title: Genotypic diversity and differentiation among populations of two benthic freshwater diatoms as revealed by microsatellites.
abstract: Given their large population sizes and presumed high dispersal capacity, protists are expected to exhibit homogeneous population structure over large spatial scales. On the other hand, the fragmented and short-lived nature of the lentic freshwater habitats that many protists inhabit promotes strong population differentiation. We used microsatellites in two benthic freshwater diatoms, Eunotia bilunaris 'robust' and Sellaphora capitata, sampled from within a pond and connected ponds, through isolated ponds from the same region to western Europe to determine the spatial scale at which differentiation appears. Because periods of low genotypic diversity contribute to population differentiation, we also assessed genotypic diversity. While genotypic diversity was very high to maximal in most samples of both species, some had a markedly lower diversity, with up to half (Eunotia) and over 90% (Sellaphora) of the strains having the same multilocus genotype. Population differentiation showed an isolation-by-distance pattern with very low standardized FST values between samples from the same or connected ponds but high values between isolated ponds, even when situated in the same region. Partial rbcL sequences in Eunotia were consistent with this pattern as isolated ponds in the same region could differ widely in haplotype composition. Populations identified by Structure corresponded to the source ponds, confirming that 'pond' is the main factor structuring these populations. We conclude that freshwater benthic diatom populations are highly fragmented on a regional scale, reflecting either less dispersal than is often assumed or reduced establishment success of immigrants, so that dispersal does not translate into gene flow.
authors.affiliation: Laboratory of Protistology and Aquatic Ecology, Ghent University, Krijgslaan 281 - S8, Gent, 9000, Belgium.
authors.forename: Pieter
authors.initials: P
authors.lastname: Vanormelingen
authors.affiliation: School of Geosciences, University of Edinburgh, Edinburgh, EH9 3JW, UK.|Royal Botanic Garden, Edinburgh, EH3 5LR, UK.
authors.forename: Katharine M
authors.initials: KM
authors.lastname: Evans
authors.affiliation: Royal Botanic Garden, Edinburgh, EH3 5LR, UK.|Aquatic Ecosystems, Institute for Food and Agricultural Research and Technology (IRTA), Crta de Poble Nou Km 5.5, E-43540, Sant Carles de la Ràpita, Catalunya, Spain.
authors.forename: David G
authors.initials: DG
authors.lastname: Mann
authors.affiliation: Savannah River Ecology Laboratory, University of Georgia, Aiken, SC, USA.
authors.forename: Stacey
authors.initials: S
authors.lastname: Lance
authors.affiliation: Laboratory of Protistology and Aquatic Ecology, Ghent University, Krijgslaan 281 - S8, Gent, 9000, Belgium.
authors.forename: Ann-Eline
authors.initials: AE
authors.lastname: Debeer
authors.affiliation: Laboratory of Protistology and Aquatic Ecology, Ghent University, Krijgslaan 281 - S8, Gent, 9000, Belgium.
authors.forename: Sofie
authors.initials: S
authors.lastname: D'Hondt
authors.affiliation: Laboratory of Protistology and Aquatic Ecology, Ghent University, Krijgslaan 281 - S8, Gent, 9000, Belgium.
authors.forename: Tine
authors.initials: T
authors.lastname: Verstraete
authors.affiliation: Laboratory of Aquatic Ecology, Evolution and Conservation, Katholieke Universiteit Leuven, Ch. De Bériotstraat 32, Leuven, 3000, Belgium.
authors.forename: Luc
authors.initials: L
authors.lastname: De Meester
authors.affiliation: Laboratory of Protistology and Aquatic Ecology, Ghent University, Krijgslaan 281 - S8, Gent, 9000, Belgium.
authors.forename: Wim
authors.initials: W
authors.lastname: Vyverman
mesh_terms: D017377:Diatoms / Q000145:classification / Q000235:genetics*; D005060:Europe; D005618:Fresh Water; D014644:Genetic Variation; D005828:Genetics, Population; D005838:Genotype; D006239:Haplotypes; D018895:Microsatellite Repeats; D008969:Molecular Sequence Data; D017422:Sequence Analysis, DNA
keywords: Eunotia bilunaris ‘robust’; Sellaphora capitata; benthic diatoms; genotypic diversity; microsatellites; ponds; population differentiation; rbcL