Global Diversity and Geographic Distributions of Padina Species (Dictyotales, Phaeophyceae): New Insights Based on Molecular and Morphological Analyses.

The taxonomic status and species diversity of the brown algal genus Padina (Dictyotales, Phaeophyceae) was assessed based on DNA sequences and the morpho-anatomy of specimens collected worldwide, especially from tropical and subtropical western Pacific regions. Phylogenetic analyses using chloroplast rbcL and mitochondrial cox3 gene sequences demonstrated four distinct clades for newly collected samples with high bootstrap support. Each species clade possesses a suite of morphological features that are not shared by any known species of Padina. These are P. imbricata sp. nov., Padina lutea sp. nov., P. moffittianoides sp. nov., and P. nitida sp. nov. The occurrence of these and other species of Padina clearly points to an elevated diversity of the genus in tropical/subtropical waters of the western Pacific. Phylogenetic analyses provided new insights into biogeographic characteristics of the genus, with many species in the Pacific Ocean showing shared/overlapping distributions, whereas species from the Mediterranean/Atlantic and/or the Indian Ocean tend to be confined to particular regions. Consideration has also been given to the evolutionary time frame of the genus Padina based on molecular time trees: a time tree of the concatenated data set (rbcL + cox3) revealed the estimated divergence time in the mid-Cretaceous, whereas those of cox3 and rbcL showed older estimates pointing to the periods of mid-Jurassic and Early Cretaceous, respectively.

Phylogeography and genetic connectivity of the marine macro-alga Sargassum ilicifolium (Phaeophyceae, Ochrophyta) in the northwestern Pacific1.

The evolutionary influences of historical and contemporary factors on the population connectivity and phylogeographic structure of a brown seaweed, Sargassum ilicifolium, were elucidated using the nuclear ITS2 and mitochondrial COI markers for the collections newly sampled within its distribution range in the northwestern Pacific (NWP). Significant genetic structure at variable levels was identified between populations (pairwise FST ) and among populations grouped by geographical proximity (ΦCT among regions). The adjacent groups of populations with moderate structure revealed from AMOVA appeared to have high genetic connectivity. However, a lack of genealogical concordance with the geographic distribution was uncovered for S. ilicifolium from the NWP. Such genetic homogeneity is interpreted as a result of the interaction between postglacial recolonization and dynamic oceanic current regimes in the region. Two separated glacial refugia, the South China Sea and the Okinawa Trough, in the marginal seas of east China were recognized based on the presence of endemic haplotypes and high haplotype diversity in the populations at southern China and northeast of Taiwan. Populations persisting in these refugia may have served as the source for recolonization in the NWP with the rise of sea level during the warmer interglacial periods. The role of oceanic currents in maintaining genetic connectivity of S. ilicifolium in the region was further corroborated by the coherence between the direction of oceanic currents and that of gene flow, especially along the eastern coast of Taiwan. This study underlines the interaction between historical postglacial recolonization and contemporary coastal hydrodynamics in contributing to population connectivity and distribution for this tropical seaweed in the NWP.

Viral RNA Genomes Identified from Marine Macroalgae and a Diatom.

Protists provide insights into the diversity and function of RNA viruses in marine systems. Among them, marine macroalgae are good targets for RNA virome analyses because they have a sufficient biomass in nature. However, RNA viruses in macroalgae have not yet been examined in detail, and only partial genome sequences have been reported for the majority of RNA viruses. Therefore, to obtain further insights into the distribution and diversity of RNA viruses associated with marine protists, we herein examined RNA viruses in macroalgae and a diatom. We report the putative complete genome sequences of six novel RNA viruses from two marine macroalgae and one diatom holobiont. Four viruses were not classified into established viral genera or families. Furthermore, a virus classified into Totiviridae showed a genome structure that has not yet been reported in this family. These results suggest that a number of distinct RNA viruses are widespread in a broad range of protists.

Seasonal population dynamics of Sargassum fusiforme (Fucales, Phaeophyta), Suo-Oshima Is., Seto Inland Sea, Japan-development processes of a stand characterized by high density and productivity.

Seasonal population dynamics of Sargassum fusiforme, one of the most important edible macroalgae in Japan, were studied. Recruits were mainly generated by vegetative reproduction at the margins of filamentous holdfasts. They first appeared in late spring and peaked in summer as upright thalli of the previous generation withered. After producing recruits, holdfasts withered indicating that holdfasts were also annual, the same as upright thalli. All recruits produced main branches and became new upright thalli in early autumn. During this transitional period, the thallus density decreased due to the crowded conditions induced by simultaneous growth initiation. After this early mortality, however, thallus density remained almost constant over much of the growth season. Thallus growth continued during winter and the stand biomass peaked in spring. During this biomass accumulation, development of a thallus size hierarchy was moderate and no size-dependent mortality was observed. Main branch number per thallus was also constant until spring, indicating the main branches also persisted after being produced in early autumn. This lack of severe intraspecific competition both at a thallus and main branch level is supported by the ambient wave condition of the habitat which gives moderate undulation and enables light and nutrients to be supplied to each thallus, and allowed the S. fusiforme stand to maintain its densely-packed feature with a high productivity.