Evolutionary history of Lost World frogs

The flattop mountains (tepuis) of South America are ancient remnants of the Precambrian Guiana Shield plateau. The tepui summits, isolated by their surrounding cliffs that can be up to 1000m tall, are thought of as 'islands in the sky,' harboring relict flora and fauna that underwent vicariant speciation due to plateau fragmentation. High endemicity atop tepui summits supports the idea of an ancient 'Lost World' biota. However, recent work suggests that dispersal between lowlands and summits has occurred long after tepui formation indicating that tepui summits may not be as isolated from the lowlands as researchers have long suggested. Neither view of the origin of the tepui biota (i.e., ancient vicariance vs. recent dispersal) has strong empirical support owing to a lack of studies. We test diversification hypotheses of the Guiana Shield highlands by estimating divergence times of an endemic group of treefrogs, Tepuihyla. We find that diversification of this group does not support an ancient origin for this taxon; instead, divergence times among the highland species are 2–5 Ma. Our data indicate that most highland speciation occurred during the Pliocene. Thus, this unparalleled landscape known as “The Lost World” is inhabited, in part, not by Early Tertiary relicts but neoendemics. 1 Salerno PE, Ron SR, Señaris JC, Rojas-Runjaic F, Noonan BP and Cannatella DC. 2012. Ancient tepui summits harbor young rather than old lineages of endemic frogs. Evolution 66(10): 3000–3013 – PES obtained samples and collected, performed analyses, and did most of the writing; SRR, JCS, FRR, and BPN contributed with samples, data collection, and writing; DCC contributed with analyses and writing. 2 INTRODUCTION The tepuis (flattop mountains) of northern South America are arguably the most dramatic example of sky islands on Earth. With relatively flat summit plateaus sitting atop sheer cliffs of up to 1000m, these tabletop mountains form a discontinuous ecosystem called Pantepui (Huber, 1988) and harbor numerous endemic lineages. For example, within the Pantepui, 60% of the vascular plant species and 87% of the frog species are endemics, often to a single tepui summit (Berry and Riina, 2005; Duellman, 1999; McDiarmid and Donnelly, 2005). The tepuis are part of the Guiana Shield, which is situated between the Orinoco and Amazon Basins, accounts for 9% of the land area of South America, and shows biogeographic affinities with the Amazon and Andes. Early reports of the unique topography and biodiversity of the Pantepui inspired Sir Arthur Conan Doyle to write of long-isolated dinosaur populations surviving to the present day in his novel "The Lost World," which inspired the namesake Lost World Hypothesis (Rull, 2004a; or Plateau Hypothesis, Chapman, 1931), which is the main biogeographic hypothesis put forward to explain the highly endemic fauna and flora of this region (Chapman, 1931; Maguire, 1970; Hoogmoed, 1979; McDiarmid and Donnelly, 2005; Heinecke et al., 2009). This hypothesis predicts that highland species, which are often endemic to a single tepui, are relicts of formerly widespread plateau taxa and arose through vicariance following ancient fragmentation of the plateau. Thus, summit taxa are hypothesized to have been isolated for millions of years. In examining the especially high endemism levels of Pantepui frog genera, most researchers support the idea that diversification must be explained, at least partially, by long-term isolation of Plateau