War and peace: plasticity of aggression and the social context of displays in male Australian Water Dragons

Detailed behavioral observations of the same urban population of Water Dragons (Intellagama lesueurii) during two reproductive periods 7 years apart (2009 vs. 2016) revealed a dramatic change in aggression and the social context of male displays. Differences in the behavior of 2016 males may be a consequence of increased visibility of conspecifics due to anthropogenic removal of vegetation, however, the density of lizards was also lower in 2016 than in 2009. No males, and only 19.4% of females present in 2009 survived to 2016. Males present in 2016 tended to be smaller, and had significantly smaller heads relative to body size. They engaged in fewer aggressive contests but held larger territories. Responses to perturbation of social hierarchies (by experimental removal of rival territory owners and spontaneous take-overs by male challengers) were less intense than in 2009. Unlike 2009 males that gave more displays when contesting rivals, 2016 male territory owners gave proportionally more displays when interacting with females. We attribute these shifts in male aggression and display context to altered potential for long-range signaling. Our results reinforce the point that social behavior in lizards can be highly flexible, and that changes in environmental factors may elicit such shifts. Thus, short-term studies of social behavior—even if conducted in great detail—may fail to capture the full range of behavioral plasticity that can be exhibited over longer periods.