Oxygen Consumption and Growth of Northern Bobwhite Embryos under Normoxic and Hyperoxic Conditions

Abstract

The oxygen limitation hypothesis states that during the latter stages of incubation O2 availability limits growth and metabolism of embryos of precocial birds. The hypothesis has received support when tested on chicken embryos (Gallus gallus); we have attempted to extend the hypothesis to another precocial species, the Northern Bobwhite (Colinus virginianus). Quail embryos rapidly increased in mass until late in the incubation period when the growth rate declined. This pattern is typical of embryos of other similar-sized precocial birds. Data for the metabolic rate of quail embryos incubated in air (normoxia, 21% O2 paralleled data for embryo mass with the preIP V̇O2 averaging 4.73 ± 0.81 ml/hr. To test whether elevated levels of O2 affected the growth rate of quail embryos, we switched the gas that eggs were receiving from normoxic to hyperoxic (60% O) on day 11. Wet mass of embryos from hyperoxic eggs did not differ from that of control embryos on days 12, 14, 16, 18, and 20 of incubation. The metabolic rate of embryos incubated under hyperoxic conditions for 24 hr (days 14-15) or for 6 days (days 14-20) did not vary from controls. Moreover, the metabolic rate of normoxic eggs (days 17 and 18) did not increase when we exposed the air cell to ambient air. Thus we were unable to support the oxygen limitation hypothesis when tested on Northern Bobwhite embryos.