Abstract
BackgroundThe Philippine archipelago is globally one of the most important model island systems for studying evolutionary processes. However, most plant species on this archipelago have not yet been studied in sufficient detail. The main aim of this study is to unravel the evolutionary history and biogeographic relationships of the Philippine members of the pantropical genus Ixora.ResultsThe complex plastid and nuclear divergence patterns in Philippine Ixora, documented using tree and network approaches, reveal a highly dynamic evolution in Ixora, involving several phases of radiation and recolonization. Philippine Ixora comprises at least five lineages, of which one is most closely related to species from Wallacea, and the remaining four to species from Asia.ConclusionsOur study highlights the importance of Philippine species for understanding phytogeographic patterns in the Indomalayan-Australasian eco-region. The overall genetic differentiation, as well as the incongruence between genealogies based on the biparentally inherited nucleome and the maternally inherited plastome in Ixora, reflect the complex tectonic history of the Philippine archipelago. The Ixora lineage related to Wallacean species supports the delimitation of different ecozones along Huxley’s line, because it is absent from Palawan. The remaining four lineages are all allied with Asian taxa, reflecting several waves of colonization. Close relationships between some widespread Philippine species and locally adapted narrow endemics suggest that the widespread, genetically diverse species act as pools for the formation of new species in a process of ongoing speciation. Our results suggest that the species concepts of some of the more widespread taxa need to be revised.
Highlights
The Philippine archipelago is globally one of the most important model island systems for studying evolutionary processes
The other two nuclear spacers, the ITS2 and the external transcribed spacer (ETS), include sequence portions that will lead to ambiguous alignments when incorporating all Ixoroideae data
We could infer four guide trees based on the harvested data (ETS, Internal transcribed spacer (ITS) excluding non-alignable regions, rps16 intron, entire trnT-F region), which confirmed that our outgroup selection includes the closest relatives of Ixora with best-possible data coverage on the gene regions used here
Summary
The Philippine archipelago is globally one of the most important model island systems for studying evolutionary processes. Most plant species on this archipelago have not yet been studied in sufficient detail. The main aim of this study is to unravel the evolutionary history and biogeographic relationships of the Philippine members of the pantropical genus Ixora. The importance of the Philippine archipelago for Southeast Asian biogeography was first recognized by Alfred Russel Wallace when he distinguished the Australian and Indian regions [1, 2]. He placed the Philippines in the Indian region, but considered them “in some respects of doubtful location”. Biogeographical studies including Philippine plants were conducted only for a few genera such as Cyrtandra J.R.Forst. The endemic Philippine genus Villaria Rolfe (Ixoroideae: Octotropideae) forms a well-supported clade with the Southeast Asian genus Hypobathrum Blume and the West African genus Pouchetia A.Rich. [19]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
