J.W.Sites, J.W.Archie, C.J.Cole, O.F. Villela
Species of Sceloporus have figured prominently in studies of population, community, and physiological ecology, social behavior, disease transmission, and biogeography, probably in large part because of the broad distribution of the genus in a variety of habitats, its species diversity, and the diurnal and conspicuous habits of most species, which are often locally abundant. Despite these advantages and the prevalence of Sceloporus in many research programs in organismal biology, many outstanding systematic and evolutionary problems remain, and the Sceloporus radiation has not been rigorously studied from a contemporary phylogenetic perspective. We have undertaken this review with two major objectives: (1) to summarize all information relevant to existing phylogenetic hypotheses for the genus, and make it available in a single document
and (2) to point out some of the ecological and evolutionary questions for which Sceloporus is superbly suited for detailed study, within the context of well-corroborated phylogenetic frameworks. With respect to the first objective, we have summarized the major phylogenetic conclusions of Smith, Larsen and Tanner, Cole, and those based on the largely unpublished cytogenetic data sets of W. P. Hall and C. J. Cole. Alternative hypotheses are compared and summarized with regard to major points of congruence and conflict, and we argue that thorough contemporary systematic studies are urgently needed for the entire Sceloporus radiation. With respect to the second objective, the Sceloporus radiation unequivocally shows three or more independent origins of viviparity, possibly five independently derived heteromorphic sex-chromosome systems, and perhaps six examples of independent secondary loss of sexual dimorphism in color pattern, regardless of which of the existing phylogenetic hypotheses most closely reflects the real evolutionary history. Different radiations within the genus also continue to offer challenging problems in historical biogeography, speciation, macroevolution, hybrid zone dynamics, taxonomy at the species level, population biology, physiological ecology, and comparative ethology. The genus also offers additional potential in relatively unexplored areas such as mate choice/sexual selection, the roles of regional gene duplication in genome evolution and co-speciation/co-adaptation of host-parasite systems. This potential, particularly great because of the species diversity of the genus, is discussed within the context of comparative biology and phylogenetic inference.