BRANDT, Y*; CHAPPELL, MA; University of Toronto at Scarborough; University of California, Riverside: Do threat displays in lizards handicap endurance by interfering with respiration?

Threat displays, the signals employed in agonistic interactions, appear to advertise aggression and fighting prowess. Handicaps, signals whose honesty is maintained by the cost of signal production, are seldom employed as threat displays. However, in lizards, individual variation in the duration of threat posturing correlates with endurance (duration of exercise at a standard intensity of) – a predictor of dominance. Furthermore, threat displays are followed by elevated lactate concentrations and impaired endurance capacity, and thus appear to function as handicaps. Threat posturing appears to abolish ventilatory movements of the ribcage, therefore we hypothesized that threat posturing impairs endurance by interfering with ventilation. We used flow-through CO2 respirometry to examine the effect of threat posturing on respiration rates of Side-blotched lizards Uta stansburiana and Western fence lizards Sceloporus occidentalis. At the onset of each bout of threat posturing, respiration rates declined close to zero, increasing only after the threat posture was relaxed. This pattern contrasted with the increased respiration rates recorded during the production of push-up displays and during bouts of locomotion. These results are consistent with the prediction that threat posturing interferes with respiration. To test whether respiratory interference can impair endurance we measured the impact of exposure to hypoxic gas (10% oxygen, 90% nitrogen, for one minute or for five minutes) on subsequent endurance capacity. Contrary to our expectations, endurance capacity was not affected by prior exposure to hypoxia. We suggest that although threat posturing both interferes with respiration and impairs endurance, the impairment of endurance may not be caused directly by reducing pulmonary oxygen concentrations.