Diversification and biogeography of Dawkinsia (Teleostei: Cyprinidae) in the Western Ghats-Sri Lanka biodiversity hotspot

Abstract

The cyprinid genus Dawkinsia comprises 13 species distributed in lowland streams and rivers in southern peninsular India and Sri Lanka. Eleven species are endemic to India, largely restricted to streams draining the Western Ghats, while one is confined to the Knuckles Hills of Sri Lanka. One species, D. filamentosa, has a wide range, straddling the island and mainland. Here, based on 135 samples representative of all 13 species, collected from 45 locations in India and 17 in Sri Lanka, we present phylogenetic and phylogeographic analyses of Dawkinsia. We use two mitochondrial markers—cytochrome b and cytochrome c oxidase subunit 1. Dawkinsia is recovered as paraphyletic with respect to Sahyadria, with strong node support. The ‘filamentosa group’ which includes both Sri Lankan and Indian taxa (D. filamentosa, D. crassa, D. rohani, D. exclamatio, D. srilankensis, D. tambraparniei, D. arulius, D. rubrotincta and D. uttara) is recovered as the sister group of Sahyadria, a genus confined to the Western Ghats. The ‘assimilis group’, which consists entirely of Indian endemics (D. assimilis, D. austellus, D. apsara and D. lepida), is recovered as the sister group of the ‘filamentosa group’ + Sahyadria. Ancestral-range estimates indicate two colonization events from India to Sri Lanka, across the Palk Isthmus. The first of these, in the Pliocene, involved the common ancestor of D. tambraparniei and D. srilankensis, while the second was of D. filamentosa in the late Pleistocene. Dawkinsia filamentosa shows little phylogeographic structure within or between Sri Lanka and India. Ancestral-range analyses suggest that neither the Palghat nor Shencottah Gaps acted as barriers to the north–south dispersal of Dawkinsia along the Western Ghats. Instead, these valleys appear to have offered lowland passages for west–east colonization by some ancestral species across the Western Ghats ridge. Despite the Palk Isthmus having been subaerial for much of the Plio-Pleistocene and serving as the only terrestrial biotic corridor connecting Sri Lanka to the Asian mainland, it appears to have served also as a climatic filter to dispersal following the aridification of south-eastern India during the Late Miocene/early Pliocene.