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Oxygen consumption of eggs and hatchlings of the Nile crocodile (Crocodylus niloticus)
Vol. Il2A, No. I, pp.W-102, Copyright 0 1995Elsevier Science
Camp. Biochem. Physiol.
Pergamon
Printed
in Great
Britain.
All
0300-9629/95
0300-9629(95)000&M
rights
1995 Ltd
reserved
$9.50 + 0.00
Oxygen consumption of eggs and hatchlings of the Nile crocodile (Crocodylus niloticus) Arnfinn Aulie* and Toitus I. Kanui”f *Department of Biochemistry, Physiology and Nutrition, Norwegian College of Veterinary Medicine, P.O. Box 8146 Dep., N-0033 Oslo, Norway; and TDepartment of Animal Physiology, College of Agriculture and Veterinary Sciences, University of Nairobi, P.O. Box 30197 Nairobi, Kenya PO, of Nile crocodile embryos was measured at 32°C during the last half of the incubation period and for 10 days after hatching. Peak BO, occurred when incubation was 87% completed. Thereafter, PO, decreased until hatching, following the same peaked pattern as in embryos of other crocodilians. After hatching, VO, increased to 119% of peak PO,, indicating a higher gas exchange capacity during pulmonary respiration than during chorioallantoic respiration. Key words: Nile crocodile; Crocodylus niloticus; Embryos; Hatchlings; Metabolism; Peaked pattern. Comp. Biochem. Physiol. 112A, 99-102,
1995
Introduction During the last part of the incubation period, some reptilian embryos show a marked fall in their oxygen consumption (li0,). The peak occurs at about 88% of the way through incubation in all of the crocodilians Alligator mississipiensis (Thompson, 1989), Crocodylus johnstoni and Crocodylus porosus (Whitehead and Seymour, 1990). The oxygen consumption did not change the first day after hatching in A. mississipiensis and C. johnstoni (Thompson, 1989; Whitehead and Seymour, 1990), while it increased in the hatchlings of Crocodylus niloticus (Aulie et al., 1989). This indicates that the embryos of C. niloticus, as chicken embryos (Metcalfe et al., 1984), may have outgrown the 0, diffusing capacity of their gas exchange systems during late incubation. If so, one would expect the ontogeny of embryonic VO, in the Nile crocodile to be sigmoid rather than peaked. Previous VOz measurements on eggs from C. niloticus were too few to tell which pattern they
followed (Aulie et al., 1989). The main objective of the present study was therefore to describe the pattern of PO2 of Nile crocodiles embryos. PO, was measured during the last half part of the incubation period and for 10 days after hatching.
Materials and Methods Ten eggs of the Nile crocodile, which had been incubated for 50 days at approximately 31°C at a crocodile farm in Mombasa, Kenya, were transported to the Norwegian College of Veterinary Medicine, Norway. During the 2day-transport, the eggs were kept at room temperature (22-28”(Z). On arrival, the mean weight of the eggs was 83.5 + 2.9 g. The eggs were buried in a 67 cm thick layer of moist vermiculite in a chicken incubator (Glarus 8750), and the incubation was continued at 31.0 + 0S”C. All the eggs hatched between 99 and 100 days after laying. The mean weight of the hatchlings was 55.2 + 2.4 g. They were transferred to an 80 1 aquarium containing sand, flat stones and 10 1 of tap water. The water temperature was kept at 30.0 + l.o”C by adjusting the height of a 250 W infra-red lamp hanging above the aquarium. The hatchlings were not fed during
to: Amfinn Aulie, Department of Biochemistry, Physiology and Nutrition, Norwegian College of Veterinary Medicine, P.O. Box 8146 Dep., N-0033 Oslo, Norway. Tel. 47 22 96 45 84; Fax 47 22 60 09 85. Received 13 February 1994; revised 3 March 1995; accepted 14 March 1995. Correspondence
99
100
A. Aulie
and T. I. Kanui
