Ontogenetic change in molecular and functional properties of blood of garter snakes, Thamnophis sirtalis

Abstract

At birth the blood of garter snakes (Thamnophis sirtalis) has high oxygen affinity (P50 at 25°C and pH 7.2 = 21 mm Hg), low hematocrit (14%), and a high proportion of inactive hemoglobin (44%). Growth of the snakes is accompanied by a steady decrease in oxygen affinity (P50 = 44 mm Hg in adults), increased hematocrit (to 44%), and decreased inactive hemoglobin (to 3%). These adult values are reached in the second or third year of a snake's life. There is a continuous change in the electrophoretically separable hemoglobin fractions during this period, but there is no ontogenetic change in the oxygen affinity of phosphate-stripped hemoglobin in solution. Organic triphosphates do not fully explain the ontogenetic change in blood oxygen affinity. Similar ontogenetic changes in blood oxygen affinity were found in two other species of snakes. The unusual morphology of snake lungs and consequent changes in pulmonary pO2 and pCO2 during ontogeny may be the basis for the unusual relationship between body size and blood oxygen affinity in snakes.