PARALLEL WITHIN-ISLAND MICROEVOLUTION OF LIZARDS ON NEIGHBORING ISLANDS

THE correlation of changes in morphological traits with environmental gradients is often taken as evidence for natural selection 1. But in many cases, the possibility that this correlation is coincidental cannot be ruled out 2. Stronger evidence for natural selection is provided when closely related allopatric species show parallel patterns of geographic variation along similar environmental gradients. Vertebrate geographic variation within small islands provides a valuable opportunity to detect mechanisms of natural selection 3-5. We have now studied microgeographic variation in the colour patterns of two skinks (Lacertilia: Scincidae) from neighbouring heterogeneous islands. Parallel north-south variation occurs in the colour patterns of both species. Populations from the south of both islands possess conspicuous dorsal-tail coloration. Morphological distance matrices for both species are compared with similar aspects of environmental variation using simultaneous Mantel tests. This indicates that differential selection between lush and arid habitats is the primary cause of the variation in colour pattern.