the experiment. Afterwards, they were fed, and all the hatchlings survived for at least 2 months. The oxygen uptakes of the eggs and hatchlings were measured at 32.0 + O.l”C in a constant pressure differential manometric respirometer placed in a thermoregulated water bath. The measuring device consisted of an air-tight respiratory chamber (0.5 1) connected to a similar compensatory chamber through an M-shaped tube. The tube was partly filled with coloured soap water. During the egg experiments, about 40g of soda lime was placed at the bottom of the respiratory chamber and the egg placed on a screen above the absorber. During experiments on hatchlings, the absorber was kept in two perforated plastic tubes fastened to the lid. When 0, was consumed and CO, absorbed, the pressure in the respiratory chamber decreased. By injecting pure O2 into the respiratory chamber by means of a 2 ml air-tight precision syringe, the pressure difference between the two chambers was abolished. 30, was calculated by taking the exact time for the consumption of 1 ml Oz. All rate values were adjusted to 0°C and 760 mmHg. The egg or the hatchling was prewarmed to 32°C for at least 2 hr before it was placed in the spirometer. The oxygen uptake was measured until stable values were obtained; thereafter at least four measurements were made and the mean value used. 30, of each egg was measured once a week, and four to five eggs were measured per day. Thus, 2-3 days elapsed between the first and the last measurement. The prehatch vOz was measured in seven eggs which had not pipped or hatched on day 99. Values are expressed as mean + standard deviation of mean. Statistical comparisons were made by means of Student’s r-test, and P values ~0.05 were accepted as indicating significant differences.
30, of the 5-10 days old hatchlings was 10.39 f 1.04 ml/hr (N = S), which is significantly higher than the peak consumption (P < 0.002). A few measurements on 16-21 day old hatchlings after feeding started, indicated that 302 (IO.71 f 3.14 ml/hr, N = 3) did not increase above the day- 10 level.
Discussion The metabolic rate of the developing Nile crocodile followed the same peaked pattern as embryos from other reptiles that develop in hard-shelled eggs. The peak occurred 87% of the way through incubation, which is about the same as that found in embryos from both Crocodylus johnstoni and Crocodylus porosus (Whitehead and Seymour, 1990) and in All&atar mississipiensis (Thompson, 1989). The maximal specific PO, of C. johnstoni was 91 pl/hr . g (egg) at 29”C, while the C. niloticus eggs with similar weight consumed 105 pl/hr . g (egg) at 32°C. With a temperature coefficient (Qlo) of 1.8 between 25 and 32°C (Aulie et al., 1989), one would expect the PO2 of the C. niloticus to be 88 pl/hr . g at 29”C, or about the same as for C. johnstoni. The larger eggs from C. porosus (107 g) had a peak VO, of 110 pl/hr . g (egg) at 30°C. This is 18% higher than one would expect the value from C. niloticus to be at 30°C. Direct comparison with the peak consumption of embryos of A. mississipiensis reported by Thompson (1989) cannot be done due to a missing egg weight. However, assuming a mean weight of 84 g (Ferguson, 1985), the maximum specific li0, seems to be the same as for C. porosus.
12 r
Results The mean $‘O, increased approximately linearly during the first part of the measuring period (53-80 days). During the following 2 weeks, it was stable before it decreased the last week before hatching. The oxygen consumption increased during the first IO days after hatching (Fig. 1). The mean peak 30, was 8.76 + 0.69ml/hr (N = 10) and was reached in. 86.9 + 2.9 days (range 80-94). The prehatch VO, measured on day 99 was 7.23 + 0.57 ml/hr (N = 7) and significantly lower (P < 0.002) than the peak consumption. The PO, of the O-3 day old hatchlings was 8.75 & 0.97 ml/hr (N = 7) and significantly higher than prehatch VO, (P < 0.005). The
50
60
70
80
90
100
HO
Ageidoys)
Fig. I. Oxygen consumption of eggs and hatchlings of Nile crocodile at different ages. The ambient temperature was 32°C. Each point is the mean of seven to ten measurements from different eggs or hatchlings and the vertical bars one SD about the mean. The arrow indicates the start of hatching.
