Exploring an enigma: the geographic and temporal origins of the Western Ghats flora

Abstract

The Western Ghats are an ancient mountain range with an origin dating back to the Late Jurassic, with an extraordinarily diverse and endemic flora. The biodiversity of these sky islands has been influenced by the separation of India from Gondwana during the Late Jurassic period, and its ultimate collision with the Eurasian plate in the late Cretaceous. As a consequence, the flora of the Western Ghats has the potential to have accreted from several regions, including Africa, the Himalayas, Continental Asia, and the Sunda Shelf. There is an emerging paradigm of tropical floras being geologically young and being driven by high rates of species turnover. However, the unique journey of the Indian subcontinent alludes to the presence of an entirely unique floristic diversity in the Western Ghats, which has not been empirically studied in depth to date. The aim of this thesis is to understand the temporal and geographic origins of the Western Ghats flora. A herbarium genomics approach was employed (Whole Genome Sequencing) to assemble DNA regions of species native or endemic to the Ghats and incorporate them into existing phylogenetic datasets of plant families with wider tropical distributions. Time-calibrated phylogenies and ancestral range evolution models were used to provide a synthetic view of the flora’s origins using the families Annonaceae, Begoniaceae, Chloranthaceae, Dipterocarpaceae, Ebenaceae, Lauraceae, Sapotaceae, and Zingiberaceae as representatives. The ancestral area reconstructions show that the Western Ghats flora originated predominantly from the regions of Continental Asia and the Sunda Shelf during the Miocene-Pliocene period, showing a flora strongly influenced by geologically recent dispersal rather than ancient vicariance.