Lovers and fighters in sleepy lizard land: where do aggressive males fit in a social network?

In this study we explored relationships between the aggressiveness of male sleepy lizards, Tiliqua rugosa, and their position in a social network. We attached activity loggers to 60 neighbouring lizards during the activity season (September–December) in 2009 at a study site in the mid-north of South Australia. The loggers continuously recorded the activity and location of lizards, allowing us to infer direct social associations. We calculated pairwise associations and integrated these into a social network and calculated node-based measures that quantified male–male and male–female interactions. Aggressiveness of males was quantified in two ways; by involvement in a fight, as indicated by the presence of fresh scale damage, and by aggression assays that scored the response of lizards to conspecific and predator cues. More aggressive lizards in these assays were more likely to be found with fresh scale damage in field surveys. Less aggressive males were more strongly connected to females in the network, and were more commonly in contact with their monogamous female partner, than more aggressive males. Our results suggest a behavioural syndrome among male lizards connecting level of aggression and association with females, with a divergence in behaviour; lovers that are strongly paired and nonaggressive, and fighters that are weakly associated with females and more aggressive.