title: Combined effect of temperature and ammonia on molecular response and survival of the freshwater crustacean Gammarus pulex.
abstract: Freshwater ecosystems are experiencing mounting pressures from agriculture, urbanization, and climate change, which could drastically impair aquatic biodiversity. As nutrient inputs increase and temperatures rise, ammonia (NH3) concentration is likely to be associated with stressful temperatures. To investigate the interaction between NH3and temperature on aquatic invertebrate survival, we performed a factorial experiment on the survival and molecular response of Gammarus pulex, with temperature (10, 15, 20, and 25°C) and NH3(0, 0.5, 1, 2, 3, and 4mg NH3/L) treatments. We observed an unexpected antagonistic interaction between temperature and NH3concentration, meaning survival in the 4mg NH3/L treatment was higher at 25°C than at the control temperature of 10°C. A toxicokinetic-toxicodynamic (TK-TD) model was built to describe this antagonistic interaction. While the No Effect Concentration showed no significant variation across temperatures, the 50% lethal concentration at the end of the experiment increased from 2.7 (2.1-3.6) at 10°C to 5.5 (3.5- 23.4) mg NH3/L at 25°C. Based on qPCR data, we associated these survival patterns to variations in the expression of the hsp70 gene, a generic biomarker of stress. However, though there was a 14-fold increase in hsp70 mRNA expression for gammarids exposed to 25°C compared to controls, NH3concentration had no effect on hsp70 mRNA synthesis across temperatures. Our results demonstrate that the effects of combined environmental stressors, like temperature and NH3, may strongly differ from simple additive effects, and that stress response to temperature can actually increase resilience to nutrient pollution in some circumstances.
authors.affiliation: Université Rennes 1, UMR CNRS 6553 Ecobio, 263 avenue du Général Leclerc, CS 74205, 35042 Rennes Cedex, France. Electronic address: henry.youn@orange.fr.
authors.forename: Y
authors.initials: Y
authors.lastname: Henry
authors.affiliation: Université Rennes 1, UMR CNRS 6553 Ecobio, 263 avenue du Général Leclerc, CS 74205, 35042 Rennes Cedex, France. Electronic address: christophe.piscart@univ-rennes1.fr.
authors.forename: C
authors.initials: C
authors.lastname: Piscart
authors.affiliation: Univ Lyon, Université Lyon 1, UMR CNRS 5558, Laboratoire de Biométrie et Biologie Évolutive, F-69100 Villeurbanne, France.
authors.forename: S
authors.initials: S
authors.lastname: Charles
authors.affiliation: Université Rennes 1, UMR CNRS 6553 Ecobio, 263 avenue du Général Leclerc, CS 74205, 35042 Rennes Cedex, France.
authors.forename: H
authors.initials: H
authors.lastname: Colinet
mesh_terms: D000641:Ammonia / Q000633:toxicity*; D033304:Amphipoda / Q000187:drug effects* / Q000378:metabolism; D000818:Animals; D057231:Climate Change; D004784:Environmental Monitoring; D005602:France; D005618:Fresh Water / Q000737:chemistry*; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism*; D006358:Hot Temperature; D008962:Models, Theoretical; D018384:Oxidative Stress / Q000187:drug effects; D016019:Survival Analysis; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D018840:HSP70 Heat-Shock Proteins; D014874:Water Pollutants, Chemical; D000641:Ammonia
keywords: Antagonism; Heat shock proteins; Multi-stress; TK-TD models