Polar lakes may act as ecological islands to aquatic protists

K Rengefors,R Logares,J Laybourn‐Parry

doi:10.1111/j.1365-294x.2012.05596.x

Abstract

A fundamental question in ecology is whether microorganisms follow the same patterns as multicellular organisms when it comes to population structure and levels of genetic diversity. Enormous population sizes, predominately asexual reproduction and presumably high dispersal because of small body size could have profound implications on their genetic diversity and population structure. Here, we have analysed the population genetic structure in a lake-dwelling microbial eukaryote (dinoflagellate) and tested the hypothesis that there is population genetic differentiation among nearby lake subpopulations. This dinoflagellate occurs in the marine-derived saline lakes of the Vestfold Hills, Antarctica, which are ice-covered most of the year. Clonal strains were isolated from four different lakes and were genotyped using amplified fragment length polymorphism (AFLP). Our results show high genetic differentiation among lake populations despite their close geographic proximity (<9 km). Moreover, genotype diversity was high within populations. Gene flow in this system is clearly limited, either because of physical or biological barriers. Our results discard the null hypothesis that there is free gene flow among protist lake populations. Instead, limnetic protist populations may differentiate genetically, and lakes act as ecological islands even on the microbial scale.

Highlights

Eukaryotic microorganisms are a very large and diverse group of organisms that are comparatively little studied within ecology and evolutionary ecology (e.g. Gerstein & Moore 2011)
Population genetic theory predicts high genetic diversity in microbial populations because of their population size, which has been confirmed by population genetic simulations (Mes 2008)
Using population genetic tools and molecular markers, we investigated whether gene flow is unlimited and whether population genetic structure was present in an aquatic free-living protist species (Dinophyceae) found in Antarctic saline lakes

Summary

Introduction

Eukaryotic microorganisms (protists) are a very large and diverse group of organisms that are comparatively little studied within ecology and evolutionary ecology (e.g. Gerstein & Moore 2011). Protists generally have enormous population sizes, small body size and high reproductive rates (which are partially or entirely asexual). These features probably have profound implications for both intraspecific genetic diversity and population structure (Mes 2008). Bengtsson (2003) showed that predominately asexual species started by sexually produced propagules (e.g. dinoflagellate resting cysts) can maintain initial genotypic variation for an extended time before any effect of clonality can be detected. Simulations suggest that with mainly asexual reproduction, there will be high diversity at single loci, with fewer multilocus genotypes (more clonality) compared to sexually reproducing species (Balloux et al 2003). Protists populations with yearly sexual events should not differ from sexually reproducing species, empirical data are still largely lacking

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