Patterns of Post-Glacial Genetic Differentiation in Marginal Populations of a Marine Microalga

Abstract

This study investigates the genetic structure of an eukaryotic microorganism, the toxic dinoflagellate Alexandrium ostenfeldii, from the Baltic Sea, a geologically young and ecologically marginal brackish water estuary which is predicted to support evolution of distinct, genetically impoverished lineages of marine macroorganisms. Analyses of the internal transcribed spacer (ITS) sequences and Amplified Fragment Length Polymorphism (AFLP) of 84 A. ostenfeldii isolates from five different Baltic locations and multiple external sites revealed that Baltic A. ostenfeldii is phylogenetically differentiated from other lineages of the species and micro-geographically fragmented within the Baltic Sea. Significant genetic differentiation (F ST) between northern and southern locations was correlated to geographical distance. However, instead of discrete genetic units or continuous genetic differentiation, the analysis of population structure suggests a complex and partially hierarchic pattern of genetic differentiation. The observed pattern suggests that initial colonization was followed by local differentiation and varying degrees of dispersal, most likely depending on local habitat conditions and prevailing current systems separating the Baltic Sea populations. Local subpopulations generally exhibited low levels of overall gene diversity. Association analysis suggests predominately asexual reproduction most likely accompanied by frequency shifts of clonal lineages during planktonic growth. Our results indicate that the general pattern of genetic differentiation and reduced genetic diversity of Baltic populations found in large organisms also applies to microscopic eukaryotic organisms.

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.…”

Intraspecific facilitation by allelochemical mediated grazing protection within a toxigenic dinoflagellate population

“…The observed high genotypic diversity of phytoplankton populations [9][10][11][12][13] may be sustained by mutualistic interactions of cooperative traits. Yet, with respect to the functioning of extracellular allelochemical substances, the seemingly homogeneous or ephemeral spatial distribution pattern of marine phytoplankton populations and their typical low population densities may contradict with (or limit) the effectiveness of beneficial interactions derived from laboratory experiments with high cell concentration [64].…”

Phylogenetic relationships, morphological variation, and toxin patterns in theAlexandrium ostenfeldii(Dinophyceae) complex: implications for species boundaries and identities

“…Consistent with this view, depending on which RNA region is analyzed and the phylogenetic analysis method employed, the actual order in which various groups appear varies. LSU alignments typically cluster groups 1 and 2 together, whereas ITS alignments sometimes return trees where group 2 strains cluster together with groups 4, 5, and 6 (Gu 2011, Tahvanainen et al 2012). In the concatenated phylogeny presented here, group 1 appears clearly differentiated, whereas the branching of group 2 is poorly resolved, which emphasizes its low divergence from the respective other groups and puts it into an intermediate position between group 1 and groups 4/5/6.…”

“…These isolates span different geographic regions ranging from the subarctic coast of Iceland to tropical South America where the two morphospecies have been recorded in the recent past. New monoclonal strains from the Baltic, Oslofjord/Norway, Iceland, and Canada were grown from cysts isolated from sediment samples as described in Tahvanainen et al (2012). All cultures were maintained at 16°C, 50 lmol photons Á m À2 Á s À1 in f/2 without silica addition (Guillard and Ryther 1962) sterilized filtered local (Baltic) seawater with salinities adjusted to natural conditions of the original environment.…”