Fig. 1. Continuous measurements of oxygen consumption (V._O2) and carbon dioxide production (V._CO2) in one representative embryo from 12 h before to 12 h after hatching. The embryo was at the incubation temperature of 38 °C. EP indicates the onset of external pipping, with star fracture of the shell. Interruptions in the continuous lines indicate that the sampling was temporarily halted to check for baseline.

Fig. 2. Left panel: oxygen consumption (V._O2) measured continuously during the last 30 min at 38 °C, and one hour at 30 °C, in embryos at different times of the hatching process, and in hatchlings. The vertical dashed line indicates the onset of the 30 °C exposure. Right panel: the V._O2 data in the cold are plotted as percent of the 38 °C value preceding the onset of the cold (100%, horizontal dashed line). The fainter symbols refer to embryos studied at day 11 (E11), at which time they are strictly ectothermic, and the continuous line is the linear regression through the E11 data points. Symbols are mean values of 7 to 17 animals (or 5 sets of 2 embryos each in the case of E11). Bars indicate 1 SEM. Curves with different letters are statistically different from each other.

Fig. 3. Weight of eggs maintained at a constant temperature in a desiccator for various days. Open symbols refer to intact eggs, filled symbols refer to eggs with the eggshell removed at its blunted end, for an area of about 1 cm². The heavy and dashed lines are the linear regressions through the mean values of the intact and opened eggs, respectively.

Fig. 4. Oxygen consumption (V._O2) in warm conditions (38 °C) and during the 60 min of cold exposure (30 °C) in embryos during the internal pipping (IP) phase. At left are Controls (N = 7), run 1 and run 2 referring to the two consecutive thermogenic responses. At right are experimental embryos (N = 10), in the intact situation (open symbols), and with the eggshell opened (filled symbols). The bottom panels represent the thermogenic responses, where the values in the cold are expressed as percent of the warm values. The continuous oblique line represents the response of the purely ectothermic embryos, at day E11 (from Fig. 2). Symbols are group means, bars indicate 1 SEM.

Fig. 5. Oxygen consumption (V._O2) in warm conditions (38 °C) and during the 60 min of cold exposure (30 °C) in embryos during the star fracture of the external-pipping (EP) phase. At left are Controls (N = 7), run 1 and run 2 referring to the two consecutive thermogenic responses. At right are represented the embryos of the experimental group, in the intact situation (open symbols), and with the eggshell removed from the blunted end of the egg (filled symbols). The bottom panels represent the thermogenic responses, where the values in the cold are expressed as percent of the warm values. The continuous oblique line represents the response of the purely ectothermic embryos, at day E11 (from Fig. 2). Symbols are group means, bars indicate 1 SEM.

Fig. 6. Oxygen consumption (V._O2) in warm conditions (38 °C) and during the 60 min of cold exposure (30 °C) in embryos during the star fracture of the external-pipping (EP) phase. Open symbols refer to the intact situation, filled symbols refer to the test with the eggshell removed at the blunted end of the egg and additional O₂ (about 35% O₂). Values are expressed in ml/min (top panel) and in percent of the values attained at 38 °C (bottom panel). Symbols are group means (N = 10), bars indicate 1 SEM.

Fig. 7. Thermogenic response in embryos incubated at 35 °C during the last three days of incubation. All embryos were studied during the star fracture of the external-pipping (EP) phase. At top, oxygen consumption (V._O2) is expressed in absolute values (ml/min) during warm conditions (38 °C) and during the 1-hour cold exposure (30 °C). At bottom, values of V._O2 are expressed in percent of those at 38 °C. Open and filled symbols, refer, respectively, to the condition of intact eggshell and of eggshell removed at the blunted end of the egg. The continuous oblique line represents the response of the purely ectothermic embryos, at day E11 (from Fig. 2). Symbols indicate group means, bars indicate 1 SEM.

Number of animals, egg weight, age and body weight

Values are mean ± 1 SEM. N, number of animals.