The Relationship between Body Size and Blood Oxygen Affinity in Snakes

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Abstract
Blood oxygen affinity of 15 species of colubrine snakes is related to body size by the equation . Blood oxygen affinity of snakes in six other families did not differ from values predicted for colubrines of the same body size. An ontogenetic decrease in blood oxygen affinity was found in three of four species for which adequate samples were available. This ontogenetic change was seen only in whole blood; there was no ontogenetic change in oxygen affinity of hemoglobin in solution. The decrease in blood oxygen affinity with increasing body size (ontogenetic growth or adult body size) in snakes contrasts with the increase in oxygen affinity with increasing body size in mammals, birds, and lizards. The difference in blood oxygen affinity probably reflects the differences in pulmonary gas concentrations produced by specialized lung morphology and breathing movements of snakes.