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.