Abstracts (first author)
Chemical anthropogenic pollution interferes in prey recognition systems
Chemical detection of predator cues is crucial for aquatic prey, because it allows predator avoidance and activation of plastic antipredatory defenses. This is the case of many larval amphibians that respond to water-borne cues from potential predators by strongly reducing activity levels. However, as a consequence of increasing anthropogenic activity, a variety of harmful contaminants are dumped in freshwater ecosystems, where they can create interferences in the cue recognition system of tadpoles. Here we analyze the potential effects of two contaminants (i. e., 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 swimming activity of tadpoles in presence and absence of water-borne chemical cues from dragonflies, at different concentrations of humic acid and ammonium nitrate. Changes in tadpole activity associated to toxicity were non-significant. In contrast, the interaction between predator cues and presence of contaminants was significant: tadpoles effectively responded to predator cues in the absence of pollutants by reducing their swimming activity, but remained unresponsive to predator cues when either humic acid or ammonium nitrate were added, even at low concentrations. These interferences due to chemical anthropogenic pollution may pose a threat to the cue recognition systems of prey-predator interactions evolved in amphibian populations.
Learned predator recognition allows activation of defensive behaviour and enhances survival against alien predators
Alien predators are one of the major causes of rapid decline and extinction of native species, because they often create novel ecological contexts in which the antipredatory responses of native organisms are no longer adaptive. The red swamp crayfish, Procambarus clarkii, is a harmful invasive species in aquatic systems worldwide that is causing great ecological impact on native amphibian populations through intense predation of eggs and tadpoles. Larval amphibians are often capable of innately responding to the presence of chemical cues from local predators through changes in morphology and behaviour. Nonetheless, naïve tadpoles are often incapable of recognising alien predators with whom they have no shared evolutionary history. For this reason, amphibian species are especially vulnerable to the introduction of new predators. However, given enough time, native populations might acquire, by means of rapid adaptation or the evolution of phenotypic plasticity, the ability to escape from alien predators. Here we show that naïve tadpoles of the western spadefoot toad, Pelobates cultripes, cannot innately recognise water-borne cues from P. clarkii. Nevertheless, we also show that P. cultripes tadpoles can learn to recognise the cues of this alien predator as a threat when they are exposed to predator cues combined with conspecific alarm cues. Furthermore, we show that tadpoles that learned to recognise the new predator experienced higher survival during staged predation trials with invasive crayfish. This cognitive ability of tadpoles might be critical for amphibian populations to trigger inducible defences against alien predators, thus tempering the immediate impact of invasions through behavioural plasticity and persist long enough for genetic variants to appear and respond to selection.