Is repeatability of metabolic rate influenced by social separation? A test with a teleost fish

The Potential for Physiological Performance Curves to Shape Environmental Effects on Social Behavior

As individual animals are exposed to varying environmental conditions, phenotypic plasticity will occur in a vast array of physiological traits. For example, shifts in factors such as temperature and oxygen availability can affect the energy demand, cardiovascular system, and neuromuscular function of animals that in turn impact individual behavior. Here, we argue that nonlinear changes in the physiological traits and performance of animals across environmental gradients—known as physiological performance curves—may have wide-ranging effects on the behavior of individual social group members and the functioning of animal social groups as a whole. Previous work has demonstrated how variation between individuals can have profound implications for socially living animals, as well as how environmental conditions affect social behavior. However, the importance of variation between individuals in how they respond to changing environmental conditions has so far been largely overlooked in the context of animal social behavior. First, we consider the broad effects that individual variation in performance curves may have on the behavior of socially living animals, including: (1) changes in the rank order of performance capacity among group mates across environments; (2) environment-dependent changes in the amount of among- and within-individual variation, and (3) differences among group members in terms of the environmental optima, the critical environmental limits, and the peak capacity and breadth of performance. We then consider the ecological implications of these effects for a range of socially mediated phenomena, including within-group conflict, within- and among group assortment, collective movement, social foraging, predator-prey interactions and disease and parasite transfer. We end by outlining the type of empirical work required to test the implications for physiological performance curves in social behavior.

Social Group Size and Shelter Availability Influence Individual Metabolic Traits in a Social Fish

Group living is widespread among animal species and yields both costs and benefits. Presence of conspecifics can restrict or enhance the expression of individual behavior, and the recent social environment is thought to affect behavioral responses in later contexts, even when individuals are alone. However, little is known about how social group size influences the expression of individual physiological traits, including metabolic rates. There is some evidence that shoaling can reduce fish metabolic rates but this variable may be affected by habitat conditions such as shelter availability via density-dependent processes. We investigated how social group size and shelter availability influence Eurasian minnow (Phoxinus phoxinus) metabolic rates estimated by respirometry. Respirometry trials were conducted on fish in isolation before and after they were housed for 3 weeks in a social treatment consisting in a specific group size (n = 4 or 8) and shelter availability (presence or absence of plant shelter in the experimental tank). Plant shelter was placed over respirometers for half of the duration of the respirometry trials, allowing estimation of minimum daytime and nighttime metabolic rates in both conditions (in the presence or absence of plant shelter). Standard metabolic rate (SMR), maximum metabolic rate (MMR), and aerobic scope were also estimated over the entire trial. Minimum daytime and nighttime metabolic rates estimated while in presence of plant shelter were lower than when estimated in absence of plant shelter, both before and after individuals were housed in their social treatment. After the social treatment, SMRs were higher for fish that were held in groups of 4 as compared with those of fish held in groups of 8, while MMR showed no difference. Plant shelter availability during the social treatments did not influence SMR or MMR. Our results suggest that social group size may directly influence energy demands of individuals, highlighting the importance of understanding the role of group size on variations in physiological traits associated with energy expenditure.

Acute warming in winter eliminates chemical alarm responses in threatened Qinling lenok Brachymystax lenok tsinlingensis

Knowledge of how temperature influences animal behavior is critical to understanding and predicting impacts of changing climate on individual species and biotic interactions. However, the effects of climate change, especially winter warming in freshwater systems, on fish behaviors and the use of chemical information have been largely unexplored. Qinling lenok Brachymystax lenok tsinlingensis, an endangered salmonid species endemic to the Qinling Mountain Range, China, is currently experiencing population decline and is a potential biological indicator of warming winter climate effects on freshwater fishes due to its temperature sensitivity and required habitat of small, cold-water streams. Our objective was to determine if transient winter warming (increases of ~4 °C) consistent with seasonal maxima in line with near-future climate projections will affect antipredator responses to damage-released chemical alarm cues in B. lenok tsinlingensis. Wild fish were collected during winter and held in captivity under food deprivation for four days, during which half were acclimated to a warmer temperature (6 °C) while the other half were maintained at ambient levels (2 °C). Individual acclimated fish were then exposed to injections of either conspecific alarm cues to simulate elevated predation risk or stream water as a control treatment. Focal fish demonstrated responses consistent with antipredator behaviors to alarm cues at ambient temperature, but no significant behavioral responses to alarm cues were found relative to controls at the warmer temperature. These results support our hypothesis that winter warming will negatively influence antipredator responses and indicate that projected warmer temperature patterns in winter may have significant impacts on chemically mediated predator-prey interactions in cold-water streams.