Background: Mitochondrial markers are widely used as a first approach in determining evolutionary relationships among vertebrate taxa at different hierarchical scales. Cytochrome b and cytochrome oxidase I are among the most common markers; they are particularly useful in phylogeography and species delineation studies. Simulation and empirical studies show that increasing the taxon sampling has a clear and strong effect on the accuracy of the inferred trees and therefore on hypothesized phylogenetic relationships (and eventually in new taxonomic rearrangements); this should be considered in the design of studies. The lizard genus Liolaemus is widely distributed in southern South America and includes more than 250 described species. The number of taxa and the distribution of Liolaemus species/populations makes them a good model for testing different hypotheses in systematics. Methods: We studied two Liolaemus species, Liolaemus nigroviridis and L. monticola as focal species to evaluate their monophyly and the influence of adding new samples from related taxa in the resulting phylogenies. We performed phylogenetic analyses (maximum likelihood and Bayesian inference) using 141 sequences of the mitochondrial DNA Cytochrome b (cyt-b) of 11 Liolaemus species. Results: Our study show that using intensive taxon sampling for phylogenetic reconstructions, two species (L. uniformis and L. nitidus) are placed within the clades of the two focal species (L. nigroviridis and L. monticola, respectively). Conclusions: Our study confirms the importance of taxon sampling to infer more accurate phylogenetic relationships, particularly to reveal hidden polyphyly or paraphyly, which may have a strong impact on taxonomic proposals and/or inferring cryptic diversity.

