Evolution of lizards on islands

Dr. Richard Brown, Reader in Animal Evolution, analyses evolution processes on islands, building on existing studies in the Caribbean, Hawaiian, and Canary Islands.

Islands have long been the source of fascination for scientists, most notably Darwin who formulated the Origin of the Species after studying organisms on several islands during his journey around the world on the HMS Beagle. They have consequently provided important testing grounds for evolutionary theories.

One aspect of his research investigates differences in genetic structure between lizards of the genus Gallotia and Chalcides within the Canary Islands. This aims to discover what has caused lizards on the same island to evolve differently.

For example, an analysis of G. galloti on Tenerife investigates the possibility that catastrophic landslides, such as the one that occurred 800,000 years ago in the Güimar valley on Tenerife, can mould natural phylogeographical breaks (‘phylogeography’ is the study of the geographical distributions of evolutionary lineages). Although landslides are common events during the formation of oceanic islands around the world, the phenomenon have received relatively little attention from biologists up until now.

Tomato-baited traps were used by Dr. Brown’s research team to capture lizards from 18 sites along a 60-km transect across the Guimar valley. Mitochondrial DNA and morphology (the shape, colour, structure, and pattern of a species) were then studied in the captured specimens (which were all released). Three main genetic lineages were detected, which meet across the Guimar valley. The valley also coincides with a change in the scalation of female lizards, but not males. These findings provide support for the theory that the debris avalanche has had a significant impact on the phylogeography of Gallotia galloti and may even have been a primary cause of the within-island evolutionary splits, by causing population fragmentation and isolation.

At a more general level, the team concluded that, “The frequent occurrence of similar landslide events in volcanic islands, together with the fact that within-island variation appears widespread in small oceanic islands, suggests that such events may play a significant role in shaping within-island diversity.”

The paper “Geological history and within-island diversity: a debris avalanche and the Tenerife lizard Gallotia galloti” was published in the journal Molecular Ecology in 2006.
A list of Dr. Brown’s research papers can be viewed here.

Page last modified 18 January 2008.

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