Molecular biogeography of Mediterranean and southern African disjunctions as exemplified by pollen beetles of the Meligethes planiusculus species-group and related taxa (Coleoptera: Nitidulidae; Meligethinae)

We investigated the apparent disjunction expressed in two related assemblages of species of the genus Meligethes, i.e. M. fruticola and its allies in the Cape region of South Africa and the M. planiusculus group in the Mediterranean region. We also inferred possible dynamics in the radiation of the Meligethes planiusculus complex within Macaronesia utilizing morphological, molecular and bionomical data, exploring potential historical and palaeoecological scenarios regulated by a molecular clock dating system. We reconstructed phylogenetic relationships of the M. planiusculus complex and of related Mediterranean (M. tristis), tropical (M. scotti) and southern African (M. chevrolati, M. conformis, and M. fruticola) species, using COI mitochondrial gene sequences. Phylogenetic reconstructions support an unambiguous distinction of two major clades grouping European-Mediterranean M. canariensis, M. isoplexidis andM. planiusculus specimens in one clade and the South-African specimens related to M. fruticola in another. Molecular markers suggested that the European-Mediterranean taxon M. tristis is unambiguously more distantly related to the partly sympatric M. canariensis, M. isoplexidis and M. planiusculus, than to the geographically isolated Southern African taxon, M. fruticola. However, morphological data revealed that M. tristis is more closely related to M. planiusculus and its allies while occupying a position internal to the M. planiusculus species group, but external to the M. planiusculus complex. Results of divergence estimation analyses suggest a splitting between ancestors of the European-Mediterranean species of the M. planiusculus complex and that of the African species M. fruticola at ~21-23 MYA. Molecular results also demonstrated that the remaining Afrotropical species are more related to the M. planiusculus and M. fruticola complexes than to M. tristis. This evidence clearly indicates that the Holarctic M. planiusculus group represents a paraphyletic assemblage with heterochronic Afrotropical origin. The estimated times of divergence supports evidence from other researchers of an ‘Arid Corridor’, or of a ‘Central or Eastern High Africa Corridor’, which connected several times in the last twenty MY the European-Mediterranean and eastern/southern African areas, and facilitated species migration northwards and southwards. The dynamics of the Meligethes planiusculus complex radiation in Macaronesia apparently followed a contradictory biogeographical scenario than the sequence of events recently hypothesized for their host-plants (Echium, Boraginaceae).