Systematics, distribution, and sexual compatibility of six Scytosiphon species (Scytosiphonaceae, Phaeophyceae) from Japan and the description of four new species.

The brown alga Scytosiphon lomentaria (Scytosiphonaceae, Ectocarpales) has been reported from cold and warm waters worldwide. Although previous molecular phylogenetic studies and crossing experiments have shown that it is a complex of multiple distinct species, the taxonomic position and accurate distribution of each species have remained largely unclear. For the S. lomentaria complex from Japan, our cox1 and rbcL phylogenetic analyses detected six species. In addition to five previously detected species (species Ia-Va), one species (species VI) was newly found in the subtropical area, Okinawa Island. Species VI was recovered as a sister to species Ia-Va in rbcL. Based on the morphological and phylogenetic data, we concluded that species Ia is S. lomentaria, species IIIa is S. promiscuus, and the other four species are newly described: S. shibazakiorum for species IIa, S. tosaensis for species IVa, S. arcanus for species Va, and S. subtropicus for species VI. The cox1-based analysis also showed that S. lomentaria, S. shibazakiorum, and S. promiscuus have worldwide distributions, while the other three species were not found outside of Japan. In Japan, except for S. subtropicus, distributions of these species overlapped. Our crossing experiments showed that gametic incompatibility (pre-zygotic barrier) was less developed between the allopatric species (i.e., S. subtropicus and others) compared with the sympatric species. It may suggest that pre-zygotic barriers have evolved among the sympatric species due to reinforcement.

A molecular investigation of the genus Ecklonia (Phaeophyceae, Laminariales) with special focus on the Southern Hemisphere.

Brown algae of the order Laminariales, commonly referred to as kelps, are the largest and most productive primary producers in the coastal inshore environment. The genus Ecklonia (Lessoniaceae, Phaeophyceae) consists of seven species with four species in the Northern Hemisphere and three in the Southern Hemisphere. It was recently transferred to the family Lessoniaceae based on phylogenetic analyses of nuclear and chloroplastic markers, though the type of the genus was not included and its relationship with allied genera Eckloniopsis and Eisenia remained unresolved. The present study is the first to produce a phylogeny focussed on the genus Ecklonia. It included sequences from nuclear, mitochondrial, and chloroplastic DNA, for most of the distribution range of the three current Southern Hemisphere species (Ecklonia radiata, Ecklonia maxima, and a sample of a putative Ecklonia brevipes specimen), sequences for East Asiatic species (Ecklonia cava, Ecklonia kurome, and Ecklonia stolonifera), as well as the closely related genera Eckloniopsis and Eisenia. Results confirmed E. radiata and E. maxima as two distinct species in South Africa, E. radiata as a single species throughout the Southern Hemisphere (in South Africa, Australia, and New Zealand) and East Asiatic species as a distinct lineage from the Southern Hemisphere clade. Results further pointed out a close sister relationship between Eckloniopsis radicosa and two Eisenia species (including the type species: Eisenia arborea) to the genus Ecklonia suggesting that the genera Eckloniopsis and Eisenia are superfluous.

Phylogeographic heterogeneity of the brown macroalga Sargassum horneri (Fucaceae) in the northwestern Pacific in relation to late Pleistocene glaciation and tectonic configurations.

Pleistocene glacial oscillations and associated tectonic processes are believed to have influenced the historical abundances and distribution of organisms in the Asia Northwest Pacific (ANP). Accumulating evidence indicates that factors shaping tempospatial population dynamics and distribution patterns of marine taxa vary with biogeographical latitude, pelagic behaviour and oceanographic regimes. To detect what kinds of historical and contemporary factors affected genetic connectivity, phylogeographic profiles of littoral macroalga Sargassum horneri in the ANP were analysed based on mitochondrial (Cox3) and chloroplast (rbcL) data sets. Five distinct clades were recovered. A strong signature of biogeographical structure was revealed (Φ(CT) = 0.487, P < 0.0001) derived from remarkable differentiation in clade distribution, as clade I is restricted to Chinese marginal seas (Yellow-Bohai Sea, East China Sea and South China Sea), whereas clades II-V are discontinuously scattered around the main Islands of Japan. Furthermore, two secondary contact regions were identified along the south Japan-Pacific coastline. This significant differentiation between the two basins may reflect historical glacial isolation in the northwestern Pacific, which is congruent with the estimates of clade divergence and demographic expansion during the late Quaternary low sea levels. Analysis of molecular variance and the population-pair statistic F(ST) also revealed significant genetic structural differences between Chinese marginal seas and the Japanese basin. This exceptional phylogeographic architecture in S. horneri, initially shaped by historical geographic isolation during the late Pleistocene ice age and physical biogeographical barriers, can be complicated by oceanographic regimes (ocean surface currents) and relocating behaviour such as oceanic drifting.