Adaptive radiation is often a fundamental stepping-stone in the process of speciation. It occurs when a single ancestor diverges into several lineages with different ecological adaptations to exploit a variety of environments. This is assumed to have occurred during the terrestrial colonization of Jamaica by sesarmid crabs, giving rise to nine currently recognized species (genera Sesarma and Metopaulias). Today, these crabs can be found in a variety of different habitats throughout the island. While a recent study showed that all the endemic sesarmid species are monophyletic and gave an estimate for the time of colonization and divergence, it failed to resolve speciation events within the Jamaican monophylum. Therefore, at this point no conclusive information on the actual process of adaptive radiation can be gained out of this interesting evolutionary case. The current project will focus on the mechanisms of adaptive radiation by (i) using new molecular markers to better resolve the phylogenetic relationships among the Jamaican endemic crab species and by (ii) studying current processes leading to adaptive radiation, with the emphasis on ecological and genetic divergence at the population level. For comparison, the pseudothelphusid terrestrial crab fauna of the other Greater Antilles will be studied. This older lineage of land colonisers is ecologically and morphologically less diverged than the Jamaican Sesarmidae. Our study shall reveal whether an overall decreased intraspecific plasticity in the Pseudothelphusidae might be the cause for the lack of adaptive radiations in the past.
