Molecular and morphological evolution within small islands

Although explicit rules can be used to hypothesise an inter-island colonization sequence from a molecular phylogeny, and statistical methods can be used to assist in partitioning historical factors from current selective factors, this latter process has limited efficacy where there are a limited number of islands. Studying numerous populations within small, but heterogenous, islands allows a better understanding of the factors causing geographic variation. Three main approaches have been used to study within-island geographic variation using lizards on Canarian and Lesser Antillean archipelagos: (i) matrix correspondence tests and their partial regression/correlation extensions on morphological and molecular data; (ii) identification of within island patterns of morphological geographic variation paralleled on independent islands; and (iii) large scale field experiments on selection. These studies reveal that, even on small islands, ‘island populations’ may not be homogeneous in morphology, or molecular phylogeny, and that natural selection for current ecological conditions appears to be a primary force influencing morphological population differentiation, irrespective of phylogenetic history.