Meeting Abstract

P3.43  Jan. 6  Allometry of Hematological Parameters in Birds: A Phylogenetic Approach WAGNER, E.C.*; WILLIAMS, T.D.; Simon Fraser University ewagner@sfu.ca

The allometric scaling of metabolic rate across animal species has long been a subject of interest in comparative biology. Our objective here is to provide a functional explanation for this general pattern in birds by characterizing hematological parameters (i.e. hematocrit, erythrocyte size and number) which essentially represent oxygen carrying capacity and are consequently reflected in measures of overall metabolic activity. On a mechanistic level, small erythrocytes have a greater surface area to volume ratio and a shorter diffusion pathway, facilitating transfer of oxygen and carbon dioxide between blood cells and target tissues. A higher number and relative proportion of red blood cells (hematocrit) in the blood also increases viscosity and reduces flow rate, thereby reducing heat loss, a critical determinant of metabolic activity in endotherms. It follows that a strong selective pressure should exist among small organisms with higher mass-specific metabolic rates for a greater number of smaller, more efficient red blood cells to meet enhanced oxygen demands. We confirmed these hypotheses with traditional comparative analyses, and then re-examined the allometric relationship using the independent contrasts approach to control for phylogenetic effects. Independent of body mass effects, differences in blood parameters across taxa would be expected due to adaptation to varying oxygen demands of divergent life history patterns, habitats, and ecological niches. We found that controlling for phylogeny resulted in a less significant relationship between hematological parameters and body size, indicating that the while the allometric relationship between these variables is robust, it is also strongly influenced by shared characteristics among closely related species.