Mediterranean lineage endemism, cold-adapted palaeodemographic dynamics and recent changes in population size in two solitary bees of the genus Anthophora

Anthophora plumipes is a solitary bee species common in Europe, Northern Africa, and the Middle East. Its sibling species A. villosula, which inhabits Eastern Asia, was recently introduced to the USA from Japan and has become naturalized there. The phylogeographic pattern in both species is unknown. Therefore, they are appropriate models for a phylogeographic study addressing overall genetic structure and colonization history. Analyses based on 11 microsatellite loci and a 727-bp cytochrome oxidase I (COI) sequence in samples from 41 localities, including the USA and Japan, revealed the presence of divergent clusters with strong geographic patterns. Both nuclear and mitochondrial markers show a significant genetic differentiation of A. villosula from A. plumipes, supporting their status as separate species. Several unique and divergent COI haplotypes in Spain, Greece and Israel indicate a high level of Mediterranean endemism, likely resulting from post-glacial areal contraction and fragmentation. A Bayesian skyline plot analysis suggests palaeodemographic dynamics typical of cold-adapted species - a stable effective population size during the ice age and its accelerated decrease after the glacial maximum. Recently, population sizes have increased and stabilized with land urbanization. A Bayesian clustering analysis of the microsatellite data only partially supported the Mediterranean COI groups, likely suggesting recent admixture of formerly isolated populations. Similarly, the British localities formed a separate cluster based on microsatellite markers, which was not supported by mitochondrial DNA. Analyses based on an isolation with migration model revealed a low effective population size for the British population and suggested asymmetric gene flow, primarily from continental Western Europe to the British Isles.