Pleistocene connection between the Nearctic Mediterranean and desert regions in the Sphaeropthalma unicolor species-complex (Hymenoptera: Mutillidae)

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Abstract. 1. While a growing number of studies have been published investigating the history of diversification of desert-adapted taxa, little work has been done on the history of diversification of Mediterranean-adapted and related desert-adapted species. Here, we investigate the historical biogeographical patterns within and among species of the Sphaeropthalma unicolor species-complex (Hymenoptera: Mutillidae) to determine if the diversification leading to the close relationship between the desert-adapted and Mediterranean-adapted species resulted from late Neogene uplift events or Pleistocene climatic fluctuations. 2. Phylogenetic reconstructions showed each of the three species in the S. unicolor species-complex forming a distinct, well-supported clade with little population-level structuring within the Mediterranean-adapted S. unicolor (Cresson) and more structuring among desert-adapted Sphaeropthalma mendica (Blake) populations. Molecular dating analyses indicated the split between Sphaeropthalma angulifera and the other two species occurring in the late Neogene and the split between S. unicolor and S. mendica occurring in the early Pleistocene. Ecological Niche Models projected onto Pleistocene climate surfaces indicated that the glacial and interglacial periods caused expansion and contraction of suitable habitat for each species. 3. Both late Neogene and early Pleistocene events were influential in the diversification of the S. unicolor species-complex, but Pleistocene climatic fluctuations seem to have been responsible for the split between the Mediterranean-adapted species and the desert-adapted species. While the majority of species-level diversification events in arid-adapted taxa seem to have been driven by Neogene vicariant events, Pleistocene climatic changes apparently did drive diversification in some taxa.