No abstract

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.

The shape of the tree of life is the result of shifting diversification rates, and identifying the factors driving these shifts is one of the main aims in evolutionary biology. Various biotic and abiotic factors have been proposed to have an impact on mammal diversification, such as climatic and tectonic changes, the acquisition of new traits, and expansion into new ecosystems or landmasses. We used phylogenetic comparative methods to quantify the influence of potential drivers on diversification patterns in extant squirrels (Sciuridae, Rodentia). We conducted a multilayer approach, comparing diversification rates among squirrel lineages depending on their degree of biome specialisation, biogeographic realm occupancy, locomotion adaptations, and presence in mountainous regions. We generated the most complete phylogeny of squirrels to date, encompassing almost 80% of the extant species, and applied multiple and binary state‐dependent diversification models. All the traits examined showed an influence on diversification rates. The biome specialist lineages showed the highest speciation rates, suggesting a major role of bioclimatic specialisation on macroevolutionary patterns. A single major event, the Miocene–Pleistocene radiation of terrestrial‐adapted lineages in North America, left a signal that was recovered in two of our analyses. Both the Nearctic lineages and the terrestrial‐adapted lineages showed high speciation rates, highlighting the fact that that major evolutionary episodes may produce confounding effects in state‐dependent diversification models. Ancestral reconstructions showed that cold and warm intervals in Earth’s history had different effects on squirrels’ diversification, depending on their climatic affinities. Tropical and arboreal squirrels evolved predominantly in the warm intervals, while terrestrial and cold‐adapted squirrels radiated in the cold intervals. Our findings suggest that, while global climatic shifts are key for the speciation processes in mammalian lineages, lineage‐specific ecological adaptations are critical modulators of the responses of lineages to such environmental shifts, in an interplay that ultimately affects their diversification patterns.