More than just the numbers—contrasting response of snake erythrocytes to thermal acclimation
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Acclimation to lower temperatures decreases energy expenditure in ectotherms but increases oxygen consumption in most endotherms, when dropped below thermoneutrality. Such differences should be met by adjustments in oxygen transport through blood. Changes in hematological variables in correspondence to that in metabolic rates are, however, not fully understood, particularly in non-avian reptiles. We investigated the effect of thermal acclimation on a snake model, the grass snakes (Natrix natrix). After 6 months of acclimation to either 18 °C or 32 °C hematocrit, hemoglobin concentration, erythrocyte number, and size were assessed. All variables revealed significantly lower values under warm compared to cold ambient temperature. Our data suggest that non-avian reptiles, similarly as birds, reduce erythrocyte fraction under energy-demanding temperatures. Due to low deformability of nucleated erythrocytes in sauropsids, such reduced fraction may be important in decreasing blood viscosity to optimize blood flow. Novel findings on flexible erythrocyte size provide an important contribution to this optimization process.
KeywordsTemperature acclimation Reptile Ectotherm Cell size Nucleated erythrocytes
We thank four anonymous reviewers for their valuable comments on the manuscript.
This study was supported by grants from the National Science Centre, Poland, to SB (grant no. UMO-2016/21/N/NZ8/00959), UB (grant no. UMO-2013/11/B/N28/00907), and DS of Jagiellonian University (DS/WIBNOZ/INOS/757).
Compliance with ethical standards
Snake collection and experimental procedures were performed according to the permits from II Local Ethical Committee (permit no. 132/2016 from 26.05.2015) and Regional Directory of Nature Conservation (permit no. OP-I.6401.21.2015.PKw from 2.07.2015) in Cracow.
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