Linking transcriptional responses to organismal tolerance reveals mechanisms of thermal sensitivity in a mesothermal endangered fish.
Forecasting species' responses to climate change requires understanding the underlying mechanisms governing environmental stress tolerance, including acclimation capacity and acute stress responses. Current knowledge of these physiological processes in aquatic ectotherms is largely drawn from eurythermal or extreme stenothermal species. Yet many species of conservation concern exhibit tolerance windows and acclimation capacities in between these extremes. We linked transcriptome profiles to organismal tolerance in a mesothermal endangered fish, the delta smelt (Hypomesus transpacificus), to quantify the cellular processes, sublethal thresholds and effects of thermal acclimation on acute stress responses. Delta smelt initiated rapid molecular changes in line with expectations of theoretical thermal limitation models, but also exhibited diminished capacity to modify the expression of some genes and cellular mechanisms key to coping with acute thermal stress found in eurytherms. Sublethal critical thresholds occurred 4-6 °C below their upper tolerance limits, and thermal acclimation shifted the onset of acute thermal stress and tolerance as predicted. However, we found evidence that delta smelt's limited thermal plasticity may be partially due to an inability of individuals to effectively make physiological adjustments to truly achieve new homoeostasis under heightened temperatures, resulting in chronic thermal stress. These findings provide insight into the physiological basis of the diverse patterns of thermal tolerances observed in nature. Moreover, understanding how underlying molecular mechanisms shape thermal acclimation capacity, acute stress responses and ultimately differential phenotypes contributes to a predictive framework to deduce species' responses in situ to changes in selective pressures due to climate change.
National Research Council under contract to Southwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, 8901 La Jolla Shores Drive, La Jolla, CA, 92037, USA.|Wildlife, Fish & Conservation Biology, University of California, One Shields Avenue, Davis, CA, 95616, USA.|Anatomy, Physiology & Cell Biology, School of Veterinary Medicine, University of California, One Shields Avenue, Davis, CA, 95616, USA.
Lisa M
LM
Komoroske
Anatomy, Physiology & Cell Biology, School of Veterinary Medicine, University of California, One Shields Avenue, Davis, CA, 95616, USA.
Richard E
RE
Connon
Wildlife, Fish & Conservation Biology, University of California, One Shields Avenue, Davis, CA, 95616, USA.|Anatomy, Physiology & Cell Biology, School of Veterinary Medicine, University of California, One Shields Avenue, Davis, CA, 95616, USA.
Ken M
KM
Jeffries
Wildlife, Fish & Conservation Biology, University of California, One Shields Avenue, Davis, CA, 95616, USA.
Nann A
NA
Fangue
D000064:Acclimatization / Q000235:genetics*; D000818:Animals; D057231:Climate Change; D056727:Endangered Species; D018869:Heat-Shock Response / Q000235:genetics*; D007814:Larva / Q000235:genetics / Q000502:physiology; D008969:Molecular Sequence Data; D036441:Osmeriformes / Q000235:genetics* / Q000502:physiology; D013312:Stress, Physiological; D013696:Temperature; D059467:Transcriptome
cellular stress response; climate change; fish; phenotypic plasticity; thermal stress; transcriptomics