Small within-day increases in temperature affects boldness and alters personality in coral reef fish

Abstract

Consistent individual differences in behaviour, termed personality, are common in animal populations and can constrain their responses to ecological and environmental variation, such as temperature. Here, we show for the first time that normal within-daytime fluctuations in temperature of less than 3 degrees C have large effects on personality for two species of juvenile coral reef fish in both observational and manipulative experiments. On average, individual scores on three personality traits (PTs), activity, boldness and aggressiveness, increased from 2.5- to sixfold as a function of temperature. However, whereas most individuals became more active, aggressive and bold across temperature contexts (were plastic), others did not; this changed the individual rank order across temperatures and thus altered personality. In addition, correlations between PTs were consistent across temperature contexts, e.g. fish that were active at a given temperature also tended to be both bold and aggressive. These results (i) highlight the importance of very carefully controlling for temperature when studying behavioural variation among and within individuals and (ii) suggest that individual differences in energy metabolism may contribute to animal personality, given that temperature has large direct effects on metabolic rates in ectotherms.

Figure 1.

(a) Predicted activity, (b) aggressiveness and (c) boldness (latency to emerge from shelter after threat) trajectories for individual yellow damselfish across temperature contexts obtained from an experiment where within-day temperature varied. Shown are the back-transformed response functions for all 32 individuals from a mixed-model analyses of behavioural consistency, reflecting the temperature range across which data were collected for each PT. Note that shorter latencies to emerge following predatory threat indicate greater boldness, and that this PT was not transformed for analysis. Interindividual differences in the slopes for aggressiveness and latency as a function of temperature were not statistically significant, so estimates of individual slopes for these behaviours are not included in this figure.

Figure 2.

Predicted activity and boldness (latency to emerge from shelter after threat) trajectories for 29 individual P. bankanensis damselfish across temperature contexts, obtained from an experiment where temperature was directly manipulated. Shown are the (a) back-transformed and (b) raw data response functions for all 29 individuals, reflecting the temperature range across which data were collected for each PT. Note that shorter latencies to emerge following predatory threat indicate greater boldness.