Effects of dispersant-treated oil upon behavioural and metabolic parameters of the anti-predator response in juvenile European sea bass (Dicentrarchus labrax)

Acute exposure to oil and oil dispersants can cause a wide range of physiological dysfunctions in marine fish species and evidences for consequences on behaviour are also increasing. In response to the presence of predators or to food availability, the modulation of locomotor activity and schools' behaviour enable fish to maximize their survival rates. However, the degree to which this regulatory process is affected by exposure to oil and/or dispersants is yet unknown. Here we investigated the effect of a 62-h experimental exposure to dispersant-treated oil on the behavioural (shoal cohesion, spontaneous activity) and metabolic (oxygen consumption) responses to simulated predation in juvenile European sea bass, Dicentrarchus labrax L. Our results suggest that exposure to petroleum hydrocarbons may affect negatively individual fitness through impaired ability to respond to predation. Shoal cohesion was not affected, but fish swimming activity was higher than control individuals under predation pressure and the amplitude of their metabolic response was significantly reduced. Fish recovered from alteration of their metabolic response 7 days post-exposure. Additionally, a strong habituation component was observed in C fish and the absence of such pattern in E fish suggest altered capacity to habituate over time to the surrounding environment and possible impairments of the related cognitive performances. Altogether, our data show that juvenile sea bass exposed to oil exhibit transient physiological dysfunctions and impairments of complex behaviours that may have major population-level consequences.

Larval habitat selection by females of two malaria vectors in response to predation risk

For species lacking parental care, selection of a suitable habitat for their offspring, with a limited predation risk, is important. The ability of two African malaria mosquito females to detect a predation threat for their larvae was assessed through an oviposition choice test design. Our results suggest that gravid females of both Anopheles gambiae s.s. and An. coluzzii (Diptera, Culicidae) were able to detect the presence of a predator (Anisops jaczewskii, Notonectidae, Hemiptera; backswimmer). However, An. coluzzii were more likely to choose the cups containing predation cues while An. gambiae tended to avoid them for oviposition. Anopheles coluzzii females might use either alarm cues or pre-digestive cues from the external prey digestion to gauge the threat level, while An. gambiae females might use predator cues (odor or vibrations) or digestive cues from the predator. Compared to An. gambiae, An. coluzzii females seemed to accept the predation threat for their larvae to some extent. These results are consistent with the observed larval distribution in the field. Anopheles coluzzii larvae are found in complex permanent reservoirs in which the predation pressure is high, while An. gambiae larvae are more frequently found in temporary reservoirs with a lower predation threat. To our knowledge, this is the first time such a divergence in oviposition strategies regarding predation risk management by females is shown between closely related mosquito species.

Response of Bolivian gray titi monkeys (Plecturocebus donacophilus) to an anthropogenic noise gradient: behavioral and hormonal correlates

Worldwide urban expansion and deforestation have caused a rapid decline of non-human primates in recent decades. Yet, little is known to what extent these animals can tolerate anthropogenic noise arising from roadway traffic and human presence in their habitat. We studied six family groups of titis residing at increasing distances from a busy highway, in a park promoting ecotourism near Santa Cruz de la Sierra, Bolivia. We mapped group movements, sampled the titis’ behavior, collected fecal samples from each study group and conducted experiments in which we used a mannequin simulating a human intrusion in their home range. We hypothesized that groups of titi monkeys exposed to higher levels of anthropogenic noise and human presence would react weakly to the mannequin and show higher concentrations of fecal cortisol compared with groups in least perturbed areas. Sound pressure measurements and systematic monitoring of soundscape inside the titis’ home ranges confirmed the presence of a noise gradient, best characterized by the root-mean-square (RMS) and median amplitude (M) acoustic indices; importantly, both anthropogenic noise and human presence co-varied. Study groups resided in small, overlapping home ranges and they spent most of their time resting and preferentially used the lower forest stratum for traveling and the higher levels for foraging. Focal sampling analysis revealed that the time spent moving by adult pairs was inversely correlated with noise, the behavioral change occurring within a gradient of minimum sound pressures ranging from 44 dB(A) to 52 dB(A). Validated enzyme-immunoassays of fecal samples however detected surprisingly low cortisol concentrations, unrelated to the changes observed in the RMS and M indices. Finally, titis’ response to the mannequin varied according to our expectation, with alarm calling being greater in distant groups relative to highway. Our study thus indicates reduced alarm calling through habituation to human presence and suggests a titis’ resilience to anthropogenic noise with little evidence of physiological stress.

Proportional fitness loss and the timing of defensive investment: a cohesive framework across animals and plants

The risk of consumption is a pervasive aspect of ecology and recent work has focused on synthesis of consumer-resource interactions (e.g., enemy-victim ecology). Despite this, theories pertaining to the timing and magnitude of defenses in animals and plants have largely developed independently. However, both animals and plants share the common dilemma of uncertainty of attack, can gather information from the environment to predict future attacks and alter their defensive investment accordingly. Here, we present a novel, unifying framework based on the way an organism's ability to defend itself during an attack can shape their pre-attack investment in defense. This framework provides a useful perspective on the nature of information use and variation in defensive investment across the sequence of attack-related events, both within and among species. It predicts that organisms with greater proportional fitness loss if attacked will gather and respond to risk information earlier in the attack sequence, while those that have lower proportional fitness loss may wait until attack is underway. This framework offers a common platform to compare and discuss consumer effects and provides novel insights into the way risk information can propagate through populations, communities, and ecosystems.

Does corticosterone mediate predator-induced responses of larval Hylarana indica?

Prey-predator interactions have been studied extensively in terms of morphological and behavioural responses of prey to predation risk using diverse model systems. However, the underlying physiological changes associated with morphological, behavioural or life historical responses have been rarely investigated. Herein, we studied the effect of chronic predation risk on larval growth and metamorphosis of Hylarana indica and the underlying physiological changes in prey tadpoles. In the first experiment, tadpoles were exposed to a caged predator from Gosner stage 25-42 to record growth and metamorphosis. Further, whole body corticosterone (CORT) was measured to determine the physiological changes underlying morphological and life historical responses of these prey tadpoles. Surprisingly, tadpoles experiencing continuous predation risk grew and developed faster and metamorphosed at a larger size. Interestingly, these tadpoles had significantly lower CORT levels. In the second experiment, tadpoles were exposed to predation risk (PR) or PR+CORT from stage 25-42 to determine the role of CORT in mediating predator-induced responses of H. indica. Tadpoles facing continuous predation risk grew and developed faster and metamorphosed at a larger size reinforcing the results of the first experiment. However, when CORT was administered along with predation risk, tadpoles grew and developed slowly leading to delayed metamorphosis. Interestingly, growth and metamorphic traits of tadpoles exposed to PR+CORT were comparable to those of the control group indicating that exogenous CORT nullified the positive effect of predation risk. Apparently, CORT mediates predator-induced morphological responses of H. indica tadpoles by regulating their physiology.