title: Weak Coherence in Abundance Patterns Between Bacterial Classes and Their Constituent OTUs Along a Regulated River.
abstract: Deductions about the ecology of high taxonomic bacterial ranks (i.e., phylum, class, order) are often based on their abundance patterns, yet few studies have quantified how accurately variations in abundance of these bacterial groups represent the dynamics of the taxa within them. Using 454-pyrosequencing of the 16S rRNA gene, we investigated whether the changes in abundance of six dominant bacterial classes (Actinobacteria, Beta-/Alpha-/Gamma-proteobacteria, Flavobacteria, and Sphingobacteria) along a large dam-regulated river are reflected by those of their constituent Operational Taxonomic Units (OTUs; 97% similarity level). The environmental impact generated by the reservoirs promoted clear compositional shifts in all bacterial classes that resulted from changes in the abundance of individual OTUs rather than from the appearance of new taxa along the river. Abundance patterns at the class level represented the dynamics of only a small but variable proportion of their constituting OTUs, which were not necessarily the most abundant ones. Within most classes, we detected sub-groups of OTUs showing contrasting responses to reservoir-induced environmental changes. Overall, we show that the patterns observed at the class level fail to capture the dynamics of a significant fraction of their constituent members, calling for caution when the ecological attributes of high-ranks are to be interpreted.
authors.affiliation: Institute of Aquatic Ecology, University of Girona Girona, Spain ; Departament de Biologia Marina i Oceanografia, Institut de Ciències del Mar (ICM-CSIC) Barcelona, Spain ; Département des Sciences Biologiques, Université du Québec à Montréal Montréal, QC, Canada.
authors.forename: Clara
authors.initials: C
authors.lastname: Ruiz-González
authors.affiliation: Departament de Biologia Marina i Oceanografia, Institut de Ciències del Mar (ICM-CSIC) Barcelona, Spain.
authors.forename: Guillem
authors.initials: G
authors.lastname: Salazar
authors.affiliation: Departament de Biologia Marina i Oceanografia, Institut de Ciències del Mar (ICM-CSIC) Barcelona, Spain.
authors.forename: Ramiro
authors.initials: R
authors.lastname: Logares
authors.affiliation: Institute of Aquatic Ecology, University of Girona Girona, Spain ; Catalan Institute for Water Research, Scienfitic and Technological Parc of the University of Girona Girona, Spain.
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Proia
authors.affiliation: Departament de Biologia Marina i Oceanografia, Institut de Ciències del Mar (ICM-CSIC) Barcelona, Spain.
authors.forename: Josep M
authors.initials: JM
authors.lastname: Gasol
authors.affiliation: Institute of Aquatic Ecology, University of Girona Girona, Spain ; Catalan Institute for Water Research, Scienfitic and Technological Parc of the University of Girona Girona, Spain.
authors.forename: Sergi
authors.initials: S
authors.lastname: Sabater
keywords: 454-pyrosequencing; bacterial community composition; ecological coherence; freshwater bacterioplankton; high-rank lineages; river gradient