Apennine-Pyrenees disjunct distribution: An unusual biogeographic pattern revealed in flea beetles of the Longitarsus candidulus species-group (Coleoptera, Chrysomelidae)

Abstract

European mountain systems played a crucial role in shaping the distribution of species and of their genetic diversity during the Quaternary's climatic changes with the establishment of allopatric patterns across main mountain ranges. Here we investigated the evolutionary history of flea beetles of the Longitarsus candidulus species-group showing an uncommon disjunct biogeographic pattern across the Apennine and the Pyrenees. We applied a multilocus molecular approach and multispecies coalescent models to establish a phylogenetic and systematic framework for this morphologically homogeneous species-group and to estimate the time of main cladogenetic events underlying the origin of the Apennine-Pyrenees pattern. We found strong support for the monophyly of the candidulus group with a sister relationship between L. laureolae and L. leonardii endemic to the Apennine and the Pyrenees mountains respectively. The timing of speciation events in the candidulus species-group coincide with two major climatic transitions during Early and Middle Pleistocene that resulted in significant environmental changes in Europe and suggest a scenario of allopatric isolation and divergence on distinct mountain ranges. The split between the thermophilic species L. candidulus and the ancestor of the temperate species L. laureolae and L. leonardii, estimated at ~ 3 Ma during the transition from Pliocene to Pleistocene, was probably triggered by their segregation in xerophilous and temperate habitats. The speciation between L. laureolae and L. leonardii, ~ 1 Ma during the Mid-Pleistocene Transition, can be explained by the establishment of unfavorable conditions in West Alps and Central Massif underlying the onset of the Apennine-Pyrenees disjunct pattern. Finally, the strict association between members of the candidulus group and distinct Thymelaeaceae plants suggests further studies to address the hypothesis that speciation in these flea beetles might have been also associated with Pleistocene range changes of their host plants.