An Aegean View on Non-Adaptive Radiations

The diversification of lineages sometimes exhibits patterns that are often described as ‘radiations’, which can be seen at various time scales, but researchers most often focus on a fast divergence of parental forms within short time spans. Adaptive radiations are widely discussed and have served as important showcases of Darwinian evolutionary processes. Other types of radiation have been identified, too, and several classifications have been suggested. Among these, ‘non-adaptive radiations’ remain controversial till today. Despite concerns on the conceptual basis of such a process, more and more cases of radiation that are described as ‘non-adaptive’ are published, and the continuously accumulating genetic/genomic data for more and more taxa seem to reveal extensive lineage diversification that is often not attributable to any apparent selective force. Given that allopatric divergence due to stochastic processes is presumably the cause of non-adaptive radiations, insular systems provide a rich pool of case studies. Using examples of lineage divergence from various taxa living on the Aegean islands, I discuss the processes leading to non-adaptive radiations in view of the alternative classifications of radiation by other authors, and show that such patterns may also result from a mixture of adaptive and non-adaptive processes.