Effects of the invasive Tilapia on the Common Spiny Loach (Cypriniformes: Cobitidae: Lepidocephalichthys thermalis) - implications for conservation

The introduction of invasive species leading to decline of freshwater fauna is a major concern for conservation biologists. In this study we examined the effect of introduced Tilapia on the survival of the loach Lepidocephalichthys thermalis via predation experiments with Tilapia and a native predator, the Snakehead fish Channa gachua. Examining the chemoecology of prey-predator interactions, we found that L. thermalis failed to detect water-borne cues from Tilapia but did recognize cues from C. gachua, indicating innate predator recognition. We also observed that L. thermalis can learn to associate kairomones with Tilapia when conditioned with kairomones and injured conspecific cues. Trained L. thermalis showed higher survival during Tilapia predation trials. Thus under experimental conditions the vulnerability of L. thermalis to Tilapia predation due to failure to detect chemical cues can be reduced via associative training. It remains to be determined how useful this behavioral plasticity can be in wild L. thermalis populations exposed to introduced Tilapia.

Metamorphosing reef fishes avoid predator scent when choosing a home

Most organisms possess anti-predator adaptations to reduce their risk of being consumed, but little is known of the adaptations prey employ during vulnerable life-history transitions when predation pressures can be extreme. We demonstrate the use of a transition-specific anti-predator adaptation by coral reef fishes as they metamorphose from pelagic larvae to benthic juveniles, when over half are consumed within 48 h. Our field experiment shows that naturally settling damselfish use olfactory, and most likely innate, predator recognition to avoid settling to habitat patches manipulated to emit predator odour. Settlement to patches emitting predator odour was on average 24–43% less than to control patches. Evidence strongly suggests that this avoidance of sedentary and patchily distributed predators by nocturnal settlers will gain them a survival advantage, but also lead to non-lethal predator effects: the costs of exhibiting anti-predator adaptations. Transition-specific anti-predator adaptations, such as demonstrated here, may be widespread among organisms with complex life cycles and play an important role in prey population dynamics.

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

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.

Innate predator recognition in newly-hatched Atlantic salmon

It is well established that fish can learn to associate odours from potential predators with risk and alter their behaviour accordingly. However, newly-hatched individuals have few opportunities for acquired predator recognition and may depend on unlearnt (innate) responses. We therefore considered whether newly hatched Atlantic salmon fry (alevins) exhibit innate predator recognition and whether this recognition could be improved by prior exposure to combined conspecific and predator (pike) odours. Our investigation showed that the response to pike odour was not affected by previous exposure to pike odour and conspecific tissue extract but was consistent with innate recognition of pike as predators. Trials conducted using odour from a non-piscivorous species confirmed that the fish were not simply reacting to a novel stimulus.