Benefits and costs of parental care

Abstract

In order to explain the huge variation in parental behaviour, evolutionary biologists have traditionally used a cost–benefit approach, which enables them to analyse behavioural traits in terms of the positive and negative effects on the transmission of parental genes to the next generation. Empirical evidence supports the presence of a number of different trade-offs between the costs and benefits associated with parental care (Stearns 1992; Harshman and Zera 2007), although the mechanisms they are governed by are still the object of debate. In fact, Clutton-Brock’s (1991) seminal book did not address the mechanistic bases of parental care and most work in this field has been conducted over the last 20 years. Research on mechanisms has revealed that to understand parental care behaviour we need to move away from traditional models based exclusively on currencies of energy or time. Despite repeated claims, the integration of proximate mechanisms into ultimate explanations is currently far from successful (e.g. Barnes and Partridge 2003; McNamara and Houston 2009). In this chapter we aim to describe the most relevant advances in this field. In this chapter, we employ Clutton-Brock’s (1991) definitions of the costs and benefits of parental care. Costs imply a reduction in the number of offspring other than those that are currently receiving care (i.e. parental investment, Trivers 1972), whereas benefits are increased fitness in the offspring currently being cared for (see also Chapter 1). Benefits may be derived directly from resources allocated to the offspring (e.g. food, temperature), indirectly from protection against predators, or from the modification of the environment in which the offspring are developing (Chapter 1). We begin this chapter by reviewing the traditional idea of resource allocation trade-offs, and also explore how trade-offs need not be based on resources, and the relevance of cost-free resources. We then analyse in more detail studies of the benefits and costs of parental behaviour and, above all, work that combines mechanistic and functional explanations. Finally, we address the control systems that translate cues perceived by the organism about costs and benefits allowing individuals to take decisions.