Search

Island colonists are often assumed to experience higher levels of phenotypic diversification than continental taxa. However, empirical evidence shows that exceptions to this “island effect” do exist. Here, we tested this pattern using a thoroughly sampled continent-island system, the genus Pristurus, a group of sphaerodactylid geckos distributed across continental Arabia and Africa and the Socotra Archipelago. We used a recently published phylogeny and an extensive morphological dataset to explore whether Socotran and continental taxa differ in their dynamics of phenotypic evolution. Moreover, we used habitat data to examine if ecological specialisation is correlated with morphological change, reconstructing ancestral habitat occupancy and comparing phenotypic disparity and trait evolution between habitats. We found heterogeneity in the outcome of the colonisation of the Socotra Archipelago. Namely, only one of the three events of colonisation has resulted in an increase in body size. However, in general, Socotran species do not present higher levels or rates of morphological diversification than continental groups. Instead, habitat specialisation provides a more nuanced insight into body size and shape evolution in Pristurus. In particular, the colonisation of ground habitats appears as the main driver of morphological change, producing the highest disparity and evolutionary rates. Additionally, arboreal species show very constrained body size and head proportions, suggesting ecologically driven morphological convergence. Our results reveal a determinant role of ecological mechanisms in morphological evolution and corroborate the complexity of ecomorphological dynamics in continental-island systems.