Oxygen consumption as related to the development of the extraembryonic membranes and cardiovascular system in the European pond turtle (Emys orbicularis) embryogenesis

The rate of oxygen consumption (V˙O2), embryo mass, distribution and mass of the chorioallantoic membrane (CAM), heart rate (HR), heart mass, and amnion rhythmic contractions (ARC) were studied in eggs of the European pond turtle (Emys orbicularis) incubated at 28 °C for 62.5 ± 0.3 days. The V˙O2 rapidly increased beginning from incubation day 19 (D19) to a maximum on D50 and then decreased until pipping. The rapid V˙O2 rise was correlated with an increase in the CAM surface and mass, heart mass, and ARC amplitude, whereas the functional parameters such as HR and ARC frequency remained unchanged. The drop in V˙O2 before pipping was accompanied by a decrease in HR, while the heart and CAM masses were almost constant. In the cases of short-term temperature deviations of ± 3 °C from 28 °C, changes in V˙O2 were significant until D50 and nonsignificant after that, the changes in ARC frequency and HR being significant at all stages studied. Thus, the developmental V˙O2 changes were contributed mainly by the slow morphogenetic processes during D19–D50, whereas changes in functional parameters began to play a role at later stages. The response to temperature fluctuations was mediated by a rapid change in functional parameters at all these stages.