Time and Energy Costs of Aggression in Testosterone-Implanted Free-Living Male Mountain Spiny Lizards (Sceloporus jarrovi)

Abstract

Several lines of evidence support the hypothesis that free-living male mountain spiny lizards (Sceloporus jarrovi) given testosterone (T) implants experience increased energetic costs as a result of increased territorial aggression. More aggressive T-implanted males expended more energy by having a longer daily activity period andperforming more territorial displays and movements. T-implanted males made fewer foraging attempts, caught fewer insects, and had lower gut content mass. The change infrequency of foraging attempts suggests a time conflict between territorial aggression and foraging. T-implanted males also had less stored energy in the form of neutral lipids and lower dry lean body mass for their snoutvent lengths. Decreased lean body mass suggests that T-implanted males may be trading increased aggression for decreased growth. These data suggest that energetic considerations could explain previously observed decreases in survivorship of T-implanted males. Survivorship diferences, however, may al...