Behavioural syndromes, syndrome deviation and the within- and between-individual components of phenotypic correlations: when reality does not meet statistics

Abstract

Evolutionary mechanisms leading to correlations across different behaviours, called behavioural syndromes, are hard to study, mostly because behavioural syndromes are group/population level phenomena. Recently (Herczeg and Garamszegi Behav Ecol Sociobiol 66:161-169, 2012), we introduced the concept of syndrome deviation that allows the study of behavioural syndromes at the individual level by focusing on the individual deviation from the hypothetical perfect group-level behavioural correlation. Subsequently, Dingemanse et al. (Behav Ecol Sociobiol 66:1543-1548) emphasized that behavioural syndromes refer to the between-individual component of phenotypic correlations, and only this component is relevant for syndrome deviation. They also recommended mixed models to decompose the between-and within-individual correlations. We agree that separating these components is important, but the proposed approach is impractical to apply for functionally different behaviours because (1) the assumption of constant within-individual correlations is unjustified and (2) different behaviours cannot be measured at the same time. Further, our simulations based on mixed models show that the statistical differentiation between the within-and between-individual components is inefficient when using realistic sample sizes. Until the separation of between-and within-individual correlations is resolved, we recommend alternative approaches for empirical behavioural syndrome research that consider the repeatability of the behaviours and the optimal balance between within-and between-individual sample sizes. Syndrome deviation calculated from phenotypic correlations of traits that are proven to be individual specific, or from the betweenindividual correlations if possible, is a meaningful metric to describe behavioural consistency and to explain its evolutionary significance.

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“…However, it is clear that (1) animal personality and behavioral syndrome can have different developmental routes and thus (2) probably different functions and adaptive values too. This result reinforces the need to separate the two levels of behavioral consistency (Garamszegi and Herczeg ; Jandt et al. ).…”

“…Studying behavioral consistency has recently become a central topic of evolutionary behavioral ecology, aiming to understand the evolutionary and developmental mechanisms behind consistent individual differences in behavior. Behavioral consistency can be approached and quantified at two levels (Garamszegi and Herczeg ; Jandt et al. ; Urszán et al.…”

“…): First, individuals can consistently differ in certain behaviors (in aggression, for instance), and second, individuals can consistently differ across two or more functionally different behaviors (across aggression, exploration, and risk‐taking, for instance). The first form of behavioral consistency is statistically approached via repeatability, and called animal personality, while the second is approached via correlation, and called behavioral syndrome (Garamszegi and Herczeg ; Jandt et al. ; Urszán et al.…”

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“…Interindividual consistency in behavioural tendencies are almost ubiquitously recognized across taxa (reviewed in Gosling, 2001; Réale, Reader, Sol, McDougall, & Dingemanse, 2007), with individuals differing in a variety of behavioural traits (reviewed in: Carter, Feeney, Marshall, Cowlishaw, & Heinsohn, 2013; Dall, Houston, & McNamara, 2004; Réale et al, 2007). If an individual displays consistency in a single behaviour over time or in different contexts, it is termed a ‘personality’ trait, whereas consistency in the relationship between two or more functionally different behaviours is termed a ‘behavioural syndrome’ (Garamszegi & Herczeg, 2012). The presence of personality traits and behavioural syndromes implies that an individual is constrained to a limited number of behavioural responses, creating cost–benefit trade-offs (Kelley, Phillips, & Evans, 2013) that can influence survival (Dingemanse, Both, Drent, & Tinbergen, 2004; Downes, 2002; Smith & Blumstein, 2008), reproductive success (Both, Dingemanse, Drent, & Tinbergen, 2005; Pruitt & Ferrari, 2011; Sih & Watters, 2005) resource acquisition (Webster, Ward, & Hart, 2009) and growth (Meekan, von Kuerthy, McCormick, & Radford, 2010).…”

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“…Martin et al . ; Garamszegi & Herczeg ; van de Pol ; Dingemanse & Dochtermann ; Araya‐Ajoy, Mathot & Dingemanse ; Kain, Bolker & McCoy ). Given the many possible biological questions that one may ask (e.g.…”