Climate Relicts: Asian Scorpion Family Pseudochactidae Survived Miocene Aridification in Caves of the Annamite Mountains

Southeast Asia is a hotspot of karst systems in the tropics and many relictual taxa have been documented in caves across the region. The ancient, relictual scorpion family Pseudochactidae Gromov 1998 has a disjunct distribution and includes two hypogean subfamilies from caves in the Khammouan-Phong Nha-K Bàng Karst in the northern Annamite (Trưng Sơn) Mountains of Laos and Vietnam, and one epigean subfamily from Central Asia. A recent revision identified six species in the family; however, how these taxa dispersed and diversified into Southeast Asian cave systems has not been tested. In the present contribution, the phylogeny of Pseudochactidae is reconstructed using three mitochondrial and three nuclear markers and 140 morphological characters, divergence time and ancestral range estimation analyses are conducted, and the evolution of troglomorphic characters is investigated. Results confirm a previous hypothesis that Pseudochactidae originated in Eurasia, most likely near the Tajik block in the Carboniferous, supporting the ‘Out of Eurasia’ hypothesis and contradicting the ‘Eurogondwana’ and ‘Out of India’ hypotheses for the origin of Southeast Asian scorpions. Pseudochactidae dispersed across Southeast Asia after the collision of the Cimmerian continent and Indochina with Eurasia in the Late Jurassic. Colonization of Southeast Asian caves began in the Late Cretaceous and was completed by the Miocene. The onset of aridification in Southeast Asia during the Late Miocene resulted in the extinction of epigean Pseudochactidae, whereas hypogean members of the family likely survived within caves in the limestone massifs of the Annamite Mountains, supporting the ‘Climate Relict’ hypothesis.