Skull Characters and the Cladistic Relationships of the Hispaniolan Dwarf Twig Anolis

Abstract

Skull characters were examined and combined with postcranial osteological, external, allozyme, DNA sequence, and chromosome data from the literature to estimate the phylogenetic relationships of the Hispaniolan dwarf twig Anolis (A. sheplani, A. insolitus, and A. placidus). A survey of most species of Anolis species for which skeletons are available found two osteological character states unique to these species, a convex parietal roof and crenulated parietal edges, thus suggesting that the Hispaniolan twig dwarfs form a monophyletic group. To assess this hypothesis of monophyly and to estimate the phyletic placement of these species in the genus Anolis, parsimony analyses were undertaken including all proposed close relatives of the Hispaniolan twig dwarfs and a taxonomically and geographically diverse sample of congeners. Diagnostic synapomorphies found in this analysis were surveyed more widely in Anolis. Characterization difficulties of the skull data were addressed by using three coding methods to differentially code intraspecific and continuous variation. Confidence in the Hispaniolan twig dwarf relationships was assessed with the bootstrap, the test of Templeton, and the agreement between results from the three coding methods. The monophyly of the Hispaniolan twig dwarfs was strongly supported. The nearest relatives of the Hispaniolan twig dwarfs appear to be twig species from Hispaniola (A. darlingtoni), Puerto Rico (A. occultus), and South America (tigrinus group, i.e., A. solitarius), and Phenacosaurus. Wider taxonomic and character sampling is needed to assess the robustness of these clades, but present evidence suggests an invasion of Hispaniola or Puerto Rico from South America and, counter to the usual opinions of ecomorph occurrence by intra-island adaptive radiation, a clade of twig species on three different land masses.