Rates of oxygen uptake increase independently of changes in heart rate in late stages of development and at hatching in the green iguana, Iguana iguana

Abstract

Oxygen consumption (VO₂), heart rate (f_H), heart mass (M_h) and body mass (M_b) were measured during embryonic incubation and in hatchlings of green iguana (Iguana iguana). Mean f_H and VO₂ were unvarying in early stage embryos. VO₂ increased exponentially during the later stages of embryonic development, doubling by the end of incubation, while f_H was constant, resulting in a 2.7-fold increase in oxygen pulse. Compared to late stage embryos, the mean inactive level of VO₂ in hatchlings was 1.7 fold higher, while f_H was reduced by half resulting in a further 3.6 fold increase in oxygen pulse. There was an overall negative correlation between mean f_H and VO₂ when data from hatchlings was included. Thus, predicting metabolic rate as VO₂ from measurements of f_H is not possible in embryonic reptiles. Convective transport of oxygen to supply metabolism during embryonic incubation was more reliably indicated as an index of cardiac output (CO_i) derived from the product of f_H and M_h. However, a thorough analysis of factors determining rates of oxygen supply during development and eclosion in reptiles will require cannulation of blood vessels that proved impossible in the present study, to determine oxygen carrying capacity by the blood and arteriovenous oxygen content difference (A-V diff), plus patterns of blood flow.

Keywords: Embryo; Growth; Heart rate; Iguana; Oxygen pulse; Oxygen uptake; Reptile.