Spatio-temporal diversification pattern of Brinckia (Coleoptera: Tenebrionidae) in the Namib coastal belt

Abstract

Beetles of the family Tenebrionidae, particularly those of the subfamily Pimeliinae, are highly diverse and abundant in desert ecosystems. The sensitivity of the many wingless species to geographical and ecological isolation makes them ideal candidates for studying effects of climatological and/or geophysical changes on organismal diversity. Our study focuses on Brinckia, the only genus of the subtribe Hypomelina adapted to coastal sand dune hummocks (nabkhas) and restricted to that environment along the Namib Desert and the transitional Namib south of the Orange River. Today, Brinckia appear to be common along the coast, albeit with different species, wherever the absence of shifting sand dunes enables the beach hummocks to form, mainly around Salsola and Zygophyllum species. Therefore, past diversification can probably be directly attributed to temporary extinctions of this habitat in certain coastal regions. The presumed center of origin and diversification of Brinckia is on the Gariep Karoo coastline between Port Nolloth and Lüderitz. Our molecular phylogenetic analysis suggests that the first split within Brinckia occurred ∼2.3 Ma, i.e., relatively recently, and may be associated with aridification that occurred at that time due to global climate change. However, subsequent speciation is more likely the result of the emergence of extensive dune fields, which may have been responsible for temporary habitat degradation in the supralittoral zone. More recent, recurrent and ongoing diversification since the mid-Pleistocene transition, as observed for tenebrionids along the coast of the Atacama and Peruvian deserts, is not typical of Brinckia and supports the stability of their coastal habitat despite glacial climate oscillations.