Telomere length covaries with personality in wild brown trout

- Telomeres likely play a crucial role in regulating organismal senescence and intrinsic lifespan.
- The role of telomeres in regulating state-dependent personality variation is currently overlooked.
- Wild juvenile brown trout (Salmo trutta) with shorter fin telomeres behaved consistently more boldly and aggressively.
- We suggest telomere dynamics are important in integrating personality traits with other state variables.

The prevalence of consistent among-individual differences in behaviour, or personality, makes adaptive sense if individuals differ in stable state variables that shift the balance between the costs and benefits of their behavioural decisions. These differences may give rise to both individual differences in, and covariance among, behaviours that influence an individual's exposure to risks. We here study the link between behaviour and a candidate state variable previously overlooked in the study of state-dependent personality variation: telomere length. Telomeres are the protective endcaps of chromosomes and their erosion with age is thought to play a crucial role in regulating organismal senescence and intrinsic lifespan. Following evidence that shorter telomeres may reduce the lifespan of animals in a wide range of taxa, we predict individuals with shorter telomeres to behave more boldly and aggressively. In order to test this, we measured telomere length and behaviour in wild juvenile brown trout (Salmo trutta). We found individuals with shorter fin telomeres to behave consistently more boldly and aggressively under controlled conditions in the laboratory. No such relationship was found with muscle telomere length 3-4 months after the behavioural assays. We suggest that telomere dynamics are an important factor integrating personality traits with other state variables thought to be important in the regulation of behaviour, such as metabolism, disease resistance and growth.