FO, of Nile crocodile eggs and hatchlings
Both A. mississipiensis and C. porosus construct mounds of vegetation in which the eggs are deposited (Thompson, 1989) while C. johnstoni and C. niloticus construct a hole-nest in dry soil or sand. In the domestic fowl eggs, the maximum PO, depends on the porosity of the egg shell, and eggs with a high water vapour conductance (GH,O) consume more oxygen in the plateau phase than eggs with a low conductance (Tullett and Deeming, 1982). In Brush-turkey eggs, which are incubated in a mound-nest, GH,O is 2.6 times higher than predicted for a typical avian egg of a similar size and incubation period. The high conductance is probably an adaptation to the high humidity and PCO, and low PO, in the nest (Seymour and Rahn, 1978). Although GH,O values of fertile eggs from the moundnesters A. mississipiensis and C. porosus are 4.2 and 3.5 times higher than predicted from avian eggs of similar sizes (Packard et al., 1979; Grigg and Beard, 1985) we do not know whether this is an adaptation to the environment in a mound-nest or only a reflection of the high GH,O of fertile crocodilian eggs. Prior to hatching, the VO, of the Nile crocodile embryos decreased to 83% of the peak value, which is about the same as that found in the other crocodilians (Thompson, 1989; Whitehead and Seymour, 1990). The reduction in ri0, seems to be associated with a declining growth rate of the embryos (Whitehead and Seymour, 1990). According to Thompson (1989) this may be a way to secure hatching synchrony in a single clutch where different eggs experience different temperature regimes and thereby develop at different rates. The fact that the time of peak VO, varied from 80 to 94 days in the present study indicates that the development times also differ within eggs incubated at the same temperature. After hatching, the oxygen uptake of the Nile crocodile increased, which is in agreement with a previous study on the same species (Aulie et al., 1989). The consumption of the 0-3-dayold hatchlings was 21% higher than the prehatch value, while that of the 5-lo-day-old hatchlings was as much as 44% higher. Thompson (1989) observed a 10% increase after pipping in turtle eggs (Emydura macquarii ), while there seemed to be no increase in A. mississipiensis and C. johnstoni the first day after hatching (Thompson, 1989; Whitehead and Seymour, 1990). Nile crocodile eggs incubated at 37°C increased VO, by 29% when they were exposed to pure oxygen during the part of the incubation where peak ri0, occurred in the present study. Breathing pure oxygen after hatching had no effect on the uptake (Aulie et al., 1989). Since the crocodile embryo increases its oxygen up-
101
take during incubation at high external PO,, the gas exchange may, as in birds (Hsiby et al., 1983), be restricted during incubation in air at 37°C. An eventually restricted gas exchange at peak V02 during incubation in air at 32°C should have a minor impact on the development of the embryo since the growth rate of the crocodilian embryo declines during the last stage of incubation (Whitehead and Seymour, 1990). Most bird embryos pip internally and there is a gradual switchover from diffusive gas exchange through chorioallantois to active breathing through the lungs. During this period, PO, increases (Rahn et al., 1979). Crocodile embryos do not pip internally and the switch to pulmonary respiration does not occur until the egg shell is pipped (Booth and Thompson, 1991). The resting VO, of the Nile crocodile reached only peak values the first days after hatching. After a week, it was 19% above peak PO,. It seems, therefore, that the lung and/or the cardiovascular system of the hatchling take some time to maturate after hatching. When the temperature was increased from 32 to 37°C the effect on ri0, was much larger for the hatchlings (Q10= 2.6) than for the embryos (Q10= 1.3) (Aulie et al., 1989). This indicates that the Nile crocodile has a higher gas exchange capacity during pulmonary respiration than during chorioallantoic respiration. This study has shown that the Nile crocodile follows the same peaked LO, pattern as other crocodilian embryos during incubation. work was supported by a grant from the NORAD KEN 046 Project. The authors express their gratitude to Dr Oivind Toien for reading the manuscript. Acknowledgements-This
References Aulie A., Kanui T. I. and Maloiy G. M. 0. (1989) The effects of temperature on oxygen consumption of eggs and hatchlings of the Nile crocodile (Crocodylus niloticus). Comp. Biochem. Physiol. 93A, 473415.
