Ontogenetic modification of the hypercapnic ventilatory response in the zebra finch.

We investigated the effect of exposure to CO2 during development on the adult ventilatory response to CO2 of zebra finches. Developing zebra finches were exposed to chronic hypercapnic respiratory environments as embryos, as nestlings or during both developmental periods. Their responsiveness to CO2 was then measured following a 125-135 day post-fledging deacclimation period. At a FICO2 of 0.06, mean ventilation of adult finches in the three groups was 74.8, 61.3 and 65.8%, respectively, of that of finches reared under normocapnic conditions. These data indicate that adult acute ventilatory responsiveness to CO2 in birds may be in part determined by CO2 exposure during early development and may help explain the observation that fossorial and semifossorial species of birds and mammals, that naturally encounter high CO2 conditions in their burrows, have a blunted hypercapnic ventilatory response.