title: Predator-prey interactions in a changing world: humic stress disrupts predator threat evasion in copepods.
abstract: Increasing inputs of colored dissolved organic matter (cDOM), which is mainly composed of humic substances (HS), are a widespread phenomenon of environmental change in aquatic ecosystems. This process of brownification alters the chemical conditions of the environment, but knowledge is lacking of whether elevated cDOM and HS levels interfere with the ability of prey species to evade chemical predator cues and thus affect predator-prey interactions. We assessed the effects of acute and prolonged exposure to HS at increasing concentrations on the ability of freshwater zooplankton to avoid predator threat (imposed by fish kairomones) in laboratory trials with two calanoid copepods (Eudiaptomus gracilis and Heterocope appendiculata). Populations of both species clearly avoided water containing fish kairomones. However, the avoidance behavior weakened with increasing HS concentration, suggesting that HS affected the ability of copepods to perceive or respond to the predator cue. The behavioral responses of the two copepod populations to increasing HS concentrations differed, with H. appendiculata being more sensitive than E. gracilis in an acute exposure scenario, whereas E. gracilis responded more strongly after prolonged exposure. Both showed similar physiological impairment after prolonged exposure, as revealed by their oxidative balance as a stress indicator, but mortality increased more strongly for H. appendiculata when the HS concentration increased. These results indicate that reduced predator threat evasion in the presence of cDOM could make copepods more susceptible to predation in future, with variation in the strength of responses among populations leading to changes in zooplankton communities and lake food-web structure.
authors.affiliation: Institut Méditerranéen de Biodiversité et d'Ecologie (IMBE), Aix Marseille Université, CNRS, IRD, Avignon Université, CS 80249, Case 4, 13331, Marseille Cedex 03, France. mathieu.santonja@gmail.com.|Université Rennes 1, UMR CNRS 6553 ECOBIO, Avenue du Général Leclerc, Campus de Beaulieu, 35042, Rennes, France. mathieu.santonja@gmail.com.
authors.forename: Mathieu
authors.identifier: 0000-0002-6322-6352
authors.initials: M
authors.lastname: Santonja
authors.affiliation: Department Experimental Limnology, Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB), Alte Fischerhütte 2, 16775, Stechlin, Germany.
authors.forename: Laetitia
authors.initials: L
authors.lastname: Minguez
authors.affiliation: Department Experimental Limnology, Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB), Alte Fischerhütte 2, 16775, Stechlin, Germany.|Department of Ecology, Berlin Institute of Technology (TU Berlin), Ernst-Reuter-Platz 1, 10587, Berlin, Germany.|Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), 14195, Berlin, Germany.
authors.forename: Mark O
authors.initials: MO
authors.lastname: Gessner
authors.affiliation: Department Experimental Limnology, Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB), Alte Fischerhütte 2, 16775, Stechlin, Germany. eriksperfeld@googlemail.com.|Department of Biosciences, Centre for Ecological and Evolutionary Synthesis (CEES), University of Oslo, PO Box 1066, Blindern, 0316, Oslo, Norway. eriksperfeld@googlemail.com.
authors.forename: Erik
authors.initials: E
authors.lastname: Sperfeld
mesh_terms: D000818:Animals; D033342:Copepoda; D020387:Food Chain; D005618:Fresh Water / Q000737:chemistry; D011235:Predatory Behavior; D015048:Zooplankton
keywords: Brownification; Chemical ecology; Global change; Humic substances; Zooplankton behavior