We measured gas exchange of eggs and mound material as well as gas concentrations at different times during incubation in the mound nests of the salt water crocodile, Crocodylus porosus and the American alligator, Alligator mississippiensis. Oxygen consumption increased gradually during development in both species, peaking well before hatching (at approximately 80% of the incubation period in A. mississippiensis). The RE of eggs at 30 °C and at peak O2 was 0.74 in C. porosus and 0.70 in A. mississippiensis. In a typical mound nest of C. porosus, the oxygen demand of the decomposing nest itself is likely to be 4-7 times that of the clutch at the end of incubation, with a respiratory exchange ratio (RE) of about 0.9. Despite the oxygen demand of nest material, the gaseous environment of the nest is favourable for embryonic development. The lowest pO2 we measured was125 Torr in nests of C. porosus and 133 Torr in nests of A. mississippiensis, with maximum pCO2 of 22 Torr for C. porosus and 23 Torr for A. mississippiensis. Although convective gas exchange might be expected through the nest mound, gas exchange between the clutch and the outside air occurs by diffusion. No unifying theory has yet emerged to provide a satisfactory explanation for the apparently random distribution of hole-nesting and mound-nesting within the Crocodylidae.
Oxygen levels in mound nests of Crocodylus porosus and Alligator mississippiensis are high, and gas exchange occurs primarily by diffusion, not convection
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Gordon Grigg, Michael Thompson, Lyn Beard, Peter Harlow; Oxygen levels in mound nests of Crocodylus porosus and Alligator mississippiensis are high, and gas exchange occurs primarily by diffusion, not convection. Australian Zoologist 1 January 2010; 35 (2): 235–244. doi: https://doi.org/10.7882/AZ.2010.012
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