Florideophycean red algal phylogeny and divergence time.

Abstract

The Florideophyceae is the most abundant and taxonomically diverse group (more than 6,700 spp) of Rhodophyta, consisting five subclasses, i.e., Ahnfeltiophycidae, Corallinophycidae, Hildenbrandiophycidae, Nemaliophycidae, and Rhodymeniophycidae. However, many aspects of the systematics (i.e., diversity, phylogeny and taxomony) and divergence times of the group remain uncovered. In present study, we used a seven-gene concatenated dataset (nDNA EF2, LSU and SSU rRNAs, mtDNA cox1,&#8232 and ptDNA rbcL, psaA and psbA genes) and generated a robust phylogeny. Our results provide robust estimates for the divergence times of major lineages within the Florideophyceae. New multigene relaxed molecular clock analyses suggest that the Florideophyceae and Bangiophyceae diverged from MRCA approximately 943 ±57 million years ago (Ma with 817&#8211 1,049 Ma 95% confidence intervals, CI). The major divergences in the class involved the emergence of Hildenbrandiophycidae [ca. 781 ±48 (CI: 681&#8211 879) Ma], Nemaliophycidae [ca. 661 ±34 (CI: 597&#8211 736) Ma], Corallinophycidae [ca. 579 ±18 (CI: 543&#8211 617) Ma], and the split of Ahnfeltiophycidae and Rhodymeniophycidae [ca. 508 ±34 (CI: 442&#8211 580) Ma]. Divergences within the Florideophyceae were accompanied by complete triphasic life cycle and subsequeces change in the cell-to-cell fusion mechanisms, leading to a successful strategy for millions of spore production from idae. However, many aspects of the systematics (i.e., diversity, phylogeny and taxomony) and divergence times of the group remain uncovered. In present study, we used a seven-gene concatenated dataset (nDNA EF2, LSU and SSU rRNAs, mtDNA cox1,&#8232 and ptDNA rbcL, psaA and psbA genes) and generated a robust phylogeny. Our results provide robust estimates for the divergence times of major lineages within the Florideophyceae. New multigene relaxed molecular clock analyses suggest that the Florideophyceae and Bangiophyceae diverged from MRCA approximately 943 ±57 million years ago (Ma with 817&#8211 1,049 Ma 95% confidence intervals, CI). The major divergences in the class involved the emergence of Hildenbrandiophycidae [ca. 781 ±48 (CI: 681&#8211 879) Ma], Nemaliophycidae [ca. 661 ±34 (CI: 597&#8211 736) Ma], Corallinophycidae [ca. 579 ±18 (CI: 543&#8211 617) Ma], and the split of Ahnfeltiophycidae and Rhodymeniophycidae [ca. 508 ±34 (CI: 442&#8211 580) Ma]. Divergences within the Florideophyceae were accompanied by complete triphasic life cycle and subsequeces change in the cell-to-cell fusion mechanisms, leading to a successful strategy for millions of spore production from