Date of this Version
Published in Animal Signaling and Function: An Integrative Approach, First Edition. Edited by Duncan J. Irschick, Mark Briffa, and Jeffrey Podos. Published 2015 by John Wiley & Sons, Inc.
Animal signaling is commonly thought to be costly. Signaling costs can arise via a variety of avenues, including energy expenditure, predator attraction, and so on (reviews in Zuk and Kolluru, 1998; Kotiaho, 2001), and are predicted to increase with signal expression (e.g., size, amplitude, and intensity; Johnstone, 1997). Due to these costs, signaler condition, which is hypothesized to be a reflection of a signaler’s genetic quality, is expected to influence the level of signal expression one can afford (Zahavi, 1975), resulting in a positive correlation between signaler condition and signal expression – that is, condition-dependent signaling (Zahavi, 1977; West-Eberhard, 1979; Andersson, 1982; Nur and Hasson, 1984; Zeh and Zeh, 1988; von Schantz et al., 1999). Despite the wealth of theoretical and empirical work on condition-dependent signaling, the term condition itself is somewhat enigmatic. An individual’s condition is a theoretical construct associated with the acquisition and allocation of nutritional resources, and is assumed to be an integral part of an individual’s health, vigor, and viability (Andersson, 1982; Nur and Hasson, 1984; Zeh and Zeh, 1988). Condition is often thought of as polygenic in nature, capturing much of the additive genetic variance responsible for viability, spanning numerous loci across the genome (Andersson, 1982; Rowe and Houle, 1996); however, like other quantitative traits, condition is also influenced by the environment as well as by interactions between an individual’s genotype and the environment (Hunt et al., 2004b). In this chapter, we use a widely accepted working definition of condition provided by Rowe and Houle (1996)−a pool of resources acquired from the environment, which is available for allocation to various fitness-related traits (see Figure 9.1). An individual’s condition sums numerous processes throughout its lifespan and is constantly fluctuating as resources are acquired and allocated to different functions (Figure 9.1). This broad definition of condition incorporates information on the resources available throughout an individual’s life−it encompasses the resources used during development to create structures (including those used for resource acquisition), the resources used in the normal functioning of an individual (i.e., its physiology), and the resources currently available in an individual’s energy stores (Figure 9.1). The decisions directing resource acquisition and allocation strategies (Figure 9.1) are ultimately influenced by both an individual’s environment (e.g., presence/absence of predators and food abundance) and its genotype (e.g., heritable traits related to foraging ability, digestion, and learning).