The fast and the curious II: performance, personality, and metabolism in Karoo bush rats

Abstract

Personality traits (e.g. activity, exploration, boldness) are frequently correlated with each other and with various other traits of biological importance. According to the performance, allocation, and independent models of energy management, the relationship between personality traits and resting metabolic rate (RMR) is predicted to be either positive, negative, or nil. As for the relationship between personality traits and locomotor performance, the trait compensation and co-specialisation hypotheses respectively predict a positive and negative relationship. To test for associations between personality, metabolism, and performance, we studied a wild population of Karoo bush rat (Myotomys unisulcatus) in South Africa. During summer 2018, we captured 45 individuals (38 females and 7 males) a total of 293 times and repeatedly measured docility (time spent immobile during a bag test), exploration (distance moved in an open-field test), sprint speed, and RMR. We found a behavioural syndrome in our population, as more docile individuals covered less distance in the exploration test (r ± SE = − 0.74 ± 0.21). RMR was not correlated with any trait; therefore, the independent energy management model applies to this population. Fast sprinters were less explorative in the novel environment than slow sprinters (r ± SE = − 0.41 ± 0.21), going against the prediction of the phenotypic compensation hypothesis and suggesting co-specialisation of these traits. A similar result was previously observed in two other rodent species, suggesting that exploratory behaviour and locomotor performance may interact in an additive instead of compensatory way. Given the apparent complexity of the links between performance, behaviour, and metabolism, more studies are needed in order to understand their relationships. In this study, we test alternative energy management models and hypotheses predicting different relationships between behavioural, performance, and metabolic traits. Our results support the independent model of energy management, since resting metabolic rate was not correlated with either docility or exploration. The negative relationship between exploration and sprint speed is counter to the intuitive idea that more explorative individuals should be better equipped to deal with the increased risks of predation, but instead supports the co-specialisation hypothesis. Finally, we emphasise the importance of partitioning the variance in raw measurements as a way to better appreciate the variability in measurements of metabolic rate and locomotor performance. Such multilevel analyses provide an idea of the relative variability at among-individual level vs. other levels (tests, trials, and residuals), which might have important implications for the understanding of how factors like stress and motivation might potentially generate or obfuscate relationships between behavioural, performance, and metabolic traits.