Effects of testosterone on locomotor performance and growth in field-active northern fence lizards, Sceloporus undulatus hyacinthinus.

The role of steroids in locomotor performance and growth was examined in free-living lizards. Male northern fence lizards (Sceloporus undulatus hyacinthinus) with experimentally elevated plasma testosterone concentrations had greater sprint speed (+24%) and burst stamina (+17%) than sham-implanted males after 14-23 d in the field. This enhanced performance was associated with significant energetic costs, as the testosterone-implanted lizards had reduced growth rates, and, in a companion experiment, field-active testosterone-implanted lizards had smaller fat-body masses than controls after just 3-4 wk. These results suggest that, in addition to influencing a variety of behavioral and morphological traits, testosterone may play an important role in the regulation of locomotor performance. Also, natural levels of locomotor performance may be constrained, in part, by associated costs of elevated plasma testosterone concentrations.