Genetic Diversity and Phylogeography of a Turf-Forming Cosmopolitan Marine Alga, (Gelidiales, Rhodo-Phyta).

Cosmopolitan species are rare in red algae, which have a low-dispersal capacity unless they are dispersed by human-mediated introductions. , a turf-forming red alga, has a widespread distribution in tropical and temperate waters. To decipher the genetic diversity and phylogeography of , we analyzed mitochondrial COI-5P and plastid L sequences from collections in the Atlantic, Indian, and Pacific Oceans. Phylogenies of both markers statistically supported the monophyly of , with a close relationship to and from the Western Atlantic. Based on the molecular analysis from these materials, from India is here merged with . Phylogeny and TCS networks of COI-5P haplotypes revealed a geographic structure of five groups: (i) Atlantic-Mediterranean, (ii) Ionian, (iii) Asian, (iv) Adriatic-Ionian, and (v) Australasia-India-Tanzania-Easter Island. The most common ancestor of likely diverged during the Pleistocene. The Bayesian Skyline Plots suggested the pre-LGM population expansion. Based on geographical structure, lineage-specific private haplotypes, the absence of shared haplotypes between lineages, and AMOVA, we propose that the cosmopolitan distribution of has been shaped by Pleistocene relicts. The survival of the turf species under environmental stresses is briefly discussed.