title: Synergistic interactions of biotic and abiotic environmental stressors on gene expression.
abstract: Understanding the response of organisms to multiple stressors is critical for predicting if populations can adapt to rapid environmental change. Natural and anthropogenic stressors often interact, complicating general predictions. In this study, we examined the interactive and cumulative effects of two common environmental stressors, lowered calcium concentration, an anthropogenic stressor, and predator presence, a natural stressor, on the water flea Daphnia pulex. We analyzed expression changes of five genes involved in calcium homeostasis - cuticle proteins (Cutie, Icp2), calbindin (Calb), and calcium pump and channel (Serca and Ip3R) - using real-time quantitative PCR (RT-qPCR) in a full factorial experiment. We observed strong synergistic interactions between low calcium concentration and predator presence. While the Ip3R gene was not affected by the stressors, the other four genes were affected in their transcriptional levels by the combination of the stressors. Transcriptional patterns of genes that code for cuticle proteins (Cutie and Icp2) and a sarcoplasmic calcium pump (Serca) only responded to the combination of stressors, changing their relative expression levels in a synergistic response, while a calcium-binding protein (Calb) responded to low calcium stress and the combination of both stressors. The expression pattern of these genes (Cutie, Icp2, and Serca) were nonlinear, yet they were dose dependent across the calcium gradient. Multiple stressors can have complex, often unexpected effects on ecosystems. This study demonstrates that the dominant interaction for the set of tested genes appears to be synergism. We argue that gene expression patterns can be used to understand and predict the type of interaction expected when organisms are exposed simultaneously to natural and anthropogenic stressors.
authors.affiliation: a Department of Biology, McGill University, Montreal, Canada.
authors.forename: Ianina
authors.initials: I
authors.lastname: Altshuler
authors.affiliation: b Great Lakes Institute for Environmental Research, University of Windsor, Windsor, Ontario, Canada.
authors.forename: Anne M
authors.initials: AM
authors.lastname: McLeod
authors.affiliation: c Department of Biology, Birmingham University, England.
authors.forename: John K
authors.initials: JK
authors.lastname: Colbourne
authors.affiliation: d Department of Biology, York University, Toronto, Ontario, Canada.
authors.forename: Norman D
authors.initials: ND
authors.lastname: Yan
authors.affiliation: a Department of Biology, McGill University, Montreal, Canada.
authors.forename: Melania E
authors.initials: ME
authors.lastname: Cristescu
mesh_terms: D000818:Animals; D064026:Calbindins / Q000235:genetics; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling; D003621:Daphnia / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D006706:Homeostasis; D013312:Stress, Physiological
chemical_list: D064026:Calbindins; D002118:Calcium
keywords: Daphnia pulex; anthropogenic stressors; biotic stressors; calcium level; expression génique; gene expression; kairomones de prédateurs; niveau de calcium; predator kairomones; stress anthropogéniques; stress biotiques