ENERGETICS OF DEVELOPMENT OF EMBRYOS OF THE AUSTRALIAN FRESH-WATER CROCODILE, CROCODYLUS-JOHNSTONI - RELATION TO DURATION OF INCUBATION

At laying, eggs of Crocodylus johnstoni contain approximately 440 kJ of energy. During constant-temperature incubation this energy is depleted from the egg at 1.47 times the rate of accumulation in embryonic tissue. Thus, energetic efficiency during development is 68%. Additional losses in membranes and other residues at hatching (16 kJ) reduce whole-incubation efficiency to about 65%. Energy losses are similar at 29-degrees and 31-degrees-C, despite a 19-d (24%) extension of the incubation period at the lower temperature. Total production efficiency in C. johnstoni is similar to other reptiles but higher than in birds. We suggest that energy costs of development of reptilian embryos are relatively insensitive to duration of incubation because maintenance costs are small compared with other energy demands.