Pandanus plastomes decoded: When climate mirrors morphology and phylogenetic relationships.

Area of Science:

• Botany
• Evolutionary Biology
• Phylogenetics

Background:

• Pandanus (Pandanaceae) is a diverse genus of paleotropical monocots.
• Previous phylogenetic studies using limited DNA regions were inconclusive regarding the monophyly of Pandanus subgenera.
• Low phylogenetic branch support hindered detailed evolutionary investigations.

Purpose of the Study:

• To test the monophyly of Pandanus subgenera using comprehensive genomic data.
• To identify morphological synapomorphies (shared derived traits) within Pandanus clades.
• To investigate the relationship between leaf anatomy, specifically water storage tissue, and climatic differentiation.
• To reconstruct the spatiotemporal evolutionary history of the Pandanus genus.

Main Methods:

• Genome skimming was employed to sequence 50 Pandanus species, reconstructing their plastomes.
• Phylogenetic trees were inferred using partitioned RAxML and BEAST analyses to test subgeneric monophyly and perform ancestral state reconstructions.
• Shimodaira-Hasegawa tests were utilized for monophyly testing.
• Random forests were used to compare climatic and soil conditions across phylogenetic clades.
• Correlations between current morphology, climate niche, and past climate events were analyzed.

Main Results:

• Phylogenetic analyses identified two major clades and four subclades within Pandanus.
• Only the subgenus Coronata was found to be monophyletic.
• Morphological synapomorphies, particularly in staminate structures, were identified for three subclades.
• Hypertrophied and hyperplasic water-storage tissue was identified as a synapomorphy for clade II, associated with seasonal climates and well-draining soils.
• Clade differentiation occurred during the early Miocene, coinciding with the Southeast Asian monsoon, while subclades diverged during the Miocene Thermal Maximum.

Conclusions:

• The current subgeneric classification of Pandanus requires revision based on phylogenetic findings.
• The evolution of hypertrophied and hyperplasic water-storage tissue is a critical factor in Pandanus adaptation.
• This key trait likely explains observed climatic and biogeographic patterns by enabling photosynthesis under hydric stress.