Abstract
Animal personality traits are often heritable and plastic at the same time. Indeed, behaviors that reflect an individual's personality can respond to environmental factors or change with age. To date, little is known regarding personality changes during a wild animals' lifetime and even less about stability in heritability of behavior across ages. In this study, we investigated age‐related changes in the mean and in the additive genetic variance of exploratory behavior, a commonly used measure of animal personality, in a wild population of great tits. Heritability of exploration is reduced in adults compared to juveniles, with a low genetic correlation across these age classes. A random regression animal model confirmed the occurrence of genotype–age interactions (G×A) in exploration, causing a decrease in additive genetic variance before individuals become 1 year old, and a decline in cross‐age genetic correlations between young and increasingly old individuals. Of the few studies investigating G×A in behaviors, this study provides rare evidence for this phenomenon in an extensively studied behavior. We indeed demonstrate that heritability and cross‐age genetic correlations in this behavior are not stable over an individual's lifetime, which can affect its potential response to selection. Because G×A is likely to be common in behaviors and have consequences for our understanding of the evolution of animal personality, more attention should be turned to this phenomenon in the future work.
Highlights
Behaviors are labile traits, which by definition can be adjusted by individuals in response to variations in external fac‐ tors and internal factors such as age
The univariate animal model with all ages and sexes pooled showed that exploratory behavior was heritable in this population (h2 = 0.17, SE = 0.04) and that there was a significant quadratic effect of age and season but no significant difference between the sexes (Table 2)
Univariate models in juveniles and adults separately showed that exploratory behavior was significantly heritable in juveniles (h2 = 0.31, SE = 0.06, CVA = 6.96, Likelihood Ratio Test (LRT) test: χ2 = 21.95, df = 1, p < 0.001) but not significantly heritable in adults (h2 = 0.15, SE = 0.11, CVA = 3.32, LRT test: χ2 = 2.59, df = 1, p = 0.11) (Tables S1 and S2)
Summary
Behaviors are labile traits, which by definition can be adjusted by individuals in response to variations in external (biotic, abiotic) fac‐ tors and internal factors such as age. G×A is a process that can impact the evolution of any trait by inducing changes in heritability across ages and ge‐ netic correlations between traits, thereby altering their responses to selection (Lynch & Walsh, 1998) This process is particu‐ larly interesting in the context of aging because it is considered as the “fingerprint” of evolved senescence (Charmantier, Brommer, & Nussey, 2014) and age‐related changes in additive genetic variance of life history traits have been reported in wild animal populations (reviewed in Charmantier et al, 2014) and in plants (Pujol, Marrot, & Pannell, 2014). We show that additive genetic variance decreases to become nonsignificantly different from zero before individuals reach their first year and that this rapid reduction in additive genetic variance is not due to the selective disappearance of certain juveniles based on their exploration
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