MUELLER, R.L.: Who needs a nucleus? Red blood cells in the genus Batrachoseps

Some species of lungless salamanders, family Plethodontidae, have blood containing enucleated red cells. Unlike nearly all mammals, which possess uniformly enucleated RBC’s, these salamanders have both enucleated and nucleated RBC’s present in their circulation at all times. In some cases, the percentage of enucleated red cells is as high as 99%. Despite its unique status among non-mammalian vertebrates, this blood condition has been relatively unstudied. Initial reports (Eisen, 1897) of the enucleated condition were from two species of Batrachoseps. In recent years, analysis of morphological and molecular data has shown Batrachoseps to be comprised of over twenty species, many as yet undescribed, with high levels of genetic divergence. Villolobos et al (1988) examined the blood of four species of Batrachoseps, two from each of the major clades (subgenera). Their results showed that species now assigned to the subgenus Batrachoseps have a high percentage of enucleated erythrocytes, while species of the subgenus Plethopsis have a low percentage of enucleated erythrocytes. A full understanding of the evolution of enucleated red cells must start with knowledge of the relative abundance of these cells in all extant members of the genus, coupled with a robust phylogenetic hypothesis. To this end, I examined the blood of ten individuals from each of twenty species. Results for the subgenus Plethopsis agree with previous reports; specimens have low numbers of enucleated cells. However, members of the subgenus Batrachoseps display substantial variation in numbers of enucleated cells. This variation exists both among different species and within a single species, and raises questions of ontogenetic and environmental effects on blood composition.