title: Plasticity of protective mechanisms only partially explains interactive effects of temperature and UVR on upper thermal limits.
abstract: Temperature and ultraviolet radiation (UVR) are key environmental drivers that are linked in their effects on cellular damage. Exposure to both high temperatures and UVR can cause cellular damage that result in the up-regulation of common protective mechanisms, such as the induction of heat shock proteins (Hsps) and antioxidants. As such, the interactive effects of these stressors at the cellular level may determine physiological limits, such as thermal tolerance. Furthermore, antioxidant activity is often thermally sensitive, which may lead to temperature dependent effects of UVR exposure. Here we examined the interactive effects of temperature and UVR on upper thermal limits, Hsp70 abundance, oxidative damage and antioxidant (catalase) activity. We exposed Limnodynastes peronii tadpoles to one of three temperature treatments (constant 18°C, constant 28°C and daily fluctuations between 18 and 28°C) in the presence or absence of UVR. Tadpoles were tested for upper thermal limits (CTmax), induction of Hsp70, oxidative damage and catalase activity. Our results show that CTmax was influenced by an interactive effect between temperature and UVR treatment. For tadpoles kept in cold temperatures, exposure to UVR led to cross-tolerance to high temperatures, increasing CTmax. Plasticity in this trait was not fully explained by changes in the lower level mechanistic traits examined. These results highlight the difficulty in predicting the mechanistic basis for the interactive effects of multiple stressors on whole animal traits. Multifactorial studies may therefore be required to understand how complex mechanistic processes shape physiological tolerances, and determine responses to environmental variation.
authors.affiliation: School of Biological Sciences, The University of QLD, Brisbane 4072, Australia. Electronic address: pippa.kern@uqconnect.edu.au.
authors.forename: Pippa
authors.initials: P
authors.lastname: Kern
authors.affiliation: School of Biological Sciences, The University of QLD, Brisbane 4072, Australia.
authors.forename: Rebecca L
authors.initials: RL
authors.lastname: Cramp
authors.affiliation: School of Biological Science, The University of Sydney, Sydney 2006, Australia.
authors.forename: Frank
authors.initials: F
authors.lastname: Seebacher
authors.affiliation: School of Biological Science, The University of Sydney, Sydney 2006, Australia.
authors.forename: Ensiyeh
authors.initials: E
authors.lastname: Ghanizadeh Kazerouni
authors.affiliation: School of Biological Sciences, The University of QLD, Brisbane 4072, Australia.
authors.forename: Craig E
authors.initials: CE
authors.lastname: Franklin
mesh_terms: D000222:Adaptation, Physiological / Q000528:radiation effects; D029845:Amphibian Proteins / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001001:Anura / Q000254:growth & development / Q000502:physiology*; D002374:Catalase / Q000235:genetics / Q000378:metabolism; D000066670:Cell Plasticity / Q000528:radiation effects; D018507:Gene Expression Regulation, Developmental / Q000528:radiation effects; D050884:HSP72 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D006358:Hot Temperature / Q000009:adverse effects; D007814:Larva / Q000254:growth & development / Q000502:physiology / Q000528:radiation effects; D015227:Lipid Peroxidation / Q000528:radiation effects; D008954:Models, Biological; D018384:Oxidative Stress / Q000528:radiation effects; D050050:Protein Carbonylation / Q000528:radiation effects; D011793:Queensland; D011897:Random Allocation; D013312:Stress, Physiological / Q000528:radiation effects; D016019:Survival Analysis; D013997:Time Factors; D014466:Ultraviolet Rays / Q000009:adverse effects
chemical_list: D029845:Amphibian Proteins; D050884:HSP72 Heat-Shock Proteins; D002374:Catalase
keywords: CTmax; Fluctuating temperatures; Heat shock proteins; Interaction; Multifactorial; Oxidative damage; Physiological tolerance; Stressors; Tadpole