Spatiotemporal variation in the environment generates uncertainties regarding physiological or behavioural decisions that will affect the fitness of organisms. Information about environmental parameters may reduce this uncertainty, allowing receivers to adjust their responses. When environmental variation is so high that the information cannot be transferred genetically or prenatally, other mechanisms such as information gathering should evolve. This possibility encompasses three sources of information: personal information obtained by direct interaction with the environment using trial-error tactics (Valone 1991), the presence of conspecifics, which may indicate habitat suitability (Stamps 1988), and socially acquired information obtained by observing the behaviour of others (Giraldeau et al. 2002). It is known that the use of these types of information may impart different types of benefits as well as costs (Dall et al. 2005; Kendal et al. 2005). Therefore, it is worth exploring the potential costs and benefits associated with the use of these sources of information for understanding the causes and consequences of social influences on behavioural decisions. Different species, sexes or phenotypes might be subjected to different cost : benefit ratios depending on key factors such as the costs of information sampling, the costs of competition for the target resource and the success of resource detection (Danchin et al. 2001; Giraldeau et al. 2002; Nocera et al. 2006; Pasinelli et al. 2007). Relying on the behaviour of conspecifics which are exploiting the target resource should impart higher success in detection and lower searching time than relying on trial-error tactics or on the conspecific presence regardless of their activity. On the other hand, making use of social information from conspecific behaviour may also increase the competition level when individuals are simultaneously exploiting the same resource. Thus, it is expected that animals should use one or more of these information types only when the benefits exceed the costs (Dall et al. 2005; Kendal et al. 2005). Theoretical and empirical studies have focused mainly on the costs inherent to the gathering of social information, such as incompatibility with personal information (Giraldeau et al. 2002), or increased predation risk (Coolen et al. 2003). However, the costs arising after the choice, such as costly interactions with conspecifics when simultaneously exploiting the target resource, have been rarely considered (Danchin et al. 2001; Seppanën et al. 2007).
Behavioural differences between sexes arising from cost : benefit ratio differences has been reported across taxa, such as antipredatory behaviour (Bernal et al. 2007; Cooper & Wilson 2007), foraging (Magurran & Maciás-Garcia 2000; Beck et al. 2007) or aggressiveness (Rosvall 2008). Specifically, competition is often higher within sexes than between sexes, and the intensity of intrasexual competition is often sex-biased (Magurran & Maciás-Garcia 2000; Clutton-Brock 2007). Thus, it is expected that when there are inter- and intrasexual differences in the competition level, males and females might use the information types differently depending on the balance between costs and benefits. However, given sex differences across taxa in many life-history traits besides behaviour (Van Damme et al. 2008) there is surprisingly little evidence of sex-dependent influence on the use of social information (Doligez et al. 1999; Aragón et al. 2006a; Nocera et al. 2006), and it is lacking in a foraging context. We can use theory to predict that while intra-male competition involves the access to mates, females compete with each other for resources that allow them to increase their reproductive output, such as breeding sites, parental care, social rank or food (Summers 1989; Holekamp et al. 1996; Magurran & Maciás-Garcia 2000; Rosvall 2008). Depending on the cost : benefit ratio of intrasexual competition for mates or other resources, selective forces would favour aggressiveness in the sex that gains important benefits from costly interactions (Clutton-Brock 2007; Rosvall 2008).
Many studies on socially acquired information have focused on conspecific foraging activities as a source of information about when, where, what, and how to eat. This has been showed to occur for a variety of bird (Valone & Templeton 2002), mammal (Galef & Giraldeau 2001) and fish species (Coolen et al. 2003). In amphibians, social foraging has recently been documented (Sontag et al. 2006). The goals of this study are: (i) to examine whether the response of Bosca's newt, Lissotriton boscai, to different combinations of information types in a foraging context is sex-dependent, and (ii) to resemble the conditions inherently associated with the choice of using information on feeding conspecifics, and test whether the level of competition for the limited source of food is sex-dependent. In the first experiment, I tested the time elapsed to eat food items when an individual was confronted with personal information in the presence of food, with the combination of a conspecific presence and food, and with the combination of a conspecific actually eating and food. I performed a second experiment to examine the potential costs associated with direct competition for limited food in clumped conditions, measuring the time that individuals spent in close proximity and the degree of agonistic interactions. It is expected that eating in close proximity would promote social interactions.
I selected L. boscai as a model of an amphibian because: (i) it is found in high densities in most of its geographic distribution (Montori & Herrero 2004) and social interactions between individuals in the aquatic phase are frequent (e.g. Mouta-Faria 1995), (ii) individuals inhabit shallow and slow-running clear water where visual communication is favoured, but abundant aquatic vegetation may hinder prey detection (Montori & Herrero 2004), (iii) the success of food intake (the location of which is unpredictable) may be crucial in this species since individuals have to survive first the summer when they enter dormancy, and then the winter when prey abundance decreases, and (iv) the feeding behaviour of this species is visually conspicuous.