Erythropoiesis in the Diploid and Tetraploid Odontophrynus americanus: An Evolutionary Approach in These Cryptic Species (Amphibia, Anura, Leptodactylidae)

Abstract

Polyploidy is one of Nature’s strategies to create diversity among fauna and flora, resulting in new species. We have used light, scanning and transmission electron microscopy to perform morphometric analyses in maturing erythroid cells of the cryptic species diploid and tetraploid Odontophrynus americanus frogs. Normal blood of both specimens contained 97%–99% erythrocytes and 1%–3% reticulocytes, besides thrombocytes and leucocytes. Mature erythrocytes were flattened, ellipsoidal, nucleated, with cytoplasm rich in haemoglobin. Five days after being made anaemic, 15% and 33% of diploid and tetraploid red blood cells respectively, were in an immature stage, basically proerythroblasts. These cells were also seen at the 10th day, in addition to basophilic and polychromatophilic erythroblasts. By day 15 a higher number, 75% and 89% of reticulocytes in earlier maturation stage was found, respectively. At day 20 of recovery from anaemia, there were 63% and 85% of reticulocytes, respectively, most in an advanced stage of maturation. The number of immature cells then gradually decreased at days 30 and 50. Cytoplasmic inclusions similar to Heinz bodies were found in these cells associated with RNA or RNP. Morphometric analysis showed that the tetraploid erythroid cells synthesise 30% more ribosomes than the diploid erythroid cells. The density of ribosomes/μm2 allowed these cells to be classified into seven classes: proerythroblasts, basophilic erythroblasts I and II, polychromatophilic erythroblasts I and II, reticulocytes and erythrocytes. Such morphometric strategy suggested that gene activity was more intense in the tetraploid maturing erythroid cells, despite the marked tendency of these tetraploid cells towards diploidisation of the genome expression.