Figure 1 The tepui ecosystems. Show full caption (A) Mount Roraima, an emblematic tepui. (B) Map showing part of the Eastern Pantepui region, highlighting the highest and most isolated tepuis sampled in this study (numbered from 1 to 11), and table indicating estimates of divergence time among these tepuis, or between these tepuis and the surrounding uplands, based on genetic divergences in ND1 (see Supplemental information for details).

We used a comprehensive sampling of five Pantepui amphibian genera (Anomaloglossus, Oreophrynella, Pristimantis, Stefania and Tepuihyla) and one reptile family (Gymnophthalmidae) — the most conspicuous vertebrates on tepui summits — from 17 tepuis in the Eastern Pantepui region and surrounding uplands. If individual tepui summits were indeed reservoirs of ancient endemism, phylogenetic analyses of these taxa would identify genetically distinct populations on each tepui without close relatives elsewhere. Instead, analyses of two mitochondrial gene fragments evolving at different rates (16S rDNA and ND1 mtDNA; see Supplemental information ) indicate that populations of a given species on individual summits are often closely related to those on other summits (e.g., Oreophrynella), or to those from the surrounding uplands (e.g., Tepuihyla). Uncorrected pairwise distances in both genes indicate unexpectedly low genetic divergence — as low as zero — among multiple tepui summit species or populations in five of the six groups (Stefania being the only exception), as well as among some summit species or populations and uplands populations described as distinct species ( Figure 1 B; Supplemental information ). Some of the lowest genetic distances are observed for populations that are currently recognized as distinct species and show striking phenotypic differences. For instance, the inconspicuously black ventral coloration in the toad Oreophrynella nigra (Yuruani-tepui and Kukenan-tepui) differs markedly from the potentially aposematic yellow–orange–black color contrasts in O. quelchii (Mt. Roraima and Wei Assipu-tepui), despite pairwise distances of 0.63–0.95% in ND1 and zero in 16S between both taxa. The absence of genetic uniqueness suggests that the majority of these summit populations were only recently isolated. To provide an approximate estimate of the timing of their isolation, we used a nonlinear regression analysis that corrects for substitutional saturation and the systematic underestimation of evolutionary rates in recent divergences ( Supplemental information ). Our analyses suggest that 10 of the 11 most inaccessible tepuis studied show evidence for one or multiple instances of gene flow with other summits or with surrounding areas as recent as the late Pleistocene-Holocene (<1.8 mya; Figure 1 B).