Phylogenetics and Evolution of the Paleotropical Woody Bamboos (Poaceae: Bambusoideae: Bambuseae)

Abstract

<p>The paleotropical woody bamboos (PWB) are members of Bambuseae (tropical woody bamboos) in subfamily Bambusoideae of the grass family (Poaceae). Although the PWB are important in ecological and economic functions, the phylogenetic relationships of the PWB remain equivocal. All four currently recognized subtribes of the PWB have never been completely examined for their evolutionary relationships and no morphological synapomorphy of the PWB has ever been revealed in previously published work. Six chloroplast sequences with coding (ndhF3' and matK) and non-coding (rpl16 intron, rps16 intron, trnD-trnT spacer, and trnT-trnL spacer) regions and three low-copy nuclear sequences (GPA1, Pabp1, and PvCel1) are analyzed to clarify the systematics and evolution of the PWB based on maximum parsimony, maximum likelihood and Bayesian inference. Forty morphological and anatomical characters are analyzed and mapped on the respective plastid and nuclear consensus trees. The objectives of this study are to: (1) test the monophyly of the PWB and all subtribes using chloroplast and low-copy nuclear sequences; (2) examine the phylogenetic relationships of all subtribes in the PWB clade based on molecular analyses; and (3) evaluate morphological evolution of the PWB.</p> <p>The PWB form a monophyletic group with six clades [Bambusinae, Madagascan Hickeliinae, Melocanninae, Racemobambosinae, CDMNPS (Cyrtochloa-Dinochloa-Mullerochloa-Neololeba-Parabambusa-Pinga-Sphaerobambos) + Greslania, and Temburongia] and are sister to the Neotropical woody bamboo (NWB) clade based on plastid and nuclear markers. The relationships among subtribes of the PWB are different between two molecular topologies. The plastid analysis supports the monophyly of Melocanninae and its position as sister to the remaining PWB. Within PWB and exclusive of Melocanninae, Madagascan Hickeliinae form a monophyletic group sister to the rest of the PWB. Non-Madagascan Nastus are clustered with Racemobambosinae to form a clade. The core Bambusinae basically consists of a polytomy and the CDMNPS + Greslania clade is removed from subtribe Bambusinae and resolved as sister to the Racemobambosinae. In the nuclear analysis, the six lineages of the PWB from a polytomy, and six diverse genomic components are representative of Bambusoideae: one genome for the herbaceous bamboos (H), two genomes each for the temperate woody bamboos (genomes A and B) and the NWB (genomes C and D), and three genomes for the PWB (genomes C, D, and E). However, some taxa of the PWB show variation of genomic components from one to three genomes.</p> <p>The incongruence between plastid and nuclear analyses is most strongly indicated at the tribal rank. The chloroplast analysis strongly supports the tropical woody bamboos as sister to the herbaceous bamboos, forming a tropical bamboo clade, with this clade sister to the temperate woody bamboos, whereas the low-copy nuclear analysis strongly supports the woody bamboo clade (tropical + temperate woody bamboos) as sister to the herbaceous bamboos.</p> <p>Morphological investigation suggests that the presence of six stamens is a potential synapomorphy of the PWB. Melocanninae exhibit a narrow and glabrous ovary with an elongated and hollow style. The presence of extravaginal or infravaginal branching with a dipping nodal line is a unique character combination of Hickeliinae. Climbing bamboos with a wrinkled and prominent girdle diagnose the CDMNPS clade. Racemobambosinae + non-Madagascan Nastus possess a cap on the top of ovary apex with short style, whereas the Temburongia clade exhibits a blunt ovary apex without cap and moderate style length.</p>