Structural and physiological differences between montane and lowland avian eggs and embryos |
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Authors: | Cynthia Carey |
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Institution: | (1) Department of Environmental, Population and Organismic Biology, University of Colorado, 80309 Boulder, CO, USA |
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Abstract: | A few avian species breed at altitudes up to 6500 m. Embryos in eggs laid at high altitudes are confronted with the problem
that gases diffuse more rapidly at low barometric pressure than at sea level. Data on birds breeding up to 4500 m indicate
that modifications in eggshell structure and embryonic physiology foster successful development in these groups. At moderate
altitudes (up to 3600 m), shell conductance to gases (corrected to 760 torr) is decreased in approximate proportion to the
reduction in barometric pressure, thus offsetting the increased tendency of gases to diffuse. At altitudes above 4000 m, the
conductance is increased above levels at moderate altitudes, thus fostering improvement in oxygen availability, while increasing
rates of water and CO2 losses. Above 4000 m, embryonic physiological properties become increasingly important for coping with
hypoxic, hypocapnic, and dehydrated conditions inside the shell. Nothing is known about characteristics of eggshells and embryos
in eggs laid between 4500 and 6500 m. Despite years of artificial selection, domestic fowl do not breed successfully much
above 3000 m. Embryos of domestic fowl appear highly sensitive to the effects of hypoxia. |
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Keywords: | Hypoxia barometric pressure eggshell conductance hematocrit chorioallantoic membrane oxygen consumption blood gas tensions |
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