Booth D. T. and Thompson M. B. (1991) A comparison of reptilian eggs with those of megapode birds. In Egg Incubation (Edited by Deeming D. C. and Ferguson M. W. J.), pp. 325-344. Cambridge University Press, Cambridge. Ferguson M. W. J. (1985) Reproductive biology and embryology of the crocodilians. In Biology of the Reptilia, Vo1?14, Development A (Edited by Gans C!., Billett F. and Maderson P. F. A.), pp. 329-491. John Wiley, New York. Grigg G. and Beard L. (1985) Water loss and gain by eggs of Crocodylus porosus, related to incubation age gnd fertility. In Biology of Australasian Frogs and Reptiles (Edited by Grigg G., Shine R. and Ehmann H.), pp. 353-359. Surrey Beatty Pty Ltd, Sydney. Hobby M., Aulie A. and Reite 0. B. (1983) Oxygen uptake in fowl eggs incubated in air and in pure oxygen. Comp. Biochem. Physiol. 74A, 3 15-3 18. Metcalfe J., Stock M. K. and Ingermann R. L. (1984) The
102
A. Aulie and T. I. Kanui
effect of oxygen and development of the chick .- on growth embryo. In Respiration and Metabolism of Embryonic Vertebrates (Edited bv Seymour R. S.), PP. 205-219. Junk, Dordrkcht, The Netherlands. __ Packard Cl. C., Taigen T. L., Packard M. J. and Shuman R. D. (1979) Water-vapour conductance of testudinian and crocodilian eggs (Class Reptilia). Respir. Physiol. 38, I-10. Rahn H., Ar A. and Paganelli C. V. (1979) How bird eggs breathe. Sci. Am. 240, 38-47. Seymour R. S. and Rahn H. (1978) Gas conductance in the eggshell of the mound-building Brush turkey. In Respir-
ation Function in Birds, Adult and Embryonic (Edited by Piiper J.), pp. 242-246. Springer, Berlin. Thompson M. B. (1989) Patterns of metabolism in embryonic reptiles. Reipir. Physiol. 76, 234-256. Tullett S. G. and Deemine D. C. (1982) The relationshin between eggshell porosit; and oxygen consumption of the embryo in the domestic fowl. Comp. Biochem. Physiol. 72A, 529-533. Whitehead P. J. and Seymour R. S. (1990) Patterns of metabolic rate in embryonic crocodilians Crocodylus johnstoni and Crocodylus porosus. Physiol. Zool. 63, 334-352.
Camp. Biochem. Physiol.
Pergamon
Printed
in Great
Britain.
All
0300-9629/95
0300-9629(95)000&M
rights
1995 Ltd
reserved
$9.50 + 0.00
Oxygen consumption of eggs and hatchlings of the Nile crocodile (Crocodylus niloticus) Arnfinn Aulie* and Toitus I. Kanui”f *Department of Biochemistry, Physiology and Nutrition, Norwegian College of Veterinary Medicine, P.O. Box 8146 Dep., N-0033 Oslo, Norway; and TDepartment of Animal Physiology, College of Agriculture and Veterinary Sciences, University of Nairobi, P.O. Box 30197 Nairobi, Kenya PO, of Nile crocodile embryos was measured at 32°C during the last half of the incubation period and for 10 days after hatching. Peak BO, occurred when incubation was 87% completed. Thereafter, PO, decreased until hatching, following the same peaked pattern as in embryos of other crocodilians. After hatching, VO, increased to 119% of peak PO,, indicating a higher gas exchange capacity during pulmonary respiration than during chorioallantoic respiration. Key words: Nile crocodile; Crocodylus niloticus; Embryos; Hatchlings; Metabolism; Peaked pattern. Comp. Biochem. Physiol. 112A, 99-102,
1995
Introduction During the last part of the incubation period, some reptilian embryos show a marked fall in their oxygen consumption (li0,). The peak occurs at about 88% of the way through incubation in all of the crocodilians Alligator mississipiensis (Thompson, 1989), Crocodylus johnstoni and Crocodylus porosus (Whitehead and Seymour, 1990). The oxygen consumption did not change the first day after hatching in A. mississipiensis and C. johnstoni (Thompson, 1989; Whitehead and Seymour, 1990), while it increased in the hatchlings of Crocodylus niloticus (Aulie et al., 1989). This indicates that the embryos of C. niloticus, as chicken embryos (Metcalfe et al., 1984), may have outgrown the 0, diffusing capacity of their gas exchange systems during late incubation. If so, one would expect the ontogeny of embryonic VO, in the Nile crocodile to be sigmoid rather than peaked. Previous VOz measurements on eggs from C. niloticus were too few to tell which pattern they
followed (Aulie et al., 1989). The main objective of the present study was therefore to describe the pattern of PO2 of Nile crocodiles embryos. PO, was measured during the last half part of the incubation period and for 10 days after hatching.
