Cryptic diversity and biogeography of the widespread brown alga Colpomenia sinuosa (Ectocarpales, Phaeophyceae)

Recent DNA sequencing studies have demonstrated that many widespread species consist of species complexes with high genetic diversity. The brown alga Colpomenia sinuosa is a suitable candidate for studies into cryptic diversity because of its cosmopolitan distribution in the world's oceans. To examine the genetic diversity within the species and the relationships of the genetic lineages to current distribution, we analyzed a total of 134 cox3 sequences from C. sinuosa specimens collected in 19 countries; we also examined 16 rbcL from a subset of the specimens for comparative purposes. Phylogenetic trees and haplotype analyses of cox3 and rbcL revealed high cryptic diversity comprising three genealogical groups within C. sinuosa. Two groups overlapped in the Indo-Pacific and Atlantic regions, one was confined to the tropics, while the remaining group was localized in the Red Sea and western Mediterranean Sea. Thus, the current distribution of C. sinuosa may well result from a mixture of modern anthropogenic introductions and ancient relicts.