The evolution of erythrocytes and oxygen delivery in vertebrate animals: Introduction

This manuscript provides a brief introduction and overview of four companion papers that focus on the evolution of oxygen uptake and delivery to tissues. Although major emphasis is placed on the characteristics of erythrocytes and the hemoglobin they contain and how these characteristics vary by taxa in response to environmental influences and metabolic requirements, the accompanying evolution of the cardiovascular and respiratory systems and their interactions with erythrocytes are also discussed. In addition, the similarities and differences in erythropoiesis and the presence of immature erythrocytes in blood across taxa are presented.