Within‐Individual Correlations Reveal Link Between a Behavioral Syndrome, Condition, and Cortisol in Free‐Ranging Belding's Ground Squirrels

Abstract

Animals often exhibit consistent individual differences in behavior (i.e. animal personality) and correlations between behaviors (i.e. behavioral syndromes), yet the causes of those patterns of behavioral variation remain insufficiently understood. Many authors hypothesize that state-dependent behavior produces animal personality and behavioral syndromes. However, empirical studies assessing patterns of covariation among behavioral traits and state variables have produced mixed results. New statistical methods that partition correlations into between-individual and residual within-individual correlations offer an opportunity to more sufficiently quantify relationships among behaviors and state variables to assess hypotheses of animal personality and behavioral syndromes. In a population of wild Belding's ground squirrels (Urocitellus beldingi) we repeatedly measured activity, exploration, and response to restraint behaviors alongside glucocorticoids and nutritional condition. We used multivariate mixed models to determine whether between-individual or within-individual correlations drive phenotypic relationships among traits. Squirrels had consistent individual differences for all five traits. At the between-individual level, activity and exploration were positively correlated whereas both traits negatively correlated with response to restraint, demonstrating a behavioral syndrome. At the within-individual level, condition negatively correlated with cortisol, activity and exploration. Importantly, this indicates that although behavior is state-dependent, which may play a role in animal personality and behavioral syndromes, feedback mechanisms between condition and behavior appear not to produce consistent individual differences in behavior and correlations between them.

Evidence for a mechanism of phenotypic integration of behaviour and innate immunity in a wild rodent: implications for animal personality and ecological immunology

“…1). Although this result supports the hypothesis that GReCORT binding is a mechanism of plasticity for exploration, it is not matched by a significant relationship between CORT and exploration in free-ranging squirrels (Dosmann et al, 2015). Because we controlled for multiple comparisons, it is unlikely that this discrepancy is due to a type I error (Nakagawa, 2004).…”

“…Although this relationship was not significant, these results are interesting when considered together because the three behavioural traits constitute a behavioural syndrome in free-ranging squirrels. These behavioural traits covary between and within individuals (Dosmann et al, 2015). Although our sample size in this experiment was too small to statistically partition variation into within-and between-individual components, our experimental design indicates that the treatment effect was at the within-individual level.…”

“…In squirrels, activity, exploration and response to restraint constitute a behavioural syndrome (Dosmann et al, 2015). CORT positively relates to activity when squirrels are in good condition (Dosmann et al, n.d.) and treatment with exogenous CORT decreases BKA (Brooks & Mateo, 2013).…”

“…Belding's ground squirrels exhibit a behavioural syndrome (Dosmann, Brooks, & Mateo, 2015), and relationships among CORT, behaviours and immunity in the species open questions about whether GReCORT binding is a mechanism accounting for patterns of (co)variation of behaviour and immunity. CORT levels of squirrels vary with environmental variables such as habitat features and predation threat (Mateo, 2007(Mateo, , 2010, meaning that phenotypic responses to changes in CORT can be interpreted in terms of plasticity.…”

“…In this study, we measured four behavioural traits of squirrels: activity, exploration, antipredator behaviour and response to restraint, as well as a functional measure of constitutive innate immunity, bacteriakilling ability (BKA). Activity, exploration and response to restraint comprise a behavioural syndrome in free-ranging Belding's ground squirrels, with activity and exploration positively correlating at the between-individual and within-individual level while both behaviours negatively correlate with response to restraint at the between-individual level (Dosmann et al, 2015). In addition, CORT and body condition have an interactive effect on squirrels' activity, with squirrels in good condition showing a positive relationship between CORT and activity (Dosmann, Brooks, & Mateo, n.d.).…”