Biogeographic history of the Palearctic Pachydeminae (Coleoptera, Scarabaeoidea) inferred by dispersal-vicariance analysis

Abstract

The beetle subfamily Pachydeminae Reitter, 1902 is one of the least-known subfamilies of Melolonthidae or “leaf-chafers” (Coleoptera, Scarabaeoidea). Some species of Pachydeminae have recently been described as agricultural pests of olive trees. The Pachydeminae are distributed in all major zoogeographical regions (except Australia and India) but their distribution is very disjunct. In the Palearctic region, they are distributed across southern Eurasia from the Canary Islands to China, including southern Europe (except France and Italy), North Africa, Asia Minor, Middle East, Iran-Afghanistan, Caucasus, and Central Asia. The majority of species occur in the southwestern Palearctic, with only a few species in China. As in the rest of Melolonthidae subfamilies (Browne & Scholtz, 1999), phylogenetic relationships within the Pachydeminae are poorly resolved. Recently, Sanmartín & Martín-Piera, (2003) reviewed the systematics of the Palearctic genera, and proposed the first phylogenetic hypothesis within the subfamily. This study summarizes the conclusions of Sanmartín (1998) and Sanmartín (2003), which reconstructed the biogeographic history of the subfamily Pachydeminae in the Palearctic region using dispersalvicariance analysis (DIVA, Ronquist, 1996, 1997). This method reconstructs the ancestral distribution in a given phylogeny based on a vicariance model, while allowing dispersal and extinction to occur. Unlike other methods, DIVA does not enforce area relationships to conform to a hierarchical “area cladogram” so it can be used to reconstruct “reticulate” biogeographic scenarios. DIVA optimal reconstructions suggest that the ancestor of Pachydeminae was originally present in the south-eastern Mediterranean region, including North Africa, the Middle East, the Iranian Plateau, and the Balkans/Anatolian region. During the Oligocene-Miocene, the collision between the Arabian, African, and Eurasian Plates resulted in the appearance of consecutive dispersal barriers (e.g., the Red Sea, the Zagros Mountains). This geographic division was followed by fragmentation (vicariance) of the ancestral biota, giving rise to several disjunct genera (Pachydema Castelnau, 1832, Hemictenius Reitter, 1897). The Middle East region and the Iranian Plateau acted as centers of diversification during the evolution of the subfamily: many of the least speciose genera of Pachydeminae originated within these two regions by sympatric speciation (Otoclinius Brenske, 1896). In contrast, the presence of Pachydeminae in the Western Mediterranean region (Iberian Peninsula and southwestern Mediterranean Islands) is the result of a more recent dispersal event. The ancestor of the Iberian genera Ceramida Baraud, 1987 and Elaphocera Gené, 1836 probably dispersed from the Middle East to the Iberian Peninsula across North Africa and the Gibraltar Strait. This dispersal could have taken place during the “Messinian salinity crisis” at the end of the Miocene, when the Red Sea and the Mediterranean partially dried-up, allowing a short period of biotic dispersal between West Asia, North Africa, and the Iberian Peninsula. The subsequent evolution of Ceramida and Elaphocera seem to have involved repeated vicariance events between the East and West Mediterranean, and between the Iberian Peninsula and North Africa. In the Iberian Peninsula, the two genera are geographically segregated: most species of Ceramida are found in the southwestern region, whereas Elaphocera is generally restricted to the southeastern Iberian Peninsula.