Decoupling in Diversification and Body Size Rates During the Radiation of Phyllodactylus: Evidence Suggests Minor Role of Ecology in Shaping Phenotypes

Abstract

Empirical studies have shown that several taxa exhibit a decoupled relationship between lineage species diversification (the balance between speciation and extinction) and phenotypic diversification. This has been recognized by some authors as fundamental evidence for non-adaptive radiation. In the leaf-toed geckos Phyllodactylus of North America, there is a wide inter-specific overlap of phenotypic traits and high intra-specific morphological variation, despite predominantly allopatric distributions and the colonization of both insular and continental habitats. Here we demonstrate two outstanding aspects of the evolution of Phyllodactylus—first, that the radiation occurred with rate decoupling (body size and diversification), and second, that the contributions of island colonizations to the genus’ diversification (phenotypic and species) have been of the same magnitude as those of continental habitats. Phyllodactylus diversification has proceeded with minimal ecological influence, as suggested by the identification of limited phenotypic diversity, evidenced by the wide representation of one morphotype (shared in island and mainland environments) and limited disparity (body size and shape) for long periods of time. Conversely, some head traits like snout length have increased in disparity in recent times. Most likely, snout length is being shaped by selective pressures associated with the differential exploitation of insular and continental trophic niches. The decoupling of rates (diversification and body size evolution), long periods of morphological stasis (body size and shape), overlapping of traits in the morphological space, and minimal ecological influence on the evolution of body size suggest that Phyllodactylus has proliferated following the tempo and mode of a non-adaptive radiation.