THE PHYLOGENETIC ODYSSEY OF THE ERYTHROCYTE .4. THE AMPHIBIANS

Amphibians manifest permanently nucleated, oval, flattened, biconvex e rythrocytes. These cells demonstrate a cytoskeleton which is responsib le for their morphogenetic conversion from a sphere to an ellipse and imparts to their cellular mass reversibility of traumatic deformation. The class Amphibia has the largest of all erythrocytes attaining volu mes greater than 10,000 femtoliters in the Amphiuma. The large dimensi ons reflect evolutionary processes, genomic size, ploidy and the relat ive size of other somatic cells. Conversely, the erythrocyte count and hemoglobin concentration of these species are low. Occasional denucle ated red cells can be seen in the peripheral blood but may attain leve ls of 90-95% of the total circulating population in certain members of the tribe Bolitoglossini (e.g. Batrachoseps attenuatus). These erythr oplastids retain the marginal band thus remaining different from mamma lian erythrocytes. Embryologically, erythropoiesis initiates in the yo lk sac and then progresses to the kidney, liver, and possibly spleen. The yolk sac cohort is transitory and is successively replaced by the larval and definitive populations of erythrocytes. Red cell production (along with thrombocytopoiesis) in adult urodeles is conducted intrav ascularly in the spleen. In anurans this organ is usually the major si te although the liver also serves as a secondary locus for this activi ty. Medullary (bone marrow) erythropoiesis makes its phylogenetic debu t in anurans and typically occurs during heightened hemopoiesis follow ing metamorphosis or hibernation. Maturation of the erythrocyte in the circulation is commonplace (especially in urodeles) while proliferati on at this site is inducible by splenectomy and/or hemolysins. Erythro cyte-related values demonstrate variable differences associated with a ge, weight, season, gender, and environment.