Alternating egg-brooding behaviors create and modulate a hypoxic developmental micro-environment in Children's pythons (Antaresia childreni)

Parental care is a widespread and ecologically relevant adaptation known to enhance the developmental environment of offspring. Parental behaviors, however, may entail both costs and benefits for developing offspring. In Children's pythons (Antaresia childreni), we monitored both maternal egg-brooding behavior and intra-clutch oxygen partial pressure (PO2) in real-time to assess the effects of various brooding behaviors on PO2 in the clutch micro-environment at three stages of development. Furthermore, at the same developmental stages, we measured O2 consumption rates (VO2) of eggs at varying PO2 to determine their critical oxygen tension (i.e. the minimal PO2 that supports normal respiratory gas exchange) and to predict the impact that naturally brooded intra-clutch PO2 has on embryonic metabolism. At all three stages of development, a tightly coiled brooding posture created an intra-clutch PO2 that was significantly lower than the surrounding nest environment. Maternal postural adjustments alleviated this hypoxia, and the magnitude of such corrections increased with developmental stage. Mean intra-clutch PO2 decreased with stage of development, probably because of increasing egg VO2. Additionally, embryo critical oxygen tension increased with developmental stage. Together, these results suggest that python embryos are unable to maintain normal metabolism under brooded conditions during the final 10% of incubation. These results demonstrate that specific parental behaviors can impose obligatory costs to developing offspring and that balancing these behaviors can mediate deleterious consequences.