Responses of American toad tadpoles to predation cues: behavioural response thresholds, threat-sensitivity and acquired predation recognition

Abstract

Predation is one of the most important selective forces acting on prey animals. To respond adaptively to predation threats and increase their chances of survival, prey animals have to be able to recognize their potential predators. Even though a few studies demonstrated innate predator recognition, the vast majority of animals have to rely on learning to acquire this information. Often aquatic prey animals can learn to recognize predators when they detect conspecific alarm cues associated with cues from a novel predator. In this study, we exposed American toad (Bufo americanus) tadpoles to varying concentrations of chemical alarm cues (cues from injured conspecifics). We identified a concentration of cues which caused an overt antipredator response (supra-threshold concentration) and a lower concentration for which the prey failed to exhibit a response (sub-threshold concentration). In a second experiment, we attempted to condition the tadpoles to recognize the odour of larval dragonflies (Anax sp.) by pairing the dragonfly odour with either the sub-threshold concentration or the supra-threshold concentration of alarm cues. In both cases, the tadpoles learned to recognize the predator based on this single pairing of alarm cues and predator odour. Moreover, the intensity of the learned response was stronger for tadpoles conditioned with the supra-threshold concentration of alarm cues than the sub-threshold concentration. This is the first documented case of this mode of learning in anuran amphibians. Learned recognition of predators has important implications for survival.

Vulnerability and behavioral responses of South Chinese anuran tadpoles to native dragonfly (Pantala flavescens) naiads and introduced western mosquitofish (Gambusia affinis)

“…Low activity state makes prey less noticeable to visually oriented predators, then may decrease the probability that prey will inadvertently swim near a visually cryptic ambush predator such as a dragonfly naiad. For aquatic vertebrates, decreased activity has been reported as a common response to increased predation risk (Mirza et al 2006), and it has been shown to increase the probability of tadpoles surviving encounters with dragonfly predators (Skelly 1994). This is also consistent with previous studies demonstrating that spatial avoidance of the predator was an instinctive response for prey (Laurila et al 1997;Nicieza et al 2006).…”

Latent inhibition of predator recognition by embryonic amphibians

“…Several learning modes allow the acquisition of predator recognition. In aquatic organisms, amphibians (Woody & Mathis 1998;Mirza et al 2006), fishes (Chivers & Smith 1994;Wisenden et al 2008) and a number of invertebrates (Hazlett 2003;) acquire predator recognition through simultaneous pairing of chemical cues from injured conspecifics with the sight, odour or sound of a novel predator.…”

Effects of embryonic exposure to conspecific chemical cues on hatching and larval traits in the common frog (Rana temporaria)

“…Only significant differences are shown: *P<0.05 effects of chemical cues from damaged conspecific tadpoles on hatching traits are highly sensitive to the amount of active substance present in the embryonic environment. In support of this hypothesis, it has been reported that amphibians can adjust the intensity of their antipredator response to match the degree of threat posed by varying alarm cue concentrations (Petranka 1989;Rohr & Madison 2001;Mirza et al 2006). Other similar studies in the common frog found inconsistent evidences that the presence of chemical cues from tadpole predators might delay hatching (Laurila et al 2001(Laurila et al , 2002Van Buskirk 2002).…”

“…Mathis et al 1993;Hickman et al 2004;Ferrari Vol. 17, 2007 Embryonic exposure to conspecific cues 171 et al 2005;Mirza et al 2006;Mandrillon & Saglio 2007), without any sign of cue deterioration. Each sub-sample was equivalent to six crushed conspecifics, either embryos or tadpoles.…”