Abstract
To understand the origin of Pantepui montane biotas, we studied the biogeography of toucanets in the genus Aulacorhynchus. These birds are ideal for analyzing historical relationships among Neotropical montane regions, given their geographic distribution from Mexico south to Bolivia, including northern Venezuela (Cordillera de la Costa), and the Pantepui. Analyses were based on molecular phylogenies using mitochondrial and nuclear DNA sequences. Topology tests were applied to compare alternative hypotheses that may explain the current distribution of Aulacorhynchus toucanets, in the context of previous hypotheses of the origin of Pantepui montane biotas. Biogeographic reconstructions in RASP and Lagrange were used to estimate the ancestral area of the genus, and an analysis in BEAST was used to estimate a time framework for its diversification. A sister relationship between the Pantepui and Andes+Cordillera de la Costa was significantly more likely than topologies indicating other hypothesis for the origin of Pantepui populations. The Andes was inferred as the ancestral area for Aulacorhynchus, and the group has diversified since the late Miocene. The biogeographic patterns found herein, in which the Andes are the source for biotas of other regions, are consistent with those found for flowerpiercers and tanagers, and do not support the hypothesis of the geologically old Pantepui as a source of Neotropical montain diversity. Based on the high potential for cryptic speciation and isolation of Pantepui populations, we consider that phylogenetic studies of additional taxa are important from a conservation perspective.
Highlights
Given their old geological origin, geographic isolation, and endemic biota, the highlands of the Guianan Shield have been a source of inspiration for explorers and naturalists alike
The Bayesian binary Markov chain Monte Carlo (MCMC) analysis in RASP and the likelihood Dispersal-Extinction-Cladogenesis model (DEC) analysis in Lagrange produced different results regarding the ancestral area of Aulacorhynchus (Figure 3)
The analysis indicates that all currently recognized species likely originated prior to the Pleistocene, with one exception: A. sulcatus and A. derbianus split at some time between the mid Pliocene and the early Pleistocene (95% highest posterior density (HPD) = 3.6–1.6 million years ago (Mya))
Summary
Given their old geological origin, geographic isolation, and endemic biota, the highlands of the Guianan Shield have been a source of inspiration for explorers and naturalists alike This biogeographic region, known as ‘Pantepui’ [1], [2], is formed by mountains derived from the Precambrian sandstone rocks of the Roraima Group in southern Venezuela, western Guyana, and northern Brazil [3]. The ancient age of the Pantepui has long been associated with the notion of undisturbed and continuous processes of biological diversification and isolation [5], [6] This idea, known as the Plateau Theory, proposes that the ‘Pantepui fauna is the remnant of a fauna formerly widespread on a plateau dissected by erosion into separate tepuis’ [1]. Palaeoecological studies based on Quaternary sediments indicate vertical displacement of vegetation in the middle and lower elevations of these table mountains [6]
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