Evolution of Function and Form in Camelid Erythrocytes

The Camelidae, advanced artiodactyls of arid habitats, have unique erythrocytes among mammals. Mammals have advanced erythrocyte features surpassing those of other Vertebrata. Mammalia attained their biconcave disk form from ontogenetic phases recapitulating those in lower vertebrates, beginning with spheroid erythroblast precursors becoming ellipsoid, containing ellipsoid nuclei, mitochondria and other organelles. The mammals, however, continued development by regression of tubulin Marginal Bands, abortion of the nuclei, and DPG production within the erythrocytes instead of ATP produced from mitochondria or by anaerobic respiration. The camels evolved elliptical erythrocytes and kept them, by retaining the MBs. The abortion of the nucleus occurs and, nevertheless, the biconcave disk cannot form. The bilaminar, oval wafer is low in volume, about double in S/V , rich in Hb, and the many thin cells comprise a very low packed volume (and high plasma volume). The erythrocyte resists influx or outflow of water, as does the plasma, and helps the camelids during drastic dehydration. The blood flows normally even when the tissues are dehydrated. The bilaminar oval also helps in hypoxic montane habitats.