Summary
1.Inter-individual variation in metabolic rate exists in a wide range of taxa. While this variation appears to be linked to numerous aspects of animal behaviour and personality, the ecological relevance of these relationships is not understood. The behavioural response of individual fish to acute aquatic hypoxia, for example, could be related to metabolic rate via influences on oxygen demand or the willingness to take risks. Individuals with higher metabolic rates could show greater hypoxia-associated increases in activity that could allow them to locate areas with increased oxygen availability but that also make them susceptible to predation. Any relationship between metabolic rate and risk-taking behaviour among individual fish could therefore be modulated by environmental oxygen levels, perhaps becoming stronger as oxygen availability declines. 2. We measured spontaneous swimming activity as an index of risk-taking by juvenile European sea bass in normoxia, moderate hypoxia (40% air saturation) and severe hypoxia (20% air saturation) after being startled by a predator model. All fish were also separately measured for routine metabolic rate by measuring oxygen uptake. 3. In hypoxia, fish re-emerged from cover sooner after a simulated attack and were generally more active than when the same fish were startled in normoxia. In addition, individual activity and risk-taking in severe hypoxia were positively correlated with metabolic rate. Aquatic surface respiration was a major contributor towards increased activity in hypoxia and was positively related to metabolic rate during severe hypoxia. There were no relationships between risk-taking and metabolic rate in moderate hypoxia or normoxia. 4. Relative measures of risk-taking among individual fish were not consistent among oxygen levels, further suggesting that individuals differ in sensitivity to hypoxia and the degree to which this environmental stressor affects risk-taking behaviour. 5. These results suggest that fish with relatively high metabolic rates become more active during acute hypoxia, possibly leading to increased susceptibility to predation in response to differences in metabolic demand. In addition, the relationship between metabolic rate and risk-taking may only be observable during exposure to a physiological stressor or such a stressor may strengthen any relationships observable under more benign conditions.
Researchers and others involved with the Zoonoses and Emerging Livestock Systems (ZELS) initiative gathered in Tanzania earlier this year to discuss progress with projects being carried out as part of the five‐ year programme. Mary Ryan and Sarah Cleaveland report
Improvements in genetic and genomic technology have enabled field-deployable molecular laboratories and these have been deployed in a variety of epidemics that capture headlines. In this editorial, we highlight the importance of building physical and personnel capacity in low and middle income countries to deploy these technologies to improve diagnostics, understand transmission dynamics and provide feedback to endemic communities on actionable timelines. We describe our experiences with molecular field research on schistosomiasis, trypanosomiasis and rabies and urge the wider tropical medicine community to embrace these methods and help build capacity to benefit communities affected by endemic infectious diseases.
In freshwater environments, chemosensory cues play an important role in predator-prey interactions. Prey use a variety of chemosensory cues to detect and avoid predators. However, whether predators use the chemical cues released by disturbed or stressed prey has received less attention. Here we tested the hypothesis that the disturbance cue cortisol, in conjunction with visual cues of prey, elevates predatory behavior. We presented predators (perch, Perca fluviatilis) with three chemosensory choice tests and recorded their location, orientation, and aggressive behavior. We compared the responses of predators when provided with (i) visual cues of prey only (two adjacent tanks containing sticklebacks); (ii) visual and natural chemical cues of prey vs. visual cues only; and (iii) visual cues of prey with cortisol vs. visual cues only. Perch spent a significantly higher proportion of time in proximity to prey, and orientated toward prey more, when presented with a cortisol stimulus plus visual cues, relative to presentations of visual and natural chemical cues of prey, or visual cues of prey only. There was a trend that perch directed a higher proportion of predatory behaviors (number of lunges) toward sticklebacks when presented with a cortisol stimulus plus visual cues, relative to the other chemosensory conditions. But they did not show a significant increase in total predatory behavior in response to cortisol. Therefore, it is not clear whether water-borne cortisol, in conjunction with visual cues of prey, affects predatory behavior. Our results provide evidence that cortisol could be a source of public information about prey state and/or disturbance, but further work is required to confirm this.
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