Ecological specialization, rather than the island effect, explains morphological diversification in an ancient radiation of geckos

Island colonists are often assumed to experience higher levels of
phenotypic diversification than continental taxa. However, empirical
evidence has uncovered exceptions to this ‘island effect’. Here, we tested
this pattern using the geckos of the genus Pristurus from continental
Arabia and Africa and the Socotra Archipelago. Using a recently published
phylogeny and an extensive morphological dataset, we explore the
differences in phenotypic evolution between Socotran and continental taxa.
Moreover, we reconstructed ancestral habitat occupancy to examine if
ecological specialization is correlated with morphological change,
comparing phenotypic disparity and trait evolution between habitats. We
found a heterogeneous outcome of island colonization. Namely, only one of
the three colonization events resulted in a body size increase. However,
in general, Socotran species do not present higher levels or rates of
morphological diversification than continental groups. Instead, habitat
specialization explains better the body size and shape evolution in
Pristurus . Particularly, the colonization of ground habitats appears as
the main driver of morphological change, producing the highest disparity
and evolutionary rates. Additionally, arboreal species show very similar
body size and head proportions. These results reveal a determinant role of
ecological mechanisms in morphological evolution and corroborate the
complexity of ecomorphological dynamics in continent–island systems.