Physiological responses to acute changes in temperature and oxygenation in bird and reptile embryos

Environmental conditions considerably influence embryogenesis and subsequent postnatal development; however, the roles of individual embryonic physiological systems in these effects remain largely unclear. Data on the effects of some environmental factors (temperature variation and hypoxia) on the development of embryos and extra-embryonic organs in reptiles and birds are summarized, with special emphasis on acute changes in these factors. The involvement of several physiological characteristics related to the functions of the extra-embryonic membranes, cardiovascular system, and embryonic behavior (amnion rhythmic contractions, cardiac activity, and embryonic motility) in the integrated response to temperature fluctuations and acute hypoxia is considered. The changes in this response with embryonic age in reptiles and birds are analyzed. Particular attention is paid to the maturation of the regulatory mechanisms, interactions among the above parameters, and their possible contributions to the changes in oxygen consumption (or its stability) during short-term changes in temperature and oxygenation at different stages of embryonic development.