Summary

Reptiles, especially sexually selected lizards, have proven to be good model systems for studying the evolution of contest competition. Aggression, especially by males, plays an important role in structuring reptilian social systems often characterised by territorial defence and both fixed and plastic alternative male tactics. Reptilian aggressive behaviour ranges from overt physical attacks that are likely to require significant energy expenditure and risk of injury to less costly signalling using visually conspicuous stereotypical motor patterns, striking colouration and chemical cues. Morphological traits that promote success in aggressive contests involve development of exaggerated and specialised physical armaments, colour conspicuousness, as well as whole animal performance traits and large overall size. Aggressive behaviour patterns may also be influenced by body temperature, prior social experience and other social variables that affect the context of social interactions. Lizards especially are important models for tests of both the proposed influence of hormones on aggression, as well as the possible effects of aggression on hormone levels. Lastly, lizards have also been used to test the extent to which game-theoretic models can be used to explain the evolutionary maintenance of alternative colour/behaviour morphs and the outcome of dyadic aggressive contests.

Introduction

Extant vertebrates commonly known as ‘reptiles’ actually include three lineages that are related only distantly (Zug et al. 2001, Vitt & Caldwell 2009). Although the fossil record suggests fascinating hypotheses pertaining to intraspecific aggression in some extinct reptiles (e.g. Hieronymus et al. 2009, Peterson et al. 2009), for obvious reasons, research on contest behaviour has focused on extant forms. For this chapter, ‘reptiles’ thus refers to the extant members of three clades: Crocodilians (alligators and crocodiles), Chelonians (turtles) and, especially, the Lepidosauria (tuataras, lizards and snakes).