The interplay between environment, aggression and fitness in a free living vertebrate

The association between phenotypic variation and environmental variation is a central theme in evolutionary biology as it reflects the way in which organisms adapt to their surrounding environment. Behaviour is a key factor mediating an individual’s interaction with its environment. Therefore, how individuals behaviourally respond to their environment potentially has important consequences for individual fitness and population dynamics. Aggression in particular is both influenced by, and influences, an individual’s physical environment and individual differences in aggression have strong and persistent effects on fitness-related traits. We examined the links between environment, individual aggression, and fitness in a social lizard species Egernia whitii. We found that there was an association between aggression and temperature, with more aggressive individuals occurring in warmer habitats. We suggest that this is a result of more aggressive individuals being better competitors for these high quality areas. In terms of reproductive output, the importance of male aggression in this system appears to be context-dependent: in resource limited areas, more aggressive males had a higher reproductive output than less aggressive males. Male reproductive output in high resource areas did not appear to be aggression dependent. Female reproductive effort was determined by the amount of rock cover in her territory and her aggression. This study represents a first step in disentangling the complex relationships between environmental variation and individual behavioural variation in determining fitness and population dynamics.