title: Low levels of chemical anthropogenic pollution may threaten amphibians by impairing predator recognition.
abstract: Recent studies suggest that direct mortality and physiological effects caused by pollutants are major contributing factors to global amphibian decline. However, even sublethal concentrations of pollutants could be harmful if they combined with other factors to cause high mortality in amphibians. Here we show that sublethal concentrations of pollutants can disrupt the ability of amphibian larvae to recognize predators, hence increasing their risk of predation. This effect is indeed much more important since very low amounts of pollutants are ubiquitous, and environmental efforts are mostly directed towards preventing lethal spills. We analyzed the effects of two common contaminants (humic acid and ammonium nitrate) on the ability of tadpoles of the western spadefoot toad (Pelobates cultripes) to recognize chemical cues from a common predator, nymphs of the dragonfly Anax imperator. We compared the swimming activity of tadpoles in the presence and absence of water-borne chemical cues from dragonflies at different concentrations of humic acid and ammonium nitrate. Tadpoles reduced swimming activity in response to predator cues in the absence of pollutants, whereas they remained unresponsive to these cues when either humic acid or ammonium nitrate was added to the water, even at low concentrations. Moreover, changes in tadpole activity associated with the pollutants themselves were non-significant, indicating no toxic effect. Alteration of the natural chemical environment of aquatic systems by pollutants may be an important contributing cause for declines in amphibian populations, even at sublethal concentrations.
authors.affiliation: Department of Biology, Universidad Autónoma de Madrid, 28049 Madrid, Spain. Electronic address: nuria.polo@uam.es.
authors.forename: Nuria
authors.initials: N
authors.lastname: Polo-Cavia
authors.affiliation: Ecology, Evolution, and Development Group, Department of Wetland Ecology, Doñana Biological Station, CSIC, E-41092 Seville, Spain.
authors.forename: Pablo
authors.initials: P
authors.lastname: Burraco
authors.affiliation: Ecology, Evolution, and Development Group, Department of Wetland Ecology, Doñana Biological Station, CSIC, E-41092 Seville, Spain. Electronic address: igmestre@ebd.csic.es.
authors.forename: Ivan
authors.initials: I
authors.lastname: Gomez-Mestre
mesh_terms: D000818:Animals; D001001:Anura / Q000502:physiology*; D004781:Environmental Exposure; D006812:Humic Substances / Q000633:toxicity; D007814:Larva / Q000187:drug effects; D009566:Nitrates / Q000633:toxicity; D063191:Odonata; D046709:Pattern Recognition, Physiological / Q000187:drug effects; D011235:Predatory Behavior / Q000187:drug effects*; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D006812:Humic Substances; D009566:Nitrates; D014874:Water Pollutants, Chemical; C006568:ammonium nitrate
keywords: Ammonium nitrate; Amphibians; Chemical cues; Humic acid; Predator recognition; Water pollutants