ZANI, Peter A.*; JONES, Trevor D.; Central College: Effect of reproductive burden on endurance in side-blotched lizards

In most taxa studied to date, reproductive burden has been reported to reduce locomotor performance. However, many of these studies classified subjects as simply either gravid or non-gravid, and did not consider the different stages of reproduction. By conducting a mark-recapture study of side-blotched lizards (Uta stansburiana) in eastern Oregon, we were able to collect females with no follicles, enlarged follicles, yolked eggs, or shelled eggs. Endurance trials (time to exhaustion) were performed using a motorized treadmill moving at 0.2 m/s. During May and June of 2005, endurance trials were performed on 169 females. After the effects of body length were taken into account using statistical residuals, endurance times of non-gravid females (raw mean � 1 S.E.M.: 216 � 8.7 s; n = 45) were statistically indistinguishable (P > 0.05) from reproductive females with enlarged follicles (219 � 12.5 s; n = 49) as well as females with yolked eggs (205 � 11.9 s; n = 25). However, non-gravid females had significantly greater endurance than females with shelled eggs (196 � 12.7 s; n = 25; F = 4.0; P = 0.04). This corresponds to a 9.3 % reduction in endurance capacity. Thus, the trend toward increasing reproductive burden does not significantly impair locomotor performance until just prior to oviposition. In the lab, we also measured endurance within 24-48 h of oviposition. Post-reproductive females (225 � 19.2 s; n = 25) recovered their endurance capacity to levels indistinguishable from non-reproductive females very rapidly, suggesting that the major burden of reproduction is biomechanical. Assuming decreased endurance increases the risk of mortality in the wild, the major risk of mortality associated with reproductive burden should occur very transiently just prior to egg laying.