Evolution of isozyme characters in the tuatara,Sphenodon punctatus

Abstract

Abstract Isozyme characters of the tuatara, Sphenodon punctatus, were examined by starch gel electrophoresis. The characters investigated included: (1) the number of presumptive structural gene loci encoding for each of 30 enzyme systems; (2) the formation of interlocus heteropolymers in polymeric, multilocus enzyme systems; and (3) the tissue-specific distribution of 51 presumptive structural gene loci among 15 tissues. The number of loci controlling the various enzyme systems in the tuatara was similar to that reported in other vertebrates. No unexpected duplicated loci were observed although some silencing may have occurred. All anticipated interlocus heteropolymers were observed, except for dihydrolipoamide dehydrogenase; most loci were widely distributed among the tissues examined. With respect to the first two characters, Sphenodon appears to exhibit the primitive condition. However, analysis of the tissue-specific distribution of loci suggests that, when compared to other members of the class Reptilia, the tuatara is not necessarily the most primitive taxon. For this character, the tuatara appeared more primitive than the prairie rattlesnake yet more derived than the American alligator. The results suggest that isozyme characters may be of value in examining both the intra- and interpopulation genic variability of the tuatara as well as the phylogenetic relationships of Sphenodon and other reptilian taxa.