Quantitative Variations in the Nuclear DNA and Phylogenesis of the Amphibia

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Abstract
Using blood smears, stained with Feulgen's reaction, a study has been made of the nuclear DNA content of an Apode, thirteen species of Urodela and twenty-three species of Anura, certain of which belong to old and important families on account of the complex phylogeny of these Amphibia. The results of this study emphasize the existence of extensive interspecific variations in the amounts of DNA in the Amphibia, as well as certain facts of possible systematic interest: the Urodela possess greater amounts of nuclear DNA than most of the Apoda and the Anura; however, some of the more primitive species existing today (genus Hynobius) have DNA amounts that are relatively low in the order; in the Amphibia, the variations in the DNA amounts do not seem to be correlated with the behaviour of the phylogeny but seem rather to reflect phenomena of redundancy. The theories that have been put forward so far on the significance of the quantitative variations in the DNA of the Amphibia seem to be at least partly conflicting: in fact, certain authors maintain that similar variations represent an important mechanism in the evolution of the Vertebrates, whereas others consider that they should rather be related to adaptive phenomena. The problem of the significance of these variations is discussed, account being taken of the latest discoveries on the presence and characteristics of the repetitive DNA fractions in the eukaryotes in general, and in the Amphibia in particular, as well as of the possible prospects offered by these researches for a study of this problem.