Genetic structuring and transfer of marine dinoflagellate Cochlodinium polykrikoides in Japanese and Korean coastal waters revealed by microsatellites

Abstract

To determine the process of population expansion and ascertain the origin of the Sea of Japan population, in a noxious red tide forming dinoflagellate Cochlodinium polykrikoides, 13 samples, isolated from 11 different localities in Japanese and Korean coasts, were analysed using 10 polymorphic microsatellites. Analyses by nonmetric multidimensional scaling plots of pairwise F(ST), global amova, and genetic admixture analysis identified three clusters--the Sea of Japan populations, Yatsushiro Sea (Kumamoto Pref.) populations, and other populations--indicating genetic structuring of the 13 samples into three distinct populations. In the proportion of shared alleles by pairwise individuals (P(SAxy)) analyses between the Sea of Japan and the other samples, P(SAxy) was extremely low compared with that among the Sea of Japan or among other samples, indicating that a large genetic barrier has occurred between the populations. No significant relationship of isolation-by-distance patterns and almost no genetic distance were detected between pairwise samples of the Sea of Japan, although there is a maximal distance of > 600 km between samples. In addition, P(SAxy) data among the samples were extremely high compared with those among other samples, clearly showing that a large-scale transfer from west to east has occurred via the Tushima Warm Current. In the P(SAxy) data of the Seto Inland Sea and Pacific samples, individuals showing relatively high P(SAxy) were concentrated in the three areas of Nagasaki, Harima, and Mie, suggesting that frequent transfer may have occurred by human-assisted dispersal, although Nagasaki and Mie are separated by a distance of approximately 700 km.

Hundred years of genetic structure in a sediment revived diatom population

“…Genetic differentiations of similar magnitudes between populations of seemingly well-connected habitats have been confirmed previously for S. marinoi (22), for a different diatom (26), and for a few other marine protists (10,27). However, the most remarkable outcome is that diatom populations can be extremely long lived, and patterns of genetic structure are well conserved.…”

“…Because of predominant asexual division, it also has been assumed that populations consist of only a few clones. This assumption has been challenged recently by an increasing number of studies demonstrating high genetic and phenotypic diversity in populations of eukaryotic microorganisms (8)(9)(10).…”

Limits to gene flow in a cosmopolitan marine planktonic diatom

“…Flow patterns of tidal or oceanic currents may also contribute to the genetic isolation among global populations by hindering dispersal (22,23,28,58,59). For example, there were no significant F ST values between populations from the North Sea and a connected Danish inland fjord, yet populations from the Irish Sea and the adjacent North Sea showed significant differentiation.…”

“…To date, population genetic studies of high-dispersal organisms in the marine environment have largely focused on pelagic or benthic animals with planktonic larval stages (21)(22)(23)(24). Population genetic structuring of planktonic microorganisms has been much less explored due to difficulties with species delineation and lack of finescale genetic markers for these organisms (25)(26)(27)(28).…”

An attempt to semi-quantify potentially toxic diatoms of the genus <i>Pseudo-nitzschia</i> in Tokyo Bay, Japan by using massively parallel sequencing technology

“…Thus, monitoring programs that focus only on the detection of DA concentrations higher than the regulatory limit in shellfish do not guarantee the safety of food or the protection of human health. Furthermore, there is compelling evidence that the geographic ranges of both the toxic dinoflagellate Alexandrium tamarense species complex and the bivalve killer dinoflagellate Heterocapsa circularisquama Horiguchi have been expanded by human-assisted means, such as translocation of oyster spats and/or cargo vessel ballast water (Anderson 1989, Hallegraeff & Bolch 1992, Honjo et al 1998, Nagai et al 2009, Matsuyama et al 2010. These findings suggest that, in the future, populations of highly toxic Pseudo-nitzschia may be introduced from elsewhere and may coexist with existing populations in Japanese coastal waters.…”