Island lizards offer new twist on theories of evolution

In the footsteps of Darwin, scientists have been studying the evolution of separate groups of the same species on island habitats. And they have discovered evidence of a new twist to the Father of Evolution’s narrative on which species change and why.

For, whereas the Victorian pioneer noted differences in Galapagos tortoises of the same species living isolated from each other on different islands, these fresh observations recount a similar change in lizards living on the same island and regularly exchanging genes.

“For many years it was believed that divergence of animal populations was unlikely if the animals were exchanging genes and that this counteracted the selection pressures of different environments. That seems not to be the case,” explained Richard Brown, Professor of Animal Evolution at Liverpool John Moores University and lead author of the study published today (February 3, 2023) in Communications Biology.

Professor Brown and his team identified a species of lizard that lives on grey shingle beaches on the island of Madeira but is also abundant in all other habitats on the island. His colleague, Dr Carlo Meloro found that the lizards on different beaches were distinct. For example they had darker bodies and broader snouts relative to inland populations that were less than 1km away.

They applied gene flow modelling to their genomic data and showed that pairs of neighbouring inland and beach populations were indeed exchanging genes. These patterns were repeated across all four studied beaches in different parts of Madeira, confirming similar gene flow among populations.

The study suggests that strong differences in natural selection are able to overcome the diluting effects of gene flow, leading to divergence.

Professor Brown says the work adds to other recent findings on some invertebrates which are adding weight to this shift in evolutionary biology thinking - in terms of our understanding of how populations (of the same species) diverge. While it now appears that divergence can occur in the face of gene flow, what remains to be seen is how important this has been in terms of the formation of new species.