Allometric and Phylogenic Comparisons of Circulating Leukocyte Concentrations between and within Birds and Mammals

The blood concentrations of leukocytes and the major classes of leukocytes were compared across over 200 species of birds and over 300 species of mammals based on phylogenic relations, body weight and diet. The concentration of leukocytes was markedly higher in birds than mammals reflecting elevated concentrations of all major classes but particularly those of lymphocytes, monocytes, eosinophils and basophils. Overall, there were no differences between blood leukocyte concentrations in placental and marsupial mammals. There were differences between leukocytes concentrations within the placental mammals, for instance being lower in mammalian species within the taxa Glires than in Laurasiatheria and Primatomorpha which in turn are lower than in Afrotheria and Xenarthra. There were also differences in leukocyte concentrations in birds being higher in species with the taxa Afroaves than in Australaves. There were phylogenic differences in the percentages of the leukocyte classes. For instance, in placental compared marsupial mammals, the percentage neutrophils is elevated, the percentage lymphocytes is depressed and neutrophil to lymphocyte (N:L) ratio was much higher. Moreover, the percentage heterophils is high, the percentage lymphocytes is low and heterophil to lymphocyte (H:L) ratio is greater in birds from the taxa Paleognathae than the Neognathae. There was a positive relationship between concentrations of leukocytes or neutrophils and log body weight.