Development, Ontogeny and Parasite-Mediated Changes in Social Behaviour

Abstract

Tinbergen (1963) identified the development of a behavioural trait during an animal’s lifetime as one of the four key questions that should be asked about a given trait in order to understand it. The study of the development, or ontogeny, of sociality throughout animals’ lives provides an insight to both the mechanisms of sociality and its functions. In this chapter, we examine first the development of sociality. Many animal species spend the initial stages of life in a social environment, for example, if eggs are clustered or young are born into a litter of sibs. This means that an aggregation of a cohort of kin is formed. These may subsequently go on to form a true social group, based on social attraction, or they may simply remain together through philopatry, and it can be difficult to distinguish between these. Nonetheless, the development of social attraction to conspecifics in early life has been examined in a few species in conjunction with the development of sensory and locomotive capabilities, and we describe these here. Once the ability to identify and locate conspecifics is developed, then the likelihood of an animal seeking out others of its kind in order to associate with them and to form groups is governed by a range of factors. These include the early-life social environment of offspring, the neural development of individuals, the action of hormones and the genetic predisposition of animals to sociality. We consider each of these in relation to the development and expression of sociality and further how this relates to the ecological context in which the animal operates. Following on from this, we consider how parasitism, a near ubiquitous reality for free-ranging animals, affects patterns of association among animals.