title: Transcriptomic imprints of adaptation to fresh water: parallel evolution of osmoregulatory gene expression in the Alewife.
abstract: Comparative approaches in physiological genomics offer an opportunity to understand the functional importance of genes involved in niche exploitation. We used populations of Alewife (Alosa pseudoharengus) to explore the transcriptional mechanisms that underlie adaptation to fresh water. Ancestrally anadromous Alewives have recently formed multiple, independently derived, landlocked populations, which exhibit reduced tolerance of saltwater and enhanced tolerance of fresh water. Using RNA-seq, we compared transcriptional responses of an anadromous Alewife population to two landlocked populations after acclimation to fresh (0 ppt) and saltwater (35 ppt). Our results suggest that the gill transcriptome has evolved in primarily discordant ways between independent landlocked populations and their anadromous ancestor. By contrast, evolved shifts in the transcription of a small suite of well-characterized osmoregulatory genes exhibited a strong degree of parallelism. In particular, transcription of genes that regulate gill ion exchange has diverged in accordance with functional predictions: freshwater ion-uptake genes (most notably, the 'freshwater paralog' of Na+/K+-ATPase α-subunit) were more highly expressed in landlocked forms, whereas genes that regulate saltwater ion secretion (e.g. the 'saltwater paralog' of NKAα) exhibited a blunted response to saltwater. Parallel divergence of ion transport gene expression is associated with shifts in salinity tolerance limits among landlocked forms, suggesting that changes to the gill's transcriptional response to salinity facilitate freshwater adaptation.
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, CT, 06269-3043, USA.
authors.forename: Jonathan P
authors.identifier: http://orcid.org/0000-0002-3100-9951
authors.initials: JP
authors.lastname: Velotta
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, CT, 06269-3043, USA.
authors.forename: Jill L
authors.initials: JL
authors.lastname: Wegrzyn
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, CT, 06269-3043, USA.
authors.forename: Samuel
authors.initials: S
authors.lastname: Ginzburg
authors.affiliation: Department of Biological Sciences, Virginia Bioinformatics Institute, Virginia Tech, Blacksburg, VA, 24061, USA.
authors.forename: Lin
authors.initials: L
authors.lastname: Kang
authors.affiliation: Lake Michigan Biological Station, Illinois Natural History Survey, University of Illinois, Zion, IL, 60099, USA.
authors.forename: Sergiusz
authors.initials: S
authors.lastname: Czesny
authors.affiliation: Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT, 06269-3125, USA.
authors.forename: Rachel J
authors.initials: RJ
authors.lastname: O'Neill
authors.affiliation: Conte Anadromous Fish Research Center, U.S. Geological Survey, Turners Falls, MA, 01376, USA.
authors.forename: Stephen D
authors.initials: SD
authors.lastname: McCormick
authors.affiliation: Department of Biological Sciences, Virginia Bioinformatics Institute, Virginia Tech, Blacksburg, VA, 24061, USA.
authors.forename: Pawel
authors.initials: P
authors.lastname: Michalak
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, CT, 06269-3043, USA.
authors.forename: Eric T
authors.initials: ET
authors.lastname: Schultz
mesh_terms: D000064:Acclimatization / Q000235:genetics*; D000818:Animals; D005399:Fishes / Q000235:genetics* / Q000502:physiology; D005618:Fresh Water; D005880:Gills / Q000502:physiology*; D012623:Seawater; D000254:Sodium-Potassium-Exchanging ATPase / Q000235:genetics; D059467:Transcriptome
chemical_list: D000254:Sodium-Potassium-Exchanging ATPase
keywords: 
  Alosa pseudoharengus
  ; Na+/K+ATPase α1 paralogs; RNA-seq; functional genomics; gene expression; gill; ion regulation; osmoregulation