MICROSATELLITE MARKERS REVEAL POPULATION GENETIC STRUCTURE OF THE TOXIC DINOFLAGELLATE ALEXANDRIUM TAMARENSE (DINOPHYCEAE) IN JAPANESE COASTAL WATERS¹

Abstract

This is the first report to explore the fine-scale diversity, population genetic structure, and biogeography of a typical planktonic microbe in Japanese and Korean coastal waters and also to try to detect the impact of natural and human-assisted dispersals on the genetic structure and gene flow in a toxic dinoflagellate species. Here we present the genetic analysis of Alexandrium tamarense (Lebour) Balech populations from 10 sites along the Japanese and Korean coasts. We used nine microsatellite loci, which varied widely in number of alleles and gene diversity across populations. The analysis revealed that Nei's genetic distance correlated significantly with geographic distance in pair-wise comparisons, and that there was genetic differentiation in about half of 45 pair-wise populations. These results clearly indicate genetic isolation among populations according to geographic distance and restricted gene flow via natural dispersal through tidal currents among the populations. On the other hand, high P-values in Fisher's combined test were detected in five pair-wise populations, suggesting similar genetic structure and a close genetic relationship between the populations. These findings suggest that the genetic structure of Japanese A. tamarense populations has been disturbed, possibly by human-assisted dispersal, which has resulted in gene flow between geographically separated populations. 1

Bioactive compounds of marine dinoflagellate isolates from western Greenland and their phylogenetic association within the genus Alexandrium

“…A more thorough analysis of genetic divergence based upon a number of nuclear markers, such as microsatellites or amplified fragment length polymorphism (AFLP), might reveal a more pronounced genetic divergence within A. tamutum on the population level. Such patterns have already been found for other species of the genus, such as A. tamarense Group I/North American ribotype (Nagai et al, 2007) or Alexandrium ostenfeldii (Tahvanainen et al, 2012), respectively.…”

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.…”

Population genetics: the next stop for microbial ecologists?

“…Even if dispersal is high, the environment may show enough heterogeneity to promote diversification through adaptive selection. Adaptive diversification may also be favored by the large genetic diversity that seems to be present in microbial populations [14][15][16][17][18][19][20]. Natural selection can act over this vast diversity and fine-tune different microbial populations to their respective environments.…”

“…However, the few available studies indicate a number of interesting patterns. For instance, in microeukaryotes, genetically distinct microbial populations can occur in marine environments despite the constant flow of currents [19,[22][23][24]. In addition, different lakes can harbor genetically distinct microbial populations, and in some cases, distinct populations can even coexist within the same water body [20,25].…”