The study of speciation has received renewed attention following the development of molecular markers to test evolutionary models in natural systems. Island lizards have proved particularly useful for the experimental investigation of differentiation at several taxonomic levels. This thesis examines the patterns and processes of divergence within and among species, using a range of genetic techniques, in two Lesser Antillean lizards, Anolis and Sphaerodactylus.
An assessment of the AFLP technique was initially undertaken to establish its utility in differentiating between groups of lizards at various taxonomic levels in Anolis. The results demonstrated that AFLPs are highly effective for species discrimination, but at finer taxonomic levels, within group variability can inhibit between-group differentiation. A modification to standard multivariate analysis is described that enables a clearer population signal to be extracted from AFLP data.
To allow an investigation of intraspecific divergence within Anolis roquet, eight
microsatellite loci were developed and employed together with morphological
analysis along six experimental transects on Martinique. Reduced gene flow was
demonstrated in several regions using pairwise F_ST estimates. In the north of the
island adaptive divergence for habitat type, not phylogenetic lineage, was identified as the factor influencing the current morphological and genetic population structure. In the south of the island however, it was not possible to isolate a single cause for the observed distribution of A. roquet.
An examination of the Sphaerodactylus radiation throughout the Lesser Antilles
using phylogenetic reconstruction of mitochondrial cytochrome b sequences
revealed high levels of inter-island divergence within nominal species, suggesting that several taxa warrant reclassification. Phylogeographic evidence indicated that a single rapid colonisation event was probably responsible for the spread of Sphaerodactylus down the archipelago.
The implications of this work are discussed in relation to the application of
molecular markers in evolutionary research and current views on the mechanisms of speciation.