Colour pattern and DNA-barcoding reveal a wide distribution of the insular endemic bumble bee Bombus xanthopus in the Tuscan Archipelago

Insular ecosystems, due to their isolation from the mainland and limited areas, are often endemism hotspots. However, the same factors that drive high endemicity also make islands vulnerable to anthropogenic pressure and thus to biodiversity loss. We focused on a taxon of emerging conservation interest, the insular endemic bumble bee Bombus xanthopus, in the Tuscan Archipelago. It was formerly known to occur in Corsica and on two of seven islands of the archipelago where it hybridises with the widely distributed Bombus terrestris. We conducted distributional, morphological and molecular analyses of B. terrestris-xanthopus populations across the seven islands to update the distribution of B. xanthopus and characterise its morphological and molecular distinctiveness from B. terrestris. We found that B. xanthopus and intermediate colour morphs occur more widely than previously reported, being present across the entire archipelago. Significant associations between typical morphs of both B. xanthopus and B. terrestris and COI haplogroups highlight the reliability of both markers in identifying the two taxa (more than 80% of individuals had concordant colour patterns and genetic markers). Despite evidence of hybridisation, our findings indicate that complete discordance between morphological and molecular markers is uncommon. Moreover, most intermediate individuals (12 out of 14) carried B. xanthopus haplotypes. The absence of B. xanthopus from mainland Tuscany suggests possible relictualism phenomena. This study provides a comprehensive update on the distribution and genetic structure of B. xanthopus. Our results show that targeted efforts are essential to protect this unique component of the Tuscan Archipelago pollinator community. As these islands represent a biodiversity hotspot, where evolutionary processes and conservation challenges intersect, we encourage national park authorities and policymakers to continue prioritising the protection of wild pollinators of the Archipelago in their conservation plans.