Consistent behavioural variation in Asellus aquaticus does not correlate with individual metabolism.

Abstract Consistent individual differences in behaviour are common across animal taxa and often form correlated suites of traits known as behavioural syndromes. These syndromes may be shaped by underlying physiological mechanisms, including metabolic rate, as proposed by the pace-of-life syndrome (POLS) hypothesis. POLS suggests that behaviour, metabolism, and life-history traits evolve as integrated responses to ecological pressures. Here we investigated the relationship between consistent individual behavioural variation and metabolic rate in the freshwater isopod Asellus aquaticus. We hypothesized that individual behavioural traits; exploration, activity, and escape behaviour, were repeatable and formed a behavioural syndrome, and that these traits correlated with routine metabolic rate, following POLS hypothesis. Using a mixed model approach, we measured the repeatability of these behaviours and metabolic rates in field-collected Asellus individuals over an 18-days experimental period. Repeatability (r) of behavioural traits ranged from 0.31 to 0.52, and we observed positive correlations (correlation coefficients 0.50 – 0.92) between exploration, activity, and escape behaviour, indicating the presence of a behavioural syndrome. The repeatability of metabolic rate was high (r = 0.70), but contrary to our hypothesis, no correlation was found between metabolic rate and any of the measured behaviours. These findings suggest that while Asellus aquaticus exhibits consistent individual variation in both behaviour and metabolic rate, the predicted link between behaviour and metabolic rate did not hold. Further studies on invertebrate taxa, underrepresented in the literature, may help explain conflicting observations of links between behaviour and metabolism, and to identify the underlying mechanisms that drive these patterns.