Format: ORAL

Hong-Wun Chen1, Yu-Hsin Tseng2, Shih-Hui Liu3, Li-Wei Tsai1, Ai-Qun Hu4 and Kuo-Fang Chung1

1 Biodiversity Research Center, Academia Sinica, Taipei, Taiwan 2 Department of Life Sciences, Taichung, Taiwan 3 Department of Biological Sciences, Kaohsiung, Taiwan 4 Singapore Botanic Gardens, 1 Cluny Road, Singapore

With more than 2,000 species exhibiting striking morphological variation, the mega-diverse genus Begonia has emerged as a fascinating system for studying plant speciation. Many explanations, such as genome size variation, polyploidization, hybridization, and geographical isolation, have been proposed as the potential drivers for its high species richness. However, few studies have studied the role of phenotypic variation has played in facilitating ecological adaptation and triggering speciation. One unique morphological anatomic feature in some Begonia species is the presence of stomatal cluster and hypodermis that are beneficial for growing in arid habitats; however, the evolutionary importance of these anatomical traits has never been investigated under a broad phylogenetic context. Based on a highly resolved phylogenomic tree of Asian Begonia reconstructed using target capture data, phylogenetic comparative analyses of three characters (i.e., singular vs. clustered stomata, absence vs. presence of hypodermis, and epiphytic vs. lithophytic vs. terrestrial) were conducted. Our study demonstrates strong and significant phylogenetic signals in all three characters and reveals high concordance between both leaf anatomical traits with habitat preference, implying a high degree of phylogenetic niche conservatism in Begonia. However, the transition from singular to clustered stomata had occurred mainly in the common ancestors of B. sect. Baryandra and B. sect. Jackia distributed mainly in limestone karsts of the Philippines, Malaysia and Indonesia, respectively. Considering the biogeographic origin mainly mediated by long-distance dispersal in B. sect. Baryandra, our findings suggest that, after the common ancestors of B. sect. Baryandra dispersed to the Philippines, the possession of stomatal cluster and hypodermis could have facilitated the successful colonization to the limestone habitats throughout the archipelago. By integrating multiple data sets, our study demonstrates how phenotypic variation and ecological adaptation could have triggered an exceedingly high speciation rate in the megadiverse Begonia.