Individual differences in personality and cognition in bank voles (Myodes glareolus)

Consistent among-individual differences are found in most areas of biological research, and appear to constrain animals’ plasticity and thus the possibility to adapt optimally to the environment. Recent years have seen increased interest in individual variation in behaviour, cognition and physiology, the proximate causes and the evolutionary mechanisms maintaining this variation. Not only there is reason to believe that individual differences in these domains affect fitness, it is likely that they are inter-related, forming a complex net of interactions regulated by different trade-offs. Empirical testing of recent theoretical framework ─ suggesting possible mechanisms linking behaviour, cognition and physiology ─ provided mixed findings. The aim of this thesis was to investigate whether individual differences in behaviour (animal personality), cognition and physiology are linked, and whether individuals that present different profiles display ecologically-relevant differences that might affect their fitness. To achieve this goal I assessed 86 bank voles (Myodes glareolus) for personality (i.e. activity and boldness), associative learning and reversal learning, as well as foraging and anti-predator strategies. I also evaluated their response to challenges, through measurement of faecal corticosterone metabolites. Main results support the predictions made by authors Carere and Locurto (2011) and Sih and Del Giudice (2012). Voles’ personality and cognitive style were indeed connected, and constrained by a speed-flexibility/accuracy trade-off. Proactive (i.e. bolder and more active) individuals were faster but more rigid learners, whereas reactive individuals (i.e. shyer and less active) proved slower but more flexible. Personality and cognitive style predicted the individual bias in a risk-reward trade-off. Proactive individuals tended to maximise reward at the cost of running higher risks, and reactive individuals favoured safety in spite of increased searching effort. However, body weight changes did not differ between the two groups. The response to a moderate challenge was not correlated with either personality or cognitive style. However, individual profiles predicted individual endocrine state in two relatively undisturbed conditions. Taken together, these result show consistent individual differences in personality, cognition and physiology. Such differences appear inter-related and extend to fitness-relevant traits. These results might help future research in the investigation of the evolutionary maintenance of among-individual variation.