Responses of Eastern red-backed salamanders (Plethodon cinereus) to chemical cues of prey presented in soluble and volatile forms

Assessing predator-prey interactions in a chemically altered aquatic environment: the effects of DDT on Xenopus laevis and Culex sp. larvae interactions and behaviour

Behavioural assays are used as a tool to understand ecotoxicological effects on organisms, but are often not applied in an ecologically relevant context. Assessment of the effect of chemical contaminants on behaviours relating to fitness and trophic interactions for example, requires incorporating predator-prey interactions to create impact assessments. Dichlorodiphenyltrichloroethane (DDT) is a controlled substance but is still regularly used as a form of mosquito control. There is little explicit information on the effect of DDT on animal behaviour and the consequent effects upon trophic interactions. This study uses a 3 × 2 factorial design to assess the feeding behaviour of Xenopus laevis toward Culex sp. larvae when supplied with different prey cues. We also assess the behavioural responses of mosquito larvae when supplied with no threat cue and predator threat cues when exposed to 0 µg/L, 2 µg/L and 20 µg/L DDT. There was a significant "DDT exposure" x "prey cue" interaction whereby DDT significantly decreased the foraging behaviour of X. laevis towards live prey cues, however there was no effect of DDT on X. laevis response to olfactory prey cues. Dichlorodiphenyltrichloroethane exposure caused mosquito larvae to appear hyperactive regardless of DDT concentration. Mosquito larvae anti-predator response was significantly dampened when exposed to 2 µg/L DDT, however when exposed to 20 µg/L the anti-predator responses were not impaired. Our results indicate a complex interplay in trophic interactions under DDT exposure, wherein effects are mediated depending on species and concentration. There are possible implications regarding reduced anti-predator behaviour in the prey species but also reduced foraging capacity in the predator, which could drive changes in ecosystem energy pathways. We demonstrate that in order to quantify effects of pesticides upon trophic interactions it is necessary to consider ecologically relevant behaviours of both predator and prey species.

A test of scent-trailing as a contributing factor in the climbing behaviour of the redback salamander (Plethodon cinereus)

Terrestrial salamanders of the family Plethodontidae are common predators of invertebrates in deciduous forest communities of eastern North America. While normally residing and foraging in forest-floor microhabitats, many species facultatively climb vegetation. Different hypotheses have been proffered to explain this behaviour including optimal-foraging strategies and predator avoidance. Using laboratory-based trials, we tested the hypothesis that the terrestrial salamander Plethodon cinereus climbs in response to scent trails left by insect prey. We found that salamanders climbed significantly higher and spent significantly more time climbing on wooden dowel rods that had been treated with prey residue than they did on control rods. Scent trailing possibly interacts with other factors such as optimal-foraging opportunities and predation risk in influencing climbing behaviour in these salamanders.