Search

Studies on the impacts of variation of biotic interactions at key life cycle stages are crucial to understand the interface between ecological and developmental processes. Predators exert a major impact on prey fitness. Although direct consumption entails the greatest effect, predators can affect prey by means of other mechanisms. For instance, injuries inflicted by failed predation attempts can jeopardize prey fitness, even beyond the short-term. In anuran tadpoles, failed predation typically results in partial tail loss, which is known to reduce swimming speed. However, the potential consequences of tadpole partial tail loss after metamorphosis remain understudied. Because tail materials could be important in conforming metamorph body, we assess the effects of tadpole partial tail loss on metamorph body size in Iberian spadefoot toads Pelobates cultripes. We clipped 55% tail length of pre-tail-resorption stage anesthetized tadpoles, and compared their body size as metamorphs with anesthetized and non-anesthetized non-tail-clipped controls. Also, we tested whether tail length correlated with metamorph body size of individuals of the control groups. Tail-clipped tadpoles produced smaller metamorphs than both controls (the bdy size of metamorphs from both controls was similar), which could incur costs in mid-term survival or time to first reproduction. This effect could be particularly important in areas with introduced predators, if autochthonous tadpoles lack defenses against them. Results suggest that materials resorbed from tadpole tail tissues might be reallocated into metamorph body, according to the negative effect of shorter tails in a correlational analysis, and clipped tails in an experimental test, on metamorph body size.

As an evolutionary force, predation increases predator fitness, whereas prey future fitness is reduced to zero. Mesopredators are subjected to pressures as both predator and prey, which could generate trade-offs between predatory and anti-predatory behaviours. We subjected larvae of the mesopredator Pleurodeles waltl newt to a potential conflict of interest between reducing predation risk and fulfilling nutritional requirements. For this, we performed an experiment with a factorial design: (1) to induce different urges as predators, individuals underwent either restricted or unrestricted feeding; and (2) to induce different urges as prey, individuals were exposed to environments with and without predator snake kairomones. We recorded activity rate, swim rate, flight initiation distance (FID) and escape speed. FID increased in the presence of kairomones, as predicted by escape theory when the costs of not fleeing are greater than those of fleeing. Escape speed increased in the presence of kairomones, but only in restricted feeding larvae, probably due to lower body weight because of reduced food intake. We detected no effect of treatment on activity or swim rates. Predation risk apparently outweighed the costs of feeding opportunities lost rather than generated a behavioural trade-off. Collectively, the data suggested a greater effect of predator avoidance than of prey acquisition.