Chromosome variation, genomics, speciation and evolution in Sceloporus lizards

The clade of the North American lizard genus Sceloporus and its relatives comprising the subfamily Phrynosomatinae (Iguanidae) includes perhaps 150 evolutionary lineages. The work reviewed here begins with the discovery of the concentration of Robertsonian chromosomal variability in Sceloporus more than 40 years ago and cytogenetic and genomic evidence of remarkable chromosomal variation within the S. grammicus complex associated with narrow zones of hybridization between different chromosomal races. These discoveries led to hypotheses about hybrid zones involving negative heterosis, possible modes of chromosomal speciation, and the potential roles of such speciation in phylogenesis. The radiation of Sceloporus has now been studied by many different workers extending and mapping the geographic distribution of cytogenetic and genomic variation to understand the biology of the chromosomal variation and to establish the phyletic relationships of the various lineages. The result is a robust phylogeny and a large and still growing database of genic, cytogenetic and other biological parameters. These materials provide a rich series of natural experiments to support both synthetic-comparative and analytical studies of the roles of chromosomal variation, hybrid zones and modes of speciation in phylogenesis and evolutionary success.