Mather, J. A., Carere, C. 2019. Consider the individual: Personality and welfare in invertebrates. In: The Welfare of Invertebrate Animals. Carere, C., Mather, J. (eds), 229-245. Springer, Cham.

Personality, defined as consistent between-individual variation in clusters of behavioral traits independent of factors such as age or sex, emerges in most animal species tested so far. The number of invertebrate species discovered to have clear personality profiles is rapidly increasing. This previously neglected variation harbors many unsolved questions about its evolutionary maintenance and consequences, as well as about underlying proximate mechanisms, and it relates to the way individuals cope with stress behaviorally and physiologically. Importantly, it poses new challenges about welfare consequences, since the individuals emerge as the primary target of assessment and adjustment, and not the species. In fact, the effect of individual personalities on suitability for captivity and the efforts necessary to accommodate individuals of any given invertebrate species have not been considered, despite some anecdotal evidence from keepers, e.g., in octopuses, indicating its potential relevance. After an overview on what personality is and why this concept may be relevant to welfare, we enlist challenges and opportunities offered by invertebrates by presenting a series of case studies: cnidarian aggression, spider sexual cannibalism, cephalopod enrichment and escape, and colony personality in social insects. We conclude that because animals of many invertebrate phyla have distinct personalities, fine-tuning welfare provisions to what suits the individual best is recommended.