LIGON, D.B.; Oklahoma State University: Effects of Incubation Temperature on Embryonic Development In a Tortoise, Geochelone sulcata

The thermal environment to which reptile embryos are exposed can vary both temporally and spatially among individuals. In response to variable incubation conditions, developing embryos may make physiological adjustments to compensate for temperature differences. Physiological compensation in response to chronic acclimation reduces the acute physiological effects of temperature. However, among reptiles the degree of compensation exhibited in growth and resting metabolic rate (RMR; oxygen consumption) in response to incubation temperature (T_inc) varies across taxa. For example, the duration of the incubation period is consistently inversely correlated with T_inc, but peak oxygen consumption is positively correlated with T_inc in some species and not others. This suggests that some reptile embryos experience �perfect� metabolic compensation during the late stages of development, whereas others do not. I tested the effects of T_inc on the pattern of oxygen consumption in African spurred tortoise (Geochelone sulcata) embryos. Eggs were collected from six nests produced in captivity, and incubated at five constant temperatures spaced at 1° C intervals (range = 28.5°-32.5°C) on vermiculite maintained at approximately �150 kPa. Measurements to determine the effects of incubation temperature on embryonic growth and RMR were collected at 10-d intervals beginning 10 d after oviposition. Incubation temperature affected the pattern of oxygen consumption, but differences in peak RMR only existed across T_inc intervals >4° C, indicating that partial metabolic compensation occurred across the range of temperatures studied.