Materials and Methods Ten eggs of the Nile crocodile, which had been incubated for 50 days at approximately 31°C at a crocodile farm in Mombasa, Kenya, were transported to the Norwegian College of Veterinary Medicine, Norway. During the 2day-transport, the eggs were kept at room temperature (22-28”(Z). On arrival, the mean weight of the eggs was 83.5 + 2.9 g. The eggs were buried in a 67 cm thick layer of moist vermiculite in a chicken incubator (Glarus 8750), and the incubation was continued at 31.0 + 0S”C. All the eggs hatched between 99 and 100 days after laying. The mean weight of the hatchlings was 55.2 + 2.4 g. They were transferred to an 80 1 aquarium containing sand, flat stones and 10 1 of tap water. The water temperature was kept at 30.0 + l.o”C by adjusting the height of a 250 W infra-red lamp hanging above the aquarium. The hatchlings were not fed during
to: Amfinn Aulie, Department of Biochemistry, Physiology and Nutrition, Norwegian College of Veterinary Medicine, P.O. Box 8146 Dep., N-0033 Oslo, Norway. Tel. 47 22 96 45 84; Fax 47 22 60 09 85. Received 13 February 1994; revised 3 March 1995; accepted 14 March 1995. Correspondence
99
100
A. Aulie
and T. I. Kanui
the experiment. Afterwards, they were fed, and all the hatchlings survived for at least 2 months. The oxygen uptakes of the eggs and hatchlings were measured at 32.0 + O.l”C in a constant pressure differential manometric respirometer placed in a thermoregulated water bath. The measuring device consisted of an air-tight respiratory chamber (0.5 1) connected to a similar compensatory chamber through an M-shaped tube. The tube was partly filled with coloured soap water. During the egg experiments, about 40g of soda lime was placed at the bottom of the respiratory chamber and the egg placed on a screen above the absorber. During experiments on hatchlings, the absorber was kept in two perforated plastic tubes fastened to the lid. When 0, was consumed and CO, absorbed, the pressure in the respiratory chamber decreased. By injecting pure O2 into the respiratory chamber by means of a 2 ml air-tight precision syringe, the pressure difference between the two chambers was abolished. 30, was calculated by taking the exact time for the consumption of 1 ml Oz. All rate values were adjusted to 0°C and 760 mmHg. The egg or the hatchling was prewarmed to 32°C for at least 2 hr before it was placed in the spirometer. The oxygen uptake was measured until stable values were obtained; thereafter at least four measurements were made and the mean value used. 30, of each egg was measured once a week, and four to five eggs were measured per day. Thus, 2-3 days elapsed between the first and the last measurement. The prehatch vOz was measured in seven eggs which had not pipped or hatched on day 99. Values are expressed as mean + standard deviation of mean. Statistical comparisons were made by means of Student’s r-test, and P values ~0.05 were accepted as indicating significant differences.
30, of the 5-10 days old hatchlings was 10.39 f 1.04 ml/hr (N = S), which is significantly higher than the peak consumption (P < 0.002). A few measurements on 16-21 day old hatchlings after feeding started, indicated that 302 (IO.71 f 3.14 ml/hr, N = 3) did not increase above the day- 10 level.
