Divergent responses of exposed and naive Pacific tree frog tadpoles to invasive predatory crayfish

Raised by aliens: constant exposure to an invasive predator triggers morphological but not behavioural plasticity in a threatened species tadpoles

During biotic invasions, native communities are abruptly exposed to novel and often severe selective pressures. The lack of common evolutionary history with invasive predators can hamper the expression of effective anti-predator responses in native prey, potentially accelerating population declines. Nonetheless, rapid adaptation and phenotypic plasticity may allow native species to cope with the new ecological pressures. We tested the hypothesis that phenotypic plasticity is fostered when facing invasive species and evaluated whether plasticity offers a pool of variability that might help the fixation of adaptive phenotypes. We assessed behavioural and morphological trait variation in tadpoles of the Italian agile frog (Rana latastei) in response to the invasive crayfish predator, Procambarus clarkii, by rearing tadpoles under different predation-risk regimes: non-lethal crayfish presence and crayfish absence. After two-month rearing, crayfish-exposed tadpoles showed a plastic shift in their body shape and increased tail muscle size, while behavioural tests showed no effect of crayfish exposure on tadpole behaviour. Furthermore, multivariate analyses revealed weak divergence in morphology between invaded and uninvaded populations, while plasticity levels were similar between invaded and uninvaded populations. Even if tadpoles displayed multiple plastic responses to the novel predator, none of these shifts underwent fixation after crayfish arrival (10–15 years). Overall, these findings highlight that native prey can finely tune their responses to invasive predators through plasticity, but the adaptive value of these responses in whitstanding the novel selective pressures, and the long-term consequences they can entail remain to be ascertained.

Overcoming prey naiveté: Free-living marsupials develop recognition and effective behavioral responses to alien predators in Australia

Naiveté in prey arises from novel ecological mismatches in cue recognition systems and antipredator responses following the arrival of alien predators. The multilevel naiveté framework suggests that animals can progress through levels of naiveté toward predator awareness. Alternatively, native prey may be preadapted to recognize novel predators via common constituents in predator odors or familiar predator archetypes. We tested predictions of these competing hypotheses on the mechanisms driving behavioral responses of native species to alien predators by measuring responses of native free-living northern brown bandicoots (Isoodon macrourus) to alien red fox (Vulpes vulpes) odor. We compared multiple bandicoot populations either sympatric or allopatric with foxes. Bandicoots sympatric with foxes showed recognition and appropriate antipredator behavior toward fox odor via avoidance. On the few occasions bandicoots did visit, their vigilance significantly increased, and their foraging decreased. In contrast, bandicoots allopatric with foxes showed no recognition of this predator cue. Our results suggest that vulnerable Australian mammals were likely naïve to foxes when they first arrived, which explains why so many native mammals declined soon after fox arrival. Our results also suggest such naiveté can be overcome within a relatively short time frame, driven by experience with predators, thus supporting the multilevel naiveté framework.

Developmental thermal plasticity of prey modifies the impact of predation

Environmental conditions during embryonic development can influence the mean expression of phenotypes as well as phenotypic responses to environmental change later in life. The resulting phenotypes may be better matched to their environment and more resilient to environmental change, including human induced climate change. However, whether plasticity does improve success in an ecological contexts is unresolved. In a microcosm experiment, we show that developmental plasticity in embryos of the frog Limnodynastes peronii is beneficial by increasing survivorship of tadpoles in the presence of predators when egg incubation (15°C or 25°C) and tadpole acclimation temperatures in microcosms (15°C or 25°C) coincided at 15°C. Tadpoles that survived predation were smaller, and had faster burst swimming speeds than those kept in no-predator controls, but only at high (25°C) egg incubation or subsequent microcosm temperatures. Metabolic rates were determined by a three-way interaction between incubation and microcosm temperatures, and predation; maximal glycolytic and mitochondrial metabolic capacities (enzyme activities) were lower in survivors from predation compared to controls, particularly when eggs were incubated at 25°C. We show that thermal conditions experienced during early development are ecologically relevant by modulating survivorship from predation. Importantly, developmental thermal plasticity also impacts population phenotypes indirectly by modifying species interactions and the selection pressure imposed by predation.