Effects of Testosterone on Bite Force and Locomotor Performance in the Six-Lined Racerunner

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Numerous studies have examined the effects of testosterone on behavior in territorial lizards, but few have explored the role of testosterone (T) in non-territorial species. Here, we experimentally manipulated T levels in Aspdidoscelis sexlineatus, a common non-territorial lizard. During the breeding season, males exhibit mate guarding, and will follow a female for several days after copulation. Male-to-male interactions during the breeding season involve chasing and occasionally escalate into fights with biting. Therefore, high bite force and high endurance capacity should be advantageous to retain exclusive access to females and ensure paternity. In territorial lizards, T levels peak with the breeding season and several studies have cited T as a possible mediator of the seasonal increases in performance (e.g. bite force and locomotor performance). Fluctuating T levels have been observed in A. sexlineatus; however, the role that T plays in the performance of A. sexlineatus or other mate guarding species remains unknown. For this study, male racerunners were captured and blood samples were drawn immediately to quantify T levels. Lizards were then returned to the lab where locomotor performance (endurance), bite force, and morphological data were collected. Following performance trials, lizards received silastic T implants. Lizards were housed in the lab for four weeks where locomotor endurance and bite force performance were measured biweekly. Additionally, a blood sample was collected every two weeks to monitor T levels. This research will quantify the morphological and physiological factors affecting performance in A. sexlineatus and provide valuable data concerning how T affects alternative mating systems.


Society for Integrative and Comparative Biology Annual Meeting (SICB)


Boston, MA