Discussion The metabolic rate of the developing Nile crocodile followed the same peaked pattern as embryos from other reptiles that develop in hard-shelled eggs. The peak occurred 87% of the way through incubation, which is about the same as that found in embryos from both Crocodylus johnstoni and Crocodylus porosus (Whitehead and Seymour, 1990) and in All&atar mississipiensis (Thompson, 1989). The maximal specific PO, of C. johnstoni was 91 pl/hr . g (egg) at 29”C, while the C. niloticus eggs with similar weight consumed 105 pl/hr . g (egg) at 32°C. With a temperature coefficient (Qlo) of 1.8 between 25 and 32°C (Aulie et al., 1989), one would expect the PO2 of the C. niloticus to be 88 pl/hr . g at 29”C, or about the same as for C. johnstoni. The larger eggs from C. porosus (107 g) had a peak VO, of 110 pl/hr . g (egg) at 30°C. This is 18% higher than one would expect the value from C. niloticus to be at 30°C. Direct comparison with the peak consumption of embryos of A. mississipiensis reported by Thompson (1989) cannot be done due to a missing egg weight. However, assuming a mean weight of 84 g (Ferguson, 1985), the maximum specific li0, seems to be the same as for C. porosus.
12 r
Results The mean $‘O, increased approximately linearly during the first part of the measuring period (53-80 days). During the following 2 weeks, it was stable before it decreased the last week before hatching. The oxygen consumption increased during the first IO days after hatching (Fig. 1). The mean peak 30, was 8.76 + 0.69ml/hr (N = 10) and was reached in. 86.9 + 2.9 days (range 80-94). The prehatch VO, measured on day 99 was 7.23 + 0.57 ml/hr (N = 7) and significantly lower (P < 0.002) than the peak consumption. The PO, of the O-3 day old hatchlings was 8.75 & 0.97 ml/hr (N = 7) and significantly higher than prehatch VO, (P < 0.005). The
50
60
70
80
90
100
HO
Ageidoys)
Fig. I. Oxygen consumption of eggs and hatchlings of Nile crocodile at different ages. The ambient temperature was 32°C. Each point is the mean of seven to ten measurements from different eggs or hatchlings and the vertical bars one SD about the mean. The arrow indicates the start of hatching.
FO, of Nile crocodile eggs and hatchlings
Both A. mississipiensis and C. porosus construct mounds of vegetation in which the eggs are deposited (Thompson, 1989) while C. johnstoni and C. niloticus construct a hole-nest in dry soil or sand. In the domestic fowl eggs, the maximum PO, depends on the porosity of the egg shell, and eggs with a high water vapour conductance (GH,O) consume more oxygen in the plateau phase than eggs with a low conductance (Tullett and Deeming, 1982). In Brush-turkey eggs, which are incubated in a mound-nest, GH,O is 2.6 times higher than predicted for a typical avian egg of a similar size and incubation period. The high conductance is probably an adaptation to the high humidity and PCO, and low PO, in the nest (Seymour and Rahn, 1978). Although GH,O values of fertile eggs from the moundnesters A. mississipiensis and C. porosus are 4.2 and 3.5 times higher than predicted from avian eggs of similar sizes (Packard et al., 1979; Grigg and Beard, 1985) we do not know whether this is an adaptation to the environment in a mound-nest or only a reflection of the high GH,O of fertile crocodilian eggs. Prior to hatching, the VO, of the Nile crocodile embryos decreased to 83% of the peak value, which is about the same as that found in the other crocodilians (Thompson, 1989; Whitehead and Seymour, 1990). The reduction in ri0, seems to be associated with a declining growth rate of the embryos (Whitehead and Seymour, 1990). According to Thompson (1989) this may be a way to secure hatching synchrony in a single clutch where different eggs experience different temperature regimes and thereby develop at different rates. The fact that the time of peak VO, varied from 80 to 94 days in the present study indicates that the development times also differ within eggs incubated at the same temperature. After hatching, the oxygen uptake of the Nile crocodile increased, which is in agreement with a previous study on the same species (Aulie et al., 1989). The consumption of the 0-3-dayold hatchlings was 21% higher than the prehatch value, while that of the 5-lo-day-old hatchlings was as much as 44% higher. Thompson (1989) observed a 10% increase after pipping in turtle eggs (Emydura macquarii ), while there seemed to be no increase in A. mississipiensis and C. johnstoni the first day after hatching (Thompson, 1989; Whitehead and Seymour, 1990). Nile crocodile eggs incubated at 37°C increased VO, by 29% when they were exposed to pure oxygen during the part of the incubation where peak ri0, occurred in the present study. Breathing pure oxygen after hatching had no effect on the uptake (Aulie et al., 1989). Since the crocodile embryo increases its oxygen up-
