Fagaceae)

Aim The Rosalia longicorn (Rosalia alpina) is an internationally protected icon of biodiversity associated with old trees and dead wood. Although the beetle regularly exploits several marginal hosts, its preferred main host is European beech (Fagus sylvatica s.l.). Moreover, the geographical ranges of R. alpina and beech closely overlap. To assess whether their spatial association is mirrored in the genetic patterns of both species, we investigated the phylogeography of Rosalia alpina over its entire geographical range and compared it with the known genetic patterns of its hosts. Location Methods Europe and western Asia. Using both mitochondrial (COI) and nuclear (14 microsatellite loci) markers, we analysed 148 (444, respectively) individuals from 31 (30, respectively) sites. We constructed a Bayesian Inference tree and a haplotype network, calculated the spatial analysis of molecular variance and assessed the population structure of our dataset using two Bayesian clustering methods (STRUCTURE and BAPS). Results Main conclusions Mitochondrial markers suggested existence of five clades in R. alpina populations. Two of them were endemic to the Italian mainland, one to Sicily, and another to southern Turkey. The remaining clade probably originated in the Balkans and colonized the rest of the species' range. Nuclear markers supported this division. They also suggested two main recolonization routes from the Balkans; one heading north and then both west and east, the second expanding eastwards as far as the Caucasus. The observed genetic patterns were largely congruent with those of European beech. The results of both markers were mostly congruent, suggesting at least four potential refugia for R. alpina located in the southernmost parts of its geographical range. Its populations from a large part of Europe and western Asia, however, were genetically poor, dominated by a single haplotype. Phylogeographies of the beetle and its main host seem to be tightly matched, reflecting their common history.