Respiratory and hematological physiology of day 15 chicken embryos (Gallus gallus domesticus) during water submergence and air recovery: Implications for bird embryos experiencing nest inundation

Bird nests of coastal or inland breeding birds can temporarily flood during high tides or storms. However, respiratory physiological disruption of such water submersion and implications for post-submergence survival are poorly understood. We hypothesized that respiratory physiological disturbances caused by submersion would be rapidly corrected following return to normal gas exchange across the eggshell, thus explaining survival of nest inundation in the field. We further hypothesized that the chicken embryo prior to hatching will develop the ability to recover from acid-base disturbance. We exposed day 15 embryonated chicken eggs (a well-studied point 3/4 through development) to half- or full submersion in water (producing moderate and severe hypoxia, respectively) or in mineral oil (anoxia) for periods of 2–24 h to create varying degrees of submersion-related respiratory and acid-base disturbances. Egg submergence was followed by up to six hours in air to determine the extent and rate of physiological recovery. Arterialized blood PO₂ and [lactate], acid-base and hematology were measured at frequent intervals (5 min to 2 h depending on tested variable) both during submersion and air recovery. Submersion in mineral oil – eliminating all gas exchange - proved lethal at two hours. Yet, calculated embryonic oxygen stores suggest submerged embryos should be able to maintain pre-submergence oxygen consumption for only ∼15 mins, suggesting a possibly adaptive immediate decline in metabolism upon submergence. Half- or full submergence in water created blood acid-base disturbances within as little as 5 min, with partial recovery towards the end of 24 h of submergence. Six hours of subsequent air recovery fully restored acid-base homeostasis. Hematological changes that appeared within 5 min of submersion - primarily red blood cell swelling - were eliminated within 1 h following return to air. Importantly, these data indicate a surprising resilience of the chicken embryo to temporary elimination of normal gas exchange which, if evident in other species, provides underlying mechanisms for surviving nest inundation.