Abstract
SynopsisGroup 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.
Highlights
An animal social group is any set of socially interacting individuals that remain together in space and time (Krause and Ruxton 2002)
We investigated whether exposure to a given group size and shelter availability could influence metabolic rates of Eurasian minnow Phoxinus phoxinus, a small Cyprinid naturally living in social groups (Magurran 1986)
The main goal of this study was to assess whether being in a smaller or larger group of conspecifics and having plant shelter available or not could modulate expression of metabolic traits. Both before and after fish were exposed to different social treatments, minimum metabolic rates estimated in presence of shelter were lower than those estimated in absence of shelter
Summary
An animal social group is any set of socially interacting individuals that remain together in space and time (Krause and Ruxton 2002). There is some evidence that the recent social environment can affect behavioral responses in later contexts, even when individuals are alone (Jolles et al 2016). This suggests that the social environment could modulate an individual’s behavioral expression or capacity, yet the ways in which the phenotype of individual animals interacts with their social environment remain largely unknown, including how social dynamics affect individual physiological traits
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