Abstract
While the literature on consistent individual differences in correlated suites of physiological and behavioural traits is steadily growing for vertebrates, invertebrates have received less attention. The few studies that do exist have measured temporary physiological states (or responses), rather than consistent individual physiological traits. Here, I explore the consistency of individual differences in physiology and behaviour of n=53 shore crabs (Carcinus maenas) by repeatedly measuring haemolymph density (HD) and the crabs' responses to a novel environment. In crustaceans, HD is directly proportional to protein concentrations, and thus indicative of physiological condition. HD was highly repeatable, and crabs showed consistent individual differences in their behavioural responses to a novel environment, thus indicating individual consistency in both physiology and behaviour. Furthermore, HD was significantly correlated with the crabs' risk propensity, i.e. individuals with higher HD spent more time near shelter. Overall, this provides the first evidence for consistency in an endogenous physiological trait in an invertebrate. The link between consistent physiology and behaviour, i.e. coping styles, analogous to those found in vertebrates, suggests metabolic and/or immunological correlates of personality which offer great potential for future studies.
Highlights
Animal personalities, i.e. consistent individual differences in behaviour, have been extensively studied in vertebrates (e.g. [1,2]) and more recently, in invertebrates
Relationships between individual differences in behaviour and physiology have been documented in invertebrates, and previous studies have focused on life-history variables (e.g. Acyrthosiphon pisum [8], Euprymna tasmanica [9]), parasite load (e.g. [10]), immune parameters (e.g. Gryllus spp. [11]), and effects of environmental conditions, e.g. food quality (e.g. Phaedon cochleariae [12]) or temperature (e.g. Pagurus bernhardus [13], Ozius truncatus [14])
Three behavioural measures were extracted from video: (i) Exploration (the percentage of test arena explored, assessed by drawing a square grid on tracking trajectories images, obtained using the EthoWatcher R Tracking Module [19] and counting the number of squares visited by the crab), (ii) Immobility and (iii) Risk propensity
Summary
I.e. consistent individual differences in behaviour, have been extensively studied in vertebrates (e.g. [1,2]) and more recently, in invertebrates (reviewed by Mather & Logue [3] and Kralj-Fišer & Schuett [4]). I.e. consistent individual differences in behaviour, have been extensively studied in vertebrates [5,6,7]) Such ‘coping 2 styles’, that is consistent individual differences in correlated suites of behavioural and physiological traits [5], provide a useful concept for understanding individual adaptive capacity to deal with changes in the environment (note that, misleadingly, ‘coping style’ is sometimes used in the literature as a synonym for personality without inferring a link between physiology and behaviour). In all of these examples, researchers have investigated and measured ‘temporary’ physiological states (or physiological responses), which they linked to behaviour, rather than measuring consistent individual differences in an endogenous physiological trait. [15,16]), and to my knowledge no study has yet assessed consistent individual differences in an invertebrate endogenous physiological trait Individual consistency, or repeatability, in a trait can only be assessed by obtaining multiple measures from the same individuals (e.g. [15,16]), and to my knowledge no study has yet assessed consistent individual differences in an invertebrate endogenous physiological trait
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