title: Warm preconditioning protects against acute heat-induced respiratory dysfunction and delays bleaching in a symbiotic sea anemone.
abstract: Preconditioning to non-stressful warming can protect some symbiotic cnidarians against the high temperature-induced collapse of their mutualistic endosymbiosis with photosynthetic dinoflagellates (Symbiodiniumspp.), a process known as bleaching. Here, we sought to determine whether such preconditioning is underpinned by differential regulation of aerobic respiration. We quantifiedin vivometabolism and mitochondrial respiratory enzyme activity in the naturally symbiotic sea anemoneExaiptasia pallidapreconditioned to 30°C for >7 weeks as well as anemones kept at 26°C. Preconditioning resulted in increasedSymbiodiniumphotosynthetic activity and holobiont (host+symbiont) respiration rates. Biomass-normalised activities of host respiratory enzymes [citrate synthase and the mitochondrial electron transport chain (mETC) complexes I and IV] were higher in preconditioned animals, suggesting that increased holobiont respiration may have been due to host mitochondrial biogenesis and/or enlargement. Subsequent acute heating of preconditioned and 'thermally naive' animals to 33°C induced dramatic increases in host mETC complex I andSymbiodiniummETC complex II activities only in thermally naiveE. pallidaThese changes were not reflected in the activities of other respiratory enzymes. Furthermore, bleaching in preconditionedE. pallida(defined as the significant loss of symbionts) was delayed by several days relative to the thermally naive group. These findings suggest that changes to mitochondrial biogenesis and/or function in symbiotic cnidarians during warm preconditioning might play a protective role during periods of exposure to stressful heating.
authors.affiliation: School of Marine Science and Policy, College of Earth, Ocean and Environment, University of Delaware, 700 Pilottown Road, Lewes, DE 19958, USA tom.hawkins.photo@gmail.com mwarner@udel.edu.
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Hawkins
authors.affiliation: School of Marine Science and Policy, College of Earth, Ocean and Environment, University of Delaware, 700 Pilottown Road, Lewes, DE 19958, USA tom.hawkins.photo@gmail.com mwarner@udel.edu.
authors.forename: Mark E
authors.identifier: 0000-0003-1015-9413
authors.initials: ME
authors.lastname: Warner
mesh_terms: D000064:Acclimatization; D000818:Animals; D004141:Dinoflagellida / Q000201:enzymology / Q000502:physiology*; D018869:Heat-Shock Response; D006358:Hot Temperature; D008928:Mitochondria / Q000201:enzymology / Q000378:metabolism; D010101:Oxygen Consumption; D010788:Photosynthesis; D012615:Sea Anemones / Q000201:enzymology / Q000502:physiology*; D013559:Symbiosis
keywords: Acclimation; Aiptasia; Cnidarian–dinoflagellate symbiosis; Coral bleaching; Exaiptasia pallida; Respiration; Thermal stress