101
take during incubation at high external PO,, the gas exchange may, as in birds (Hsiby et al., 1983), be restricted during incubation in air at 37°C. An eventually restricted gas exchange at peak V02 during incubation in air at 32°C should have a minor impact on the development of the embryo since the growth rate of the crocodilian embryo declines during the last stage of incubation (Whitehead and Seymour, 1990). Most bird embryos pip internally and there is a gradual switchover from diffusive gas exchange through chorioallantois to active breathing through the lungs. During this period, PO, increases (Rahn et al., 1979). Crocodile embryos do not pip internally and the switch to pulmonary respiration does not occur until the egg shell is pipped (Booth and Thompson, 1991). The resting VO, of the Nile crocodile reached only peak values the first days after hatching. After a week, it was 19% above peak PO,. It seems, therefore, that the lung and/or the cardiovascular system of the hatchling take some time to maturate after hatching. When the temperature was increased from 32 to 37°C the effect on ri0, was much larger for the hatchlings (Q10= 2.6) than for the embryos (Q10= 1.3) (Aulie et al., 1989). This indicates that the Nile crocodile has a higher gas exchange capacity during pulmonary respiration than during chorioallantoic respiration. This study has shown that the Nile crocodile follows the same peaked LO, pattern as other crocodilian embryos during incubation. work was supported by a grant from the NORAD KEN 046 Project. The authors express their gratitude to Dr Oivind Toien for reading the manuscript. Acknowledgements-This
References Aulie A., Kanui T. I. and Maloiy G. M. 0. (1989) The effects of temperature on oxygen consumption of eggs and hatchlings of the Nile crocodile (Crocodylus niloticus). Comp. Biochem. Physiol. 93A, 473415.
Booth D. T. and Thompson M. B. (1991) A comparison of reptilian eggs with those of megapode birds. In Egg Incubation (Edited by Deeming D. C. and Ferguson M. W. J.), pp. 325-344. Cambridge University Press, Cambridge. Ferguson M. W. J. (1985) Reproductive biology and embryology of the crocodilians. In Biology of the Reptilia, Vo1?14, Development A (Edited by Gans C!., Billett F. and Maderson P. F. A.), pp. 329-491. John Wiley, New York. Grigg G. and Beard L. (1985) Water loss and gain by eggs of Crocodylus porosus, related to incubation age gnd fertility. In Biology of Australasian Frogs and Reptiles (Edited by Grigg G., Shine R. and Ehmann H.), pp. 353-359. Surrey Beatty Pty Ltd, Sydney. Hobby M., Aulie A. and Reite 0. B. (1983) Oxygen uptake in fowl eggs incubated in air and in pure oxygen. Comp. Biochem. Physiol. 74A, 3 15-3 18. Metcalfe J., Stock M. K. and Ingermann R. L. (1984) The
102
A. Aulie and T. I. Kanui
effect of oxygen and development of the chick .- on growth embryo. In Respiration and Metabolism of Embryonic Vertebrates (Edited bv Seymour R. S.), PP. 205-219. Junk, Dordrkcht, The Netherlands. __ Packard Cl. C., Taigen T. L., Packard M. J. and Shuman R. D. (1979) Water-vapour conductance of testudinian and crocodilian eggs (Class Reptilia). Respir. Physiol. 38, I-10. Rahn H., Ar A. and Paganelli C. V. (1979) How bird eggs breathe. Sci. Am. 240, 38-47. Seymour R. S. and Rahn H. (1978) Gas conductance in the eggshell of the mound-building Brush turkey. In Respir-
ation Function in Birds, Adult and Embryonic (Edited by Piiper J.), pp. 242-246. Springer, Berlin. Thompson M. B. (1989) Patterns of metabolism in embryonic reptiles. Reipir. Physiol. 76, 234-256. Tullett S. G. and Deemine D. C. (1982) The relationshin between eggshell porosit; and oxygen consumption of the embryo in the domestic fowl. Comp. Biochem. Physiol. 72A, 529-533. Whitehead P. J. and Seymour R. S. (1990) Patterns of metabolic rate in embryonic crocodilians Crocodylus johnstoni and Crocodylus porosus. Physiol. Zool. 63, 334-352.