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This chapter discusses the potential benefit of using the selectionist approach to study human and animal personality traits. It first briefly introduces the selectionist approach, describes the methods proposed to run multivariate selection analyses, and follows with a review of the most recent results showing how animal personality scientists are beginning to apply this method to test the fit of evolutionary scenarios for the maintenance of variation in personality traits. Finally, it reviews the evidence from recent studies on human personality suggesting that selection can indeed affect personality dimensions. Not every scenario will apply equally to humans and animals. However, it is assumed that humans and many animals broadly face the same types of ecological challenges that they must cope with. Therefore, studies on both human and non-human animals are likely to provide a general explanation for the maintenance of individual variance in personality traits.

This chapter addresses the quantitative and molecular genetics of animal personality. It discusses the role of additive and nonadditive genetic effects, genetic correlations between animal personality traits, and modes of development and heritability. The chapter also presents a formal meta-analysis of published studies on the heritability of personality estimates of animal traits.

This chapter discusses the benefits of animal personality studies for understanding human personality. It first reviews animal personality studies across different species and then illustrates the benefits of taking a comparative perspective in personality research. The chapter also discusses some basic principles for making cross-species comparisons in personality psychology.

Animal personality has been demonstrated in a wide range of taxa, including crustaceans. This chapter defines personality as consistent variation in behavior among individuals. It describes related ideas about how individuals can differ in the way they adjust their behavior to match the current situation (“behavioral plasticity”) and how they might differ in how consistent their behavior is within a particular situation (“within individual variation”). Such behavioral variation may represent a component of wider syndromes encompassing among-individual differences in life history traits such as growth, metabolism, and fecundity. First, the chapter reviews studies that have tested these ideas in a range of crustacean species. It then focuses on a series of studies on the common European hermit crab Pagurus bernhardus. In both cases, it describes details of the experimental approaches and analyses used to study personality in crustaceans. While boldness appears to be a key personality trait in hermit crabs and other crustaceans, bold individuals are not necessarily those with the greatest success in acquiring resources or with the greatest life history productivity (i.e., investment in growth and reproduction). Rather, individuals that win fights and invest heavily in respiratory pigments and in reproduction appear to behave consistently more cautious when compared to other individuals from the same population. Despite these initial findings, there is a paucity of studies that investigate links between personality and mating behavior in crustaceans, or that investigate the behavior of females; these areas should be priorities for future work.

Over the last decade, the study of consistent individual-level differences in behaviour, or animal personality, has become a subject of significant research growth. This ongoing interest in personality traits is likely attributable to the diverse range of taxa as well as ecological contexts in which personality has been shown to be mechanistically involved. Despite this research interest, surprisingly little is known about the role of personality in terms of complex social interaction dynamics and group-level interactions such as those characterized by social networks. The aim of this chapter is to highlight recent advances in the integration of personality and network analysis research and provide an overview of areas of current and future research promise. This chapter discusses the potential importance of key individuals, or individuals with particular behavioural characteristics (i.e. behavioural types) in animal social networks as well as the need for considering networks and personality over ontogeny and related processes. Lastly, this chapter offers new directions and perspectives for future research on this exciting topic.

This chapter focuses on evolutionary causes of animal personalities. First, it discusses the causes of variation within populations, and, in particular, describes how state differences, frequency-dependent selection, spatiotemporal variation in the environment, and non-equilibrium dynamics can cause variation in behavior. The chapter also examines the role of the architecture of behavior, stable state variables, and social conventions in causing adaptive behavioral correlations.

This chapter explores the relationship between physiological and behavioral traits commonly considered in animal personality assessments, discussing the physiological responses to stress and the activity of the hypothalamic-pituitary-adrenal axis (HPA), the sympatho-adrenomedullary pathway (SAM), and the hypothalamic-pituitary-gonadal axis (HPG). It also presents evidence on linking the neurotransmitters serotonin and dopamine, as well as cortical brain structures such as the hippocampus, to behavioral variations.

Emerging interest on the part of behavioural ecologists into the causes and consequences of individually repeatable behaviour substantially crosses over methodology and theory well developed in the field of quantitative genetics. Unfortunately, how behavioural ecological concepts translate to quantitative genetic parameters has been under-recognized by researchers in both groups. In this chapter, this overlap is discussed, behavioural ecology terms like ‘animal personality’ and ‘behavioural syndrome’ explicitly defined as quantitative genetic parameters, and adaptive explanations for between-individual behavioural variation are also examined. In addition, this chapter talks about what is known about patterns of behavioural heritabilities, additive genetic correlations between behaviours, and how behavioural correlations might constrain evolutionary responses. Finally, this chapter describes ways in which theory and empirical research in behavioural ecology might inform attempts among the broader quantitative genetics community to understand how and why variation is distributed.