title: Local Environmental Conditions Shape Generalist But Not Specialist Components of Microbial Metacommunities in the Baltic Sea.
abstract: Marine microbes exhibit biogeographical patterns linked with fluxes of matter and energy. Yet, knowledge of the mechanisms shaping bacterioplankton community assembly across temporal scales remains poor. We examined bacterioplankton 16S rRNA gene fragments obtained from Baltic Sea transects to determine phylogenetic relatedness and assembly processes coupled with niche breadth. Communities were phylogenetically more related over time than expected by chance, albeit with considerable temporal variation. Hence, habitat filtering, i.e., local environmental conditions, rather than competition structured bacterioplankton communities in summer but not in spring or autumn. Species sorting (SS) was the dominant assembly process, but temporal and taxonomical variation in mechanisms was observed. For May communities, Cyanobacteria, Actinobacteria, Alpha- and Betaproteobacteria exhibited SS while Bacteroidetes and Verrucomicrobia were assembled by SS and mass effect. Concomitantly, Gammaproteobacteria were assembled by the neutral model and patch dynamics. Temporal variation in habitat filtering and dispersal highlights the impact of seasonally driven reorganization of microbial communities. Typically abundant Baltic Sea populations such as the NS3a marine group (Bacteroidetes) and the SAR86 and SAR11 clade had the highest niche breadth. The verrucomicrobialSpartobacteriapopulation also exhibited high niche breadth. Surprisingly, variation in bacterioplankton community composition was regulated by environmental factors for generalist taxa but not specialists. Our results suggest that generalists such as NS3a, SAR86, and SAR11 are reorganized to a greater extent by changes in the environment compared to specialists and contribute more strongly to determining overall biogeographical patterns of marine bacterial communities.
authors.affiliation: Centre for Ecology and Evolution in Microbial Model Systems, Linnaeus University Kalmar, Sweden.
authors.forename: Markus V
authors.initials: MV
authors.lastname: Lindh
authors.affiliation: Centre for Ecology and Evolution in Microbial Model Systems, Linnaeus University Kalmar, Sweden.
authors.forename: Johanna
authors.initials: J
authors.lastname: Sjöstedt
authors.affiliation: Department of Aquatic Resources, Institute of Marine Research, Swedish University of Agricultural Sciences (SLU) Lysekil, Sweden.
authors.forename: Michele
authors.initials: M
authors.lastname: Casini
authors.affiliation: Department of Ecology and Environmental Science, Umeå University Umeå, Sweden.
authors.forename: Agneta
authors.initials: A
authors.lastname: Andersson
authors.affiliation: Centre for Ecology and Evolution in Microbial Model Systems, Linnaeus University Kalmar, Sweden.
authors.forename: Catherine
authors.initials: C
authors.lastname: Legrand
authors.affiliation: Centre for Ecology and Evolution in Microbial Model Systems, Linnaeus University Kalmar, Sweden.
authors.forename: Jarone
authors.initials: J
authors.lastname: Pinhassi
keywords: assembly mechanism; generalist; habitat filtering; metacommunity; net relatedness index; niche breadth; specialist