title: Transcriptional profiling of predator-induced phenotypic plasticity in Daphnia pulex.
abstract: BACKGROUND
  Predator-induced defences are a prominent example of phenotypic plasticity found from single-celled organisms to vertebrates. The water flea Daphnia pulex is a very convenient ecological genomic model for studying predator-induced defences as it exhibits substantial morphological changes under predation risk. Most importantly, however, genetically identical clones can be transcriptionally profiled under both control and predation risk conditions and be compared due to the availability of the sequenced reference genome. Earlier gene expression analyses of candidate genes as well as a tiled genomic microarray expression experiment have provided insights into some genes involved in predator-induced phenotypic plasticity. Here we performed the first RNA-Seq analysis to identify genes that were differentially expressed in defended vs. undefended D. pulex specimens in order to explore the genetic mechanisms underlying predator-induced defences at a qualitatively novel level.
  
  
  RESULTS
  We report 230 differentially expressed genes (158 up- and 72 down-regulated) identified in at least two of three different assembly approaches. Several of the differentially regulated genes belong to families of paralogous genes. The most prominent classes amongst the up-regulated genes include cuticle genes, zinc-metalloproteinases and vitellogenin genes. Furthermore, several genes from this group code for proteins recruited in chromatin-reorganization or regulation of the cell cycle (cyclins). Down-regulated gene classes include C-type lectins, proteins involved in lipogenesis, and other families, some of which encode proteins with no known molecular function.
  
  
  CONCLUSIONS
  The RNA-Seq transcriptome data presented in this study provide important insights into gene regulatory patterns underlying predator-induced defences. In particular, we characterized different effector genes and gene families found to be regulated in Daphnia in response to the presence of an invertebrate predator. These effector genes are mostly in agreement with expectations based on observed phenotypic changes including morphological alterations, i.e., expression of proteins involved in formation of protective structures and in cuticle strengthening, as well as proteins required for resource re-allocation. Our findings identify key genetic pathways associated with anti-predator defences.
authors.affiliation: Department of Animal Ecology, Evolution and Biodiversity, Ruhr University Bochum, Universitaetsstrasse 150, Bochum, 44801 Germany.
authors.forename: Andrey
authors.initials: A
authors.lastname: Rozenberg
authors.affiliation: Departments of Biology and Pediatrics and the Roy J. Carver Center for Genomics, 459 Biology Building, University of Iowa, Iowa City, IA 52242 USA.
authors.forename: Mrutyunjaya
authors.initials: M
authors.lastname: Parida
authors.affiliation: Department of Animal Ecology, Evolution and Biodiversity, Ruhr University Bochum, Universitaetsstrasse 150, Bochum, 44801 Germany.|Present address: University of Duisburg-Essen, Aquatic Ecosystems Research, Universitaetsstrasse 5, Essen, 45141 Germany.
authors.forename: Florian
authors.initials: F
authors.lastname: Leese
authors.affiliation: Department of Animal Ecology, Evolution and Biodiversity, Ruhr University Bochum, Universitaetsstrasse 150, Bochum, 44801 Germany.|Environmental Genomics Group, School of Biosciences, University of Birmingham, Birmingham, B15 2TT UK.
authors.forename: Linda C
authors.initials: LC
authors.lastname: Weiss
authors.affiliation: Department of Animal Ecology, Evolution and Biodiversity, Ruhr University Bochum, Universitaetsstrasse 150, Bochum, 44801 Germany.
authors.forename: Ralph
authors.initials: R
authors.lastname: Tollrian
authors.affiliation: Departments of Biology and Pediatrics and the Roy J. Carver Center for Genomics, 459 Biology Building, University of Iowa, Iowa City, IA 52242 USA.
authors.forename: J Robert
authors.initials: JR
authors.lastname: Manak
keywords: Daphnia; Gene-environment interactions; Inducible defences; Morphology; Phenotypic plasticity; Predator-prey interaction; RNA-Seq; Transcriptomics