The behavioural ecology of animal signalsa functional theoretical perspective and its application to the study of scent marks in the lizard podarcis hispanica

Resumen

The focus of this PhD dissertation is the adaptive value of animal signals. Its scope is both theoretical and empirical, as are its main objectives. This duality is reflected in its two constituent parts. In the first one ('towards a functional theoretical framework of animal communication') we discuss the existence of a duality in the function of animal signals (i.e. to serve both sender and receiver's interests) and explore whether this duality can be understood without the notion of information. Against recent proposals to abandon the concept and downplay its importance for the study of animal communication, we argue that the adoption of an objective 'functional' definition of information results in a more comprehensive theoretical framework with significant advantages. Besides, a definition of communication couched in terms of functional information is better equipped to deal with the extraordinary diversity of animal signals, it facilitates the distinction of informative and deceptive signals, and it accommodates a number of conceptual and practical issues (e.g. redundancy, alerting components) that are lost when we fail to acknowledge the informative content of animal signals. A functional definition of information redefines animal signals (and therefore animal communication) in such a way that it brings the notion of information under the adaptationist umbrella, resulting in a comprehensive theoretical framework of animal communication. The second part of this dissertation follows the theoretical framework laid down in the first part, and is a mostly empirical investigation into the function of scent marks in the Iberian wall lizard (Podarcis hispanica). Chemicals deliberately deposited in the environment in the form of scent marks are among the most ubiquitous social signals in terrestrial vertebrates, but their actual function is still largely unknown. Our findings support the hypothesis that scent marks in Podarcis hispanica, and probably in most territorial lizards, have evolved into social signals by minimizing the costs of territorial defence (to the benefit of both senders and receivers), and by allowing receivers to extract complex functional information that is crucial to their reproductive success (i.e. territory ownership, rival competitive ability, territory quality, individual identity, potential threat). The results reported in this thesis represent a substantial contribution to our understanding of social communication in lizards, and suggest that lizard territorial behaviour is as complex and sophisticated as in other vertebrates, such as mammals and birds. Finally, we investigate the potential role of scent marks as signals mediating female mate choice in lizards. Over the last few years, a diversity of studies have argued pro and against the existence of female mate choice in different lizard species, and new hypotheses have been put forward to explain why there is apparently good evidence of female mate choice in some lizards, while it is seemingly absent or of little importance in many others. In response to this surge of new evidence, we conduct a critical review of the new evidence for the existence of female mate choice in lizards, and follow it with an empirical investigation into the potential role of scent marks as quality signals mediating female mate choice in Podarcis hispanica. Our meta-analysis of the literature shows that female choice is not frequent in lizards, and that it is particularly rare in territorial species, where the costs of female choice are bound to be particularly high. The results obtained in our experiment of female choice point in the same direction, and strongly argue against the existence of female mate choice in a typical territorial lacertid lizard, Podarcis hispanica. All in all, the results presented in this thesis suggest that scent marks have evolved in P. hispanica in response mainly to intra-sexual selection pressures, a result that will likely apply to many other lizard species.