We have shown that in response to mild hypoxia or
hyperoxia, the internally pipped embryo maintains V · O2total.
During acute exposure to most of the treatments, a decrease in
V ·
O2 at one site was compensated with a similar increase inV ·
O2 at
the other site. Under hypoxic conditions, this is accomplished
by a tradeoff in V ·
O2lung and V ·
O2CAM such that V ·
O2 at the site
exposed to hypoxia decreases andV ·
O2 at the other site increases.
The ability of the embryo to defend V ·
O2total is lost when both
sites are exposed to mild hypoxia. This hypometabolism has
also been observed in externally pipped embryos in response to
hypoxia (Tazawa et al., 1992; Mortola and Labbè, 2005).
Additionally, hyperoxic conditions (40% O2) resulted in an 8%
and 15% increase in V ·
O2total in day 18 and externally pipped
embryos (Tazawa et al., 1992).