Search

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 1000 m 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 support 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. [ABSTRACT FROM AUTHOR]

In 1947, when Thor Heyerdahl's Kon-Tiki hit ground in the Tuamotu archipelago, 102 days and ~4,000 km from its point of origin in South America, he inadvertently provided support for one of the most remarkable hypotheses of vertebrate dispersal. Iguanid lizards and boine snakes are ancient Gondwanan lineages whose distribution has been demonstrated to have been influenced by continental drift. Their enigmatic presence on the islands of the Pacific, however, has drawn fantastical conclusions of more than 8,000-km rafting from the Americas. We reexamine the hypothesis of dispersal in light of new molecular data and divergence time estimates. Our results suggest an early Paleogene (50-60 million years) divergence of these groups and the plausibility of an Asiatic or Australian (over land) source. Because the subfossil record indicates that iguanas (but not snakes) were a primary food source of island inhabitants, the absence of these species from islands with a longer history of human presence is unsurprising. Together these findings are taken as evidence of the influence humans have had on these taxa and are put forth as an example of anthropogenic obfuscation of biogeographic history. We suggest that this history is one of terrestrial connections permitting the colonization of the islands of the Pacific. [ABSTRACT FROM AUTHOR]

Abstract: Inferring the evolutionary and biogeographic history of taxa occurring in a particular region is one way to determine the processes by which the biodiversity of that region originated. Tree boas of the genus Corallus are an ancient clade and occur throughout Central and South America and the Lesser Antilles, making it an excellent group for investigating Neotropical biogeography. Using sequenced portions of two mitochondrial and three nuclear loci for individuals of all recognized species of Corallus, we infer phylogenetic relationships, present the first molecular analysis of the phylogenetic placement of the enigmatic C. cropanii, develop a time-calibrated phylogeny, and explore the biogeographic history of the genus. We found that Corallus diversified within mainland South America, via over-water dispersals to the Lesser Antilles and Central America, and via the traditionally recognized Panamanian land bridge. Divergence time estimates reject the South American Caribbean-Track as a general biogeographic model for Corallus and implicate a role for events during the Oligocene and Miocene in diversification such as marine incursions and the uplift of the Andes. Our findings also suggest that recognition of the island endemic species, C. grenadensis and C. cookii, is questionable as they are nested within the widely distributed species, C. hortulanus. Our results highlight the importance of using widespread taxa when forming and testing biogeographic hypotheses in complex regions and further illustrate the difficulty of forming broadly applicable hypotheses regarding patterns of diversification in the Neotropical region. [Copyright &y& Elsevier]