Phylogenetic Analyses and Floral Biology of Tacca (Taccaceae) on Borneo

Chua, Kek Shen (2019) Phylogenetic Analyses and Floral Biology of Tacca (Taccaceae) on Borneo. Masters thesis, Universiti Malaysia Sarawak (UNIMAS).

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Abstract

Genus Tacca (Taccaceae) comprises about 20 species with pantropical distribution but mostly occurring in the Old World tropics. Most Tacca species were characterized by its inflorescence with conspicuous bracts and filiform bracteoles. There were two main objectives in this study, which were to resolve the phylogenetic relationship of genus Tacca; and to investigate floral biology of Tacca spp. in Sarawak based on observations, field manipulation, and controlled pollination tests. Phylogenetic relationship between Tacca spp. was analysed using maximum parsimony (MP), maximum likelihood (ML) and Bayesian inference (BI) based on DNA sequences of nuclear internal transcribed spacer (ITS) and plastid maturase K (matK) region. The phylogenetic trees resulted from combined regions showed a congruent topology with work. Tacca bibracteata was closely related to T. palmata, T. palmatifida and T. plantaginea. Tacca borneensis formed sister clade to T. cristata, T. laevis, T. reducta and T. sumatrana. The position of T. reducta in the phylogenetic analysis questioned the previous inflorescence traits evolutionary hypothesis which stated Tacca evolved from reduced to conspicuous floral features. Mapping of morphological characters on the phylogenetic tree indicated that ancestral states of Tacca were palmate leaf blades, long peduncle, large outer involucral bracts, small but greater amount of inner involucral bracts, long bracteoles and higher amount of flowers with less number of ovules. For floral biology, observations were made on T. borneensis, T. cristata, T. laevis, T. leontopetaloides, T. palmata and T. reducta. Flowering period of each species varied with T. leontopetaloides bloomed annually; T. borneensis and T. palmata bloomed sporadically; and T. cristata, T. laevis and T. reducta bloomed continuously. Anthetic period began at 05:30 to 07:00 (UTC + 0800), except T. leontopetaloides which bloomed at 17:00. Their anthetic period lasted for 8 – 14 hours depending on species. The flowers are protogynous. Only flowers of T. laevis and T. leontopetaloides emitted faint floral scent. Pollen: ovule (P:O) ratios fall within the range of facultative self-pollinated species. In Borneo, inflorescence of Tacca spp. received a variety of random insect visitations with female ceratopogonid midge (Culicoides hinnoi & Forcipomyia sp.), stingless bee (Trigona sp.), ant (Formicidae), and mosquito (Culicidae) frequently observed. Among these insects, midge was possibly the main pollinator owing to its accessibility onto the anther and stigma, and its visitation during anthesis. Yet, the efficiency of midge in aiding to outcross Tacca’s flower was not clear owing to its inconsistent visitations and movement within the flower not observed. Moreover, the pollination syndrome developed by Tacca’s inflorescence in attracting pollinator remained unknown, so did the main purpose of developing bracts and bracteoles. Only T. borneensis did not produce any fruit when the floral structures removed. Pollination experiment indicated Tacca spp. in Borneo are self-compatible but not autonomous self-pollinated. Tacca borneensis showed immature fruits abortion in selfing test, indicating inbreeding depression.

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