title: Transcriptomic responses to seawater acidification among sea urchin populations inhabiting a natural pH mosaic.
abstract: Increasing awareness of spatial and temporal variation in ocean pH suggests some marine populations may be adapted to local pH regimes and will therefore respond differently to present-day pH variation and to long-term ocean acidification. In the Northeast Pacific Ocean, differences in the strength of coastal upwelling cause latitudinal variation in prevailing pH regimes that are hypothesized to promote local adaptation and unequal pH tolerance among resident populations. In this study, responses to experimental seawater acidification were compared among embryos and larvae from six populations of purple sea urchins (Strongylocentrotus purpuratus) inhabiting areas that differ in their frequency of low pH exposure and that prior research suggests are locally adapted to seawater pH. Transcriptomic analyses demonstrate urchin populations most frequently exposed to low pH seawater responded to experimental acidification by expressing genes within major ATP-producing pathways at greater levels than populations encountering low pH less often. Multiple genes within the tricarboxylic acid cycle, electron transport chain and fatty acid beta oxidation pathways were upregulated in urchin populations experiencing low pH conditions most frequently. These same metabolic pathways were significantly over-represented among genes both expressed in a population-specific manner and putatively under selection to enhance low pH tolerance. Collectively, these data suggest natural selection is acting on metabolic gene networks to redirect ATP toward maintaining acid-base homeostasis and enhance tolerance of seawater acidification. As a trade-off, marine populations more tolerant of low pH may have less energy to put towards other aspects of fitness and to respond to additional ocean change.
authors.affiliation: Department of Biological Sciences, California State University East Bay, Hayward, CA, 94542, USA.
authors.forename: Tyler G
authors.identifier: http://orcid.org/0000-0003-0329-5919
authors.initials: TG
authors.lastname: Evans
authors.affiliation: Department of Biology, University of Vermont, Burlington, VT, 05405, USA.
authors.forename: Melissa H
authors.initials: MH
authors.lastname: Pespeni
authors.affiliation: Department of Ecology, Evolution and Marine Biology, University of California Santa Barbara, Santa Barbara, CA, 93106, USA.
authors.forename: Gretchen E
authors.initials: GE
authors.lastname: Hofmann
authors.affiliation: Department of Biology, Stanford University, Hopkins Marine Station, Pacific Grove, CA, 93950, USA.
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Palumbi
authors.affiliation: Department of Evolution and Ecology and Bodega Marine Laboratory, University of California Davis, Bodega Bay, CA, 94923, USA.
authors.forename: Eric
authors.initials: E
authors.lastname: Sanford
mesh_terms: D000064:Acclimatization / Q000235:genetics*; D000143:Acids / Q000737:chemistry; D000818:Animals; D002245:Carbon Dioxide / Q000737:chemistry; D057231:Climate Change; D006863:Hydrogen-Ion Concentration; D010140:Pacific Ocean; D020641:Polymorphism, Single Nucleotide; D012623:Seawater / Q000737:chemistry*; D047270:Strongylocentrotus purpuratus / Q000235:genetics*; D059467:Transcriptome
chemical_list: D000143:Acids; D002245:Carbon Dioxide
keywords: climate change; genomics; ocean acidification; population; transcriptomics; urchin