MITOCHONDRIAL-DNA SEQUENCE-BASED PHYLOGENY AND THE EVOLUTION OF VIVIPARITY IN THE SCELOPORUS-SCALARIS GROUP (REPTILIA, SQUAMATA)

The lizard genus Sceloporus contains both oviparous and viviparous spe cies. The scalaris complex is the only monophyletic group within the g enus that Includes both reproductive modes, thus it is particularly we ll suited for studies of the evolution of viviparity. Approximately 87 4 nucleotides of mtDNA sequence data, collected from 38 specimens, com prising 25 populations of all five recognized species within the group , were used in a phylogenetic analysis of the origin of viviparity. Vi viparity appears to have evolved twice in this group: once in S. goldm ani, included in a clade formed by a northern group consisting of S. s calaris, S. chaneyi, and S, goldmani, and one more time in S. bicantha lis, included in the southern group formed by S. bicanthalis and S. ae neus. An oviparous population of S. bicanthalis nested within that viv iparous clade, indicates that reversal from viviparity to oviparity ma y be possible. Degree of sequence divergence among several S. bicantha lis individuals pertaining to a population in which both parity modes occur, was no larger between oviparous and viviparous Lizards than amo ng viviparous lizards. This suggests that this population is a single species, and it may represent a transition from oviparity to viviparit y or vice-versa.