Hundred years of genetic structure in a sediment revived diatom population

Abstract

This paper presents research on the genetic structure and diversity of populations of a common marine protist and their changes over time. The bloom-forming diatom Skeletonema marinoi was used as a model organism. Strains were revived from anoxic discrete layers of a 210 Pb-dated sediment core accumulated over more than 100 y, corresponding to >40,000 diatom mitotic generations. The sediment core was sampled from the highly eutrophic Mariager Fjord in Denmark. The genetic structure of S. marinoi was examined using microsatellite markers, enabling exploration of changes through time and of the effect of environmental fluctuations. The results showed a stable population structure among and within the examined sediment layers, and a similar genetic structure has been maintained over thousands of generations. However, established populations from inside the fjord were highly differentiated from open-sea populations. Despite constant water exchange and influx of potential colonizers into the fjord, the populations do not mix. One fjord population, accumulated in 1980, was significantly differentiated from the other groups of strains isolated from the fjord. This differentiation could have resulted from the status of Mariager Fjord, which was considered hypereutrophic, around 1980. There was no significant genetic difference between preand posteutrophication groups of strains. Our data show that dispersal potential and generation time do not have a large impact on the genetic structuring of the populations investigated here. Instead, the environmental conditions, such as the extreme eutrophication of the Mariager Fjord, are deemed more important. microevolution | microsatellites

Evidence for environmental and ecological selection in a microbe with no geographic limits to gene flow

“…The detection of significantly diverged populations in samples collected over short periods of time (1-6 wk) contrasts with observations of genetic stability in fjords (54). In contrast to the long hydrographic residence times of fjord systems, Narragansett Bay, site 17, experiences a very short residence time of 10-40 d (56).…”

“…In the Danish Mariager fjord, population stability over 100 y has been observed in the centric diatom species Skeletonema marinoi (54). The Mariager fjord is associated with a remarkably low flushing rate of 8 mo (54).…”

“…If microbes evolve more quickly than global circulation patterns can disperse them, we would expect biogeographic patterns to emerge; the potential for biogeographic patterns deriving from neutral evolution has been demonstrated in recent modeling efforts (18). Because we observed no correlation between geographic distance and population divergence on global scales, but still observed distinct populations in this species, it is likely that divergence observed in T. rotula populations is a product of ongoing selective forces that reduce gene flow among populations and allow them to persist over time frames greater than decadal-scale global surface seawater connectivity and perhaps even longer, given empirical evidence in the diatom S. marinoi, which exhibits stable F ST divergence on time scales of 100 y (54). The presence of distinct populations among global samples of T. rotula demonstrates that selective mechanisms exist to support divergence within the species.…”

A global perspective on marine photosynthetic picoeukaryote community structure

“…However, most of our knowledge about how biodiversity varies across large spatial scales comes from research on macroorganism biogeography, with only relatively few recent studies for microorganisms (for example, see Foissner, 2006;Fuhrman et al, 2008;Caron, 2009;Nolte et al, 2010). Opposing views have claimed that, on one hand, free-living microbial taxa present a cosmopolitan distribution Fenchel, 2004, Finlay et al, 2006;Pither, 2007), with particular implications for organisms in the smallest size classes (for example, o0.5 mm; Yang et al, 2010), and, on the other, are composed primarily of species that have limited geographical distributions (Papke and Ward, 2004;Telford et al, 2006;Härnströ m et al, 2011).…”

A combined paleolimnological/genetic analysis of diatoms reveals divergent evolutionary lineages of Staurosira and Staurosirella (Bacillariophyta) in Siberian lake sediments along a latitudinal transect

“…Such sequencing studies on sediment material employed genetic markers to recover recent-or paleo-biodiversity from taxa that are difficult to identify from their morphologies alone (Anderson-Carpenter et al 2011;Boere et al 2011;Jørgensen et al 2012), either because they leave no fossil remains or because the taxonomic diversity is concealed within similar or identical morphotypes (Stoof-Leichsenring et al 2012). Most genetic studies of environmental samples have aimed at species determination, but a few attempts have been made to recover genetic variations within a species or a species-complex (Epp et al 2010;Härnström et al 2011).…”