Phylogenetic affinities and distribution of the Hawaiian freshwater red algae (Rhodophyta)

The present study documents the nonmarine red algal species present in the Hawaiian Islands, including their distribution patterns and phylogenetic affinities of the most common taxa. Large-scale survey collections of freshwater algae were made throughout the six largest main Hawaiian Islands, resulting in 155 red algal isolates. Of these, 69 were used for molecular analyses, with DNA sequences generated for four markers from three genomes. Phylogenetic affinities with global reference sequences for the two most common taxa, Composopogon caeruleus (Compsopogonales, Rhodophyta) and the form genus Chantransia, were inferred in an effort to determine the origin of Hawaiian populations. Morphometric measurements and cluster analysis were used to assess the congruence between morphology and molecular data among Chantransia lineages. Phylogeographic patterns within Hawaii were examined for the most common form of Chantransia, Batrachospermum arcuatum (Batrachospermales, Rhodophyta). Seven species of freshwater red algae were found, with some new records for Hawaii. These species had contrasting distributions; some were widespread species, and others were confined to a single island. Molecular data also revealed contrasting patterns for the two most common taxa: one was widespread with no genetic variation even in the context of global sequences, and the other exhibited substantial phylogeographic structure, following the progression rule within the Hawaiian Islands. Morphometric analysis demonstrated little agreement between morphology and molecular data among Chantransia. This is the first comprehensive survey of the freshwater red algae in Hawaii and revealed 28% endemic taxa, with one putative new species reported from Kauai. Contrasting examples of global phylogeographic structure were found; the taxon from which patterns could be deduced showed a western Pacific origin. This study highlights the need for global sampling of freshwater red algae to infer dispersal patterns, especially for those algae with cosmopolitan distributions.