The tepuis of South America are unique flat-topped mountains rising 3000m above the Guiana Shield. Many researchers believe the enormous species endemism found in tepuis is a result of millions of years of isolation atop summits. However, it is likely that the story is much more complex, involving recent dispersals and responses to climatic shifts. This project will investigate the role of isolated tepuis on diversification using two main approaches: (A) estimations of when species within a highland-restricted frog group diverged, to determine if they have been isolated atop summits since tepui formation (about 70 mya) or dispersed more recently; (B) estimation of population connectivity among three tepui summits, to determine the effect of tepui landscape on genetic parameters of two summit endemic species.
Because tepuis are some of the most drastic landscape features on earth, this study is a significant contribution to understanding the effects that drastic landscapes such as sky islands have on population connectivity, and thus on impacting levels of biodiversity. Additionally, this research will build partnerships with international scientists and train students in phylogenetics, population genetics, and biodiversity research.
The Lost World of South America is a system of more than 100 flattop mountains, a fascinating ecosystem that once inspired Sir Arthur Conan Doyle to write a novel of the same name as well as more recently Disney's Movie UP. However, due to its high inaccesibility, little research has been done for us to begin to understand the evolutionary origins of this Lost World. In this project, we collected samples of several summit endemic (unique) frogs, and challenged the long-standing hypothesis that endemics had been isolated for millions of years atop these mountains. Are these summit endemics recent immigrants to the Lost World? We also aimed to understand and measure the effect of these extreme landscapes on population's movements across summits. How easy are 2000 foot vertical walls to cross? 1. Are Lost World frogs really lost? The tepuis (flattop mountains of the Lost World of S. A.) were formed after millions of years of erosion of a high-altitude plateau. The mountains are the remnants of this plateau, and were formed approximately 90 mya. Given their geologic history, people traditionally thought that endemic summit species must have been isolated since tepuis were formed. However, in our study we found that highland endemic frogs had in fact arrived to the summits millions of years after these mountains were formed (only within the last 5 million years). Thus, rather than the endemic fauna consisting of long-isolated "prehistoric" species, these frogs are fairly recent immigrants that have quickly adapted to harsh - and drastically different - summit conditions and climate. The resulting publication from this research was a significant contribution in changing the paradigm of the Lost World. Now that we know that summit populations share recent evolutionary history with the surrounding midlands and lowlands, future conservation efforts should shift their focus away from only protecting highlands. 2. Are extreme landscape features restricting the movement of populations of frogs? Tepuis often have drastic landscape features such as 1000-3000ft walls (cliffs), many crevices and/or sinkholes of 100-1000ft in depth, large areas of barren rocks, and almost no permanent bodies of water. The summits are also drastically different in climate and soil composition from the surrounding lowlands. We can think of two main reasons (hypotheses) to explain why there are so many unique species atop these summits. Even though the summits are not completely isolated (since frogs arrived there long after tepui formation), can tepuis still be considered topographic or ecological islands in the sky? The cliffs and drastic changes in altitude as well as barren summit landscapes (little vegetation cover) may be extreme enough to partially yet significantly isolate populations atop the different summits. This barrier to their movement (i.e. barrier to gene flow) among populations on different summits would indicate that these topographic features may be responsible for the high endemicity atop the summits. However, it is also possible that the extreme climate difference and thus physiological constraints to tolerate these very different climates is what drives summit species to diverge quickly from lowland relatives. Thus, the isolation among summit populations should be more closely related to climate differences than to topographic complexity. Our two focus species were Tepuihyla edelcae, a tadpole pond breeder, and Stefania ginesi, a marsupial frog that carriers froglets until maturity. They are both restricted endemics atop the Chimantá Massif (a formation which encompasses many different tepui summits). We found much higher isolation among populations of the marsupial frog atop different summits, suggesting that certain breeding forms may be more sensitive to geography than others. However, in spite of the very low levels of divergence in the tadpole breeder, Tepuihyla edelcae, we still found strong signatures of among-summit isolation, suggesting that landscape is an important contributor to genetic isolation and thus may be responsible for the high endemicity atop these tepui summits. In conclusion, our study revealed that the Lost World of South America has recent immigrants to its very ancient summits, contrary to what was originally thought. However, even though the summits are not completely isolated, the complex landscape of walls and crevices still impedes movements of populations, and thus contributes to the partial isolation of this sky island ecosystem.
