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Stephanie Loria and Lorenzo Prendini published last fall an interesting article on the evolution and diversification of the Asian forest scorpions (subfamily Heterometrinae of Scorpionidae). There are several hypothesis for explaining explain patterns of distribution among Southeast Asian animal taxa. The authors concludes that the "out of India" hypothesis is the most probable for the Asian forest scorpion. What does this mean:
1. Scorpionid taxa originated in Africa and the Heterometrinae diverged from other Scorpionidae on the African continent after the Indian subcontinent became separated in the Cretaceous period.
2. A mass extinction event with subsequent environmental stress restricted Heterometrinae to refugia in southern India (the Western Ghats) and Sri Lanka (the Central Highlands).
3. Heterometrinae dispersed to Southeast Asia three times during India’s collision with Eurasia ("Out of India").
4. Indian Heterometrinae, confined to southern India and Sri Lanka during the mass extinction mentioned above, recolonized the Deccan Plateau and northern India, diversifying into new, more arid habitats after environmental conditions stabilized.
This article confirms previous suggestions that the ‘Out of India’ hypothesis best explains the origin of Southeast Asian Heterometrinae, given their sister-group relationship with the African Pandininae, and the absence of Heterometrinae or Pandininae between the Middle East and the Indian subcontinent.
The ‘Out of India’ hypothesis is often invoked to explain patterns of distribution among Southeast Asian taxa. According to this hypothesis, Southeast Asian taxa originated in Gondwana, diverged from their Gondwanan relatives when the Indian subcontinent rifted from Gondwana in the Late Jurassic, and colonized Southeast Asia when it collided with Eurasia in the early Cenozoic. A growing body of evidence suggests these events were far more complex than previously understood, however. The first quantitative reconstruction of the biogeography of Asian forest scorpions (Scorpionidae Latreille, 1802: Heterometrinae Simon, 1879) is presented here. Divergence time estimation, ancestral range estimation, and diversification analyses are used to determine the origins, dispersal and diversification patterns of these scorpions, providing a timeline for their biogeographical history that can be summarized into four major events. (1) Heterometrinae diverged from other Scorpionidae on the African continent after the Indian subcontinent became separated in the Cretaceous. (2) Environmental stresses during the Cretaceous–Tertiary (KT) mass extinction caused range contraction, restricting one clade of Heterometrinae to refugia in southern India (the Western Ghats) and Sri Lanka (the Central Highlands). (3) Heterometrinae dispersed to Southeast Asia three times during India’s collision with Eurasia, the first dispersal event occurring as the Indian subcontinent brushed up against the western side of Sumatra, and the other two events occurring as India moved closer to Eurasia. (4) Indian Heterometrinae, confined to southern India and Sri Lanka during the KT mass extinction, recolonized the Deccan Plateau and northern India, diversifying into new, more arid habitats after environmental conditions stabilized. These hypotheses, which are congruent with the geological literature and biogeographical analyses of other taxa from South and Southeast Asia, contribute to an improved understanding of the dispersal and diversification patterns of taxa in this biodiverse and geologically complex region.
Loria SF, Prendini L. Out of India, thrice: diversification of Asian forest scorpions reveals three colonizations of Southeast Asia. Sci Rep. 2020;10(1):22301.[Open Access]