Influence of incubation water content on oxygen uptake in embryos of the Burmese python (Python molurus bioittatus)

Abstract

Flexible-shelled reptilian eggs exchange water via two routes; 1) diffusive water vapor loss through shell interstices and 2) liquid water imbibition from incubation substrate in response to a water potential gradient. Uptake of liquid water may result in the filling of some of the shell interstices which would in turn increase shell O₂ diffusion resistance. We measured whole-egg mass changes, water vapor conductance (${G_{{H_2}O}}$), O₂ consumption, trans-shell ${P_{{O_2}}}$ gradient, incubation period, and hatchling weights in four groups of Burmese python (Python molurus bivittatus) eggs incubated in substrates with estimated water potentials of −360, −220, −130 and −80 kPa respectively. O₂ consumption among the four groups did not differ significantly throughout incubation. Trans-shell ${P_{{O_2}}}$ gradients measured during the periods of maximum O₂ consumption varied from 34 ± 6 (s.e.) torr in eggs incubated in the driest substrate to 64 ± 9 torr in eggs incubated in the wettest substrate, and O₂ conductance values calculated from trans-shell ${P_{{O_2}}}$ and O₂ consumption data were only about one-tenth of that predicted from ${G_{{H_2}O}}$. Thus, the incubating Burmese python egg has a functional water layer in the shell, and the embryos are subject to hypoxia comparable to that observed in developing chicken embryos. This does not appear to compromise tissue O₂ delivery, however, because hatchling weights and O₂ consumption are not adversely affected by increased incubation substrate water content.