Gas diffusive conductance of sea-level hen eggs incubated at 2900 m altitude

Abstract

Sea level hen eggs, selected for their shell conductance (water vapor conductance, H H 2O ), were incubated at a simulated high altitude, P b = 529 Torr , ca. 2900 m, at 72% relative humdity (rh) to prevent excessive water loss due to hypobaric condition; they were transferred to 150 m 18–24 h before measurements. Control eggs were incubated at 150 m, P b = 750 Torr, rh = 60% . In 8- to 18-day embryos, total CO diffusive conductance, G CO; embyronid body mass, BM; oxygen consumption, Ṁ O 2 ; blood hematocrit, Hct; hemoglobin concentration, [Hb]; and heart mass, HM, were measured. Total water loss was the same in both groups, 12% initial egg mass. However, the severe effects of high altitude: 72% mortality and 9% malformation, and reduced increases of BM and Ṁ O 2 , can be related partially to the strong hypocapnia, which resulted from the high shell conductance (G H 2O = 18.1 mg·(d·Torr) −1, and was superimposed on the hypoxia. G CO was reduced, while Hct, [Hb] and HM were not significantly affected. When measurements. were normalized to BM, Ṁ O 2 and G CO were identical in the two groups, whereas [Hb] and HM were higher at 2900 m (differential growth). Thus, during incubation, gas diffusive conductance appeared to depend on embryo development and did not adapt to altitude hypoxia. Compared with controls, G CO in high-altitude eggs actually decreased in proportion to BM growth.