title: Effects of high temperatures on threatened estuarine fishes during periods of extreme drought.
abstract: Climate change and associated increases in water temperatures may impact physiological performance in ectotherms and exacerbate endangered species declines. We used an integrative approach to assess the impact of elevated water temperature on two fishes of immediate conservation concern in a large estuary system, the threatened longfin smelt (Spirinchus thaleichthys) and endangered delta smelt (Hypomesus transpacificus). Abundances have reached record lows in California, USA, and these populations are at imminent risk of extirpation. California is currently impacted by a severe drought, resulting in high water temperatures, conditions that will become more common as a result of climate change. We exposed fish to environmentally relevant temperatures (14°C and 20°C) and used RNA sequencing to examine the transcriptome-wide responses to elevated water temperature in both species. Consistent with having a lower temperature tolerance, longfin smelt exhibited a pronounced cellular stress response, with an upregulation of heat shock proteins, after exposure to 20°C that was not observed in delta smelt. We detected an increase in metabolic rate in delta smelt at 20°C and increased expression of genes involved in metabolic processes and protein synthesis, patterns not observed in longfin smelt. Through examination of responses across multiple levels of biological organization, and by linking these responses to habitat distributions in the wild, we demonstrate that longfin smelt may be more susceptible than delta smelt to increases in temperatures, and they have little room to tolerate future warming in California. Understanding the species-specific physiological responses of sensitive species to environmental stressors is crucial for conservation efforts and managing aquatic systems globally.
authors.affiliation: Anatomy, Physiology & Cell Biology, School of Veterinary Medicine, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA Wildlife, Fish & Conservation Biology, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA kenmjeffries@gmail.com.
authors.forename: Ken M
authors.initials: KM
authors.lastname: Jeffries
authors.affiliation: Anatomy, Physiology & Cell Biology, School of Veterinary Medicine, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA.
authors.forename: Richard E
authors.initials: RE
authors.lastname: Connon
authors.affiliation: Wildlife, Fish & Conservation Biology, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA Department of Animal Science, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA.
authors.forename: Brittany E
authors.initials: BE
authors.lastname: Davis
authors.affiliation: Anatomy, Physiology & Cell Biology, School of Veterinary Medicine, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA Wildlife, Fish & Conservation Biology, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA.
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Komoroske
authors.affiliation: Bioinformatics Core Facility, Genome Center, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA.
authors.forename: Monica T
authors.initials: MT
authors.lastname: Britton
authors.affiliation: California Department of Water Resources, Division of Environmental Services, P.O. Box 942836, Sacramento, CA 94236, USA.
authors.forename: Ted
authors.initials: T
authors.lastname: Sommer
authors.affiliation: Department of Animal Science, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA.
authors.forename: Anne E
authors.initials: AE
authors.lastname: Todgham
authors.affiliation: Wildlife, Fish & Conservation Biology, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA.
authors.forename: Nann A
authors.initials: NA
authors.lastname: Fangue
mesh_terms: D000818:Animals; D002140:California; D055864:Droughts; D056727:Endangered Species; D004777:Environment; D063366:Estuaries; D020869:Gene Expression Profiling; D063990:Gene Ontology; D036441:Osmeriformes / Q000502:physiology*; D010101:Oxygen Consumption / Q000502:physiology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013696:Temperature
chemical_list: D012333:RNA, Messenger
keywords: Delta smelt; Endangered fishes; Hypomesus transpacificus; Longfin smelt; Spirinchus thaleichthys; Transcriptomics