A south-to-north biogeographic hypothesis for Andean speciation: evidence from the lizard genus Proctoporus (Reptilia, Gymnophthalmidae)
The lizard genus Proctoporus Tschudi, 1845 was used as a model to test the South-to-North Speciation Hypothesis (SNSH) for species groups occurring in the Andes Mountains of South America. This hypothesis proposes that speciation of high Andean taxa followed a south-to-north pattern, generally coinciding with the progression of final uplift of the Andes. According to SNSH, a phylogenetic hypothesis of relationships of a taxonomic group occurring in the high Andes would show a branching pattern in which the southernmost species diverged first, followed by the more northern species, and so on in a northerly pattern. Location
The central and northern Andes Mountains in South America. Methods
A phylogenetic hypothesis was reconstructed for all species of the lizard genus Proctoporus by examining the external morphology of 341 individuals. This phylogeny was then examined to determine monophyly of the genus, distribution patterns of species groups, and congruence with SNSH. Results
The genus Proctoporus did appear to be monophyletic and, therefore, it was valid to use this group to assess SNSH. The southernmost species were found to be the most basal, which was consistent with SNSH. The species occurring in the northern Andes did not exactly match the SNSH prediction. The Venezuelan and Trinidadian species did appear to be highly derived, as predicted by the hypothesis, but the Ecuadorian and Colombian species did not form a particular pattern in relation to the hypothesis. Main conclusions
The SNSH does appear to have predictive power with regard to large-scale distribution patterns. The finer-scale patterns of speciation in the Andes, however, appear to be a more complex phenomenon that cannot be fully explained by a simple hypothesis. It is important to have a testable hypothesis in hand with which to compare data from disparate species groups. The incorporation of phylogenetic data of other high Andean taxa with similar distribution patterns is necessary to determine the full utility of SNSH in explaining evolutionary patterns in the Andes of South America.