The metabolic pace-of-life syndrome of Xyrichtys novacula Linnaeus, 1758

Abstract

[eng] The exploitation of wild-living animals by humans is never random with respect to the traits carried by the individual. Induced adaptive changes observed over time in exploited populations are due likely to selection against desirable phenotypes, a process called “unnatural” selection. Phenotypic variation in key life-history traits represent thus an important determinant for population dynamics and strategies in fish. Recently, individual variation in the tempo of life histories has been linked to wider patterns of phenotypic covariance commonly observed in an applied range of physiological, morphological, and behavioural traits, a phenomenon that has been termed "pace-of-life syndrome" (POLS). In this study, we aimed to investigate the correlation between metabolism, behaviour, and growth measured under laboratory conditions of the teleost fish species Xyrichtys novacula to detect pace-of-life syndromes. For this purpose, firstly we developed a new methodology to estimate basal metabolic rate (RMR) using an intermittent-flow respirometry system. For behaviour we focused this work on individual patterns of activity/rest behaviours using circadian-related quantitative metrics measured through a recently established high-throughput tracking system based on deep-learning for behavioural annotation. And for life-history, individual annual growth rates were analysed by examining the marks contained in the otoliths. The experiments were conducted in two twoweek batches at the Marine Research and Aquaculture Laboratory (LIMIA) located in Andratx (Mallorca, Spain). The individuals were kept isolated under constant temperature and a 12 h light/ 12 h dark photoperiod (simulating natural environmental conditions). The results demonstrated that individuals with less fragmented biological rhythms experience faster growth compared to those with more fragmented rhythms (higher intraday variability). Growth rate was independent of resting metabolic rate, and individuals with greater synchronization with the photoperiod (higher interdaily stability) and lower maximum activity (amplitude) have a higher resting metabolic rate. These findings are relevant and provide support for the theoretical framework of POLS in our case study. This study demonstrates the utility of the new methodology for estimating oxygen consumption and represents the first attempt to investigate the correlation between metabolism, behaviour, and growth in this species under laboratory conditions. However, the factors causing variations in the pace-of-life among populations and individuals are still unknown in most species, necessitating further studies.