Tenebrionid beetle distributional patterns in Italy: multiple colonisation trajectories in a biogeographical crossroad

Placed in the centre of the Mediterranean Basin, Italy is a complex biogeographical crossroad between North Western Europe, Central Europe, Eastern Europe and North Africa. The distribution of 280 species and subspecies of tenebrionid beetles in 17 Italian natural regions was used to study the influence of climatic, spatial and historical (palaeogeographical and palaeoecological) factors on current patterns of species richness, endemism and turnover (i.e. inter-regional biogeographical differences). In accordance with the general latitudinal pattern of biodiversity in Europe, both tenebrionid richness and endemism increase southwards, in response to variations in rainfall and temperatures, as expected for thermo-xerophilic animals. Turnover was correlated with both inter-regional climatic dissimilarities and geographical distances. The importance of spatial relationships independent from climate, but consistent with palaeogeographical and palaeoecological history, was also confirmed by inter-regional relationships based on all species and endemics only. Biogeographical similarities between Italian regions and adjacent European and North African source areas showed distinct geographical patterns which reflect various dispersal trajectories. During the Pleistocene glacials, cold adapted species coming from northern areas via the Alps used the Apennines as a filter to disperse into central and southern Italy, thereafter remaining confined to high altitude areas after deglaciation. Xero-thermophilic species coming from North Africa or east Mediterranean countries colonised southern Italian regions probably in more ancient times. Islands and southern areas acted as centres of both speciation and post-glacial recolonisation.