Chromosomal Evolution in the Diplodactylinae (Gekkonidae, Reptilia) .1. Evolutionary Relationships and Patterns of Change

A chromosomal analysis of 47 species of diplodactyline gekkos indicates that these are a monophyletic assemblage derived from a 2n = 38 acrocentric ancestral karyotype. Four major clades are present, the first possessing the ancestral karyotype. The remainder are defined by the possession of a series of shared derived chromosomal rearrangements, or by the type of chromosome change. The first of these derived clades includes the subgenus Strophurus, which has five fixed, presumed pericentric inversion differences. The second includes members of the D. vittatus species group. Here, a number of chromosome fusions have been established which appear to have been associated with speciation. The third derived clade is distinguished by 19 fixed, presumed pericentric inversions, and includes the genera, Oedura, Rhacodactylus, Bavayia, Pseudothecadactylus, Carphodactylus and Hoplodactylus. It is argued that the 2n=38 acrocentric karyotype common to many of the species is the ancestral karyomorph, and the modifications of this format have been achieved by both chromosome fusion and pericentric inversion. The decision that this is the ancestral karyomorph was based on its dominance in extant species; the fact that similar karyotypes are present in other gekkonid subfamilies (effective out-groups), that 2n =38 all acrocentric ancestral karyotypes are also found in some other lizard families, and that such a diversity of rearrangements was established, provide arguments against any other viable ancestral format. Two discrete modes of chromosomal repatterning are found in the Diplodactylinae: the fixation of presumptive multiple pericentric inversions, producing a karyomorph which characterises large groups of species; and the fixation of fusion or presumptive inversion differences which distinguish individual species or chromosome races. The latter appear to have been associated with speciation. It is clear that in certain groups, such as the Strophurus species group (the members of which all share a derived karyomorph defined by the presence of five inverted chromosomes), speciation has proceeded without gross chromosomal rearrangements.