By David Coppage

Isolated table mountains with sheer cliffs in South America should be natural laboratories for evolution.  Why aren’t they?

The pantepui region spanning northern Brazil and parts of Venezuela and Guyana contains some of the most isolated ecological environments on earth.  The table mountains (tepui) are so remote and difficult to reach, some have been less visited than the moon.  Because of their sheer cliffs 1000 meters on all sides, evolutionists expected the habitats to be natural laboratories for evolution, because organisms managing to eke out a living on top of one tepui would be prevented from sharing genes with those on others.  Since the sandstone is said to be 1.5 billion years old, there has been ample time for the animals on top to evolve and diverge from one another in isolation.  Time estimates for the isolation of the tepui go back to the Cretaceous.

With this “ideal nursery of speciation” tempting scientists to look for tens or possibly hundreds of millions of years of evolution on these natural laboratories, an international team undertook the arduous task of visiting 17 tepui and collecting samples from amphibians and reptiles to compare their genes.  They expected differences; after all, “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.”  And outwardly, “Some of the lowest genetic distances are observed for populations that are currently recognized as distinct species and show striking phenotypic differences,” they said.  Their paper was published this week in Current Biology.1

Substantial diversity was the expectation based on the amount of time these creatures are believed to have been isolated.  But when they made the “analyses of two mitochondrial gene fragments evolving at different rates,” they were very surprised: “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).”  Many of the differences were less than 1%.  “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.”….

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