Phylogeography of the marine macroalga Sargassum hemiphyllum (Phaeophyceae, Heterokontophyta) in northwestern Pacific

Abstract

Sargassum hemiphyllum is commonly found in Japan and Korea, with a variety, var. chinense, that is found distributed in the southern Chinese coast. We previously reported distinct genetic differentiation between the two taxa based on the PCR-RFLP data of plastid RubiscoL-S spacer. The present study aims at elucidating the phylogeographic pattern of S. hemiphyllum based on more markers in the nuclear and extranuclear genomes, with a view to reveal the occurrence of hybridization. The two allopatrically distributed taxa were found to be genetically distinct in nuclear ITS2, plastidial Rubisco (Rbc) and mitochondrial TrnW_I (Trn) spacers. Their divergence was postulated to be attributable to the vicariant event which resulted from the isolation of the Sea of Japan during the late Miocene (6.58-11.25 Mya). Divergence within both S. hemiphyllum and the chinense variety was observed based on Trn spacer, while the divergence in S. hemiphyllum was further confirmed in Rbc spacer. This divergence appears to correspond to the separation of the Japanese populations between the Sea of Japan and the Pacific that occurred around 0.92-2.88 Mya (the early Pleistocene). The presence of an ITS2 clone resembling var. chinense sequences in a Japanese population of S. hemiphyllum (JpNS) raises the possibility of the introgression of var. chinense individuals into S. hemiphyllum population. Compared to that between S. hemiphyllum and the chinense variety, hybridization among the Japanese and Korean populations of S. hemiphyllum is highly probable as all these individuals share a pool of nuclear ITS2 sequences, possibly attributable to incomplete concerted evolution of ITS2.

The impact of Yangtze River discharge on the genetic structure of a population of the rock bream,Oplegnathus fasciatus

“…The disruption of the southward East China Sea Coastal Current due to the impact of the summer monsoon and discharge from the Yangtze River during the reproductive season of O. fasciatus may cause a disconnection between the Yellow Sea populations and the East China Sea populations (Dong et al 2012). Similar results of gene-flow disruption among populations by the Yangtze River were also reported in Chelon haematocheilus (Temminck & Schlegel, 1845), Sargassum hemiphyllum (Agardh), Cyclina sinensis (Gmelin, 1791) and Cellana toreuma (Reeve, 1854) along the continental slope of the Asian Pacific (Liu et al 2007;Zhao et al 2009;Cheang et al 2010;Dong et al 2012). Frequent gene flow was detected between the ZS and TW locations in the present study.…”

“…It has been reported that the Yangtze Delta was formed at least 3.2 million years ago based on the provenance of the sediment in the area of the modern delta (Jia et al 2010). AMOVA, F st and Φ pt analyses revealed limited gene exchange between the JN and ZS locations separated by the Yangtze River estuary, suggesting that the Yangtze River acted as a barrier to gene flow among populations on either side, which has also been observed in other marine species (Liu et al 2007;Zhao et al 2009;Cheang et al 2010;Dong et al 2012). According to the divergence time of the two stocks of O. fasciatus, we could conclude that it was at least 0.31-0.41 million years since the Yangtze River began to significantly influence the gene exchange among populations of O. fasciatus.…”

Phylogeography of Diptychus maculatus (Cyprinidae) endemic to the northern margin of the QTP and Tien Shan region

“…Complete sequence of Cyt b gene, partial sequences of the 16S rRNA, D-loop and RAG-2 genes were obtained for all the sampled individuals. When direct sequencing of RAG-2 failed due to heterozygosity, amplicons of RAG-2 were cloned using a TA-cloning system (TakaRa Biotechnology, Dalian, China) following the manufacturer’s instructions [38]. The master mixture of polymerase chain reaction (PCR) contained approximately 100 ng of template DNA, 1 μL (10 pmol) of each primer, 5 μL of 10× reaction buffer, 2 μL of dNTPs (2.5 mM of each) and 2.0 U of Taq DNA polymerase, in a total volume of 50 μL.…”

Causations of phylogeographic barrier of some rocky shore species along the Chinese coastline

“…This together with the Yangtze River discharge is assumed to form a contemporary dispersal barrier for marine species that require a hard substratum (e.g. intertidal rocky shore) or with larvae that cannot tolerant decreased salinity, including the gastropod Cellana toreuma [20], the bivalve Cyclina sinensis [34] and the macroalga Sargassum hemiphyllum [18, 35]. However, studies on other coastal fauna did not detect any genetic split across the Yangtze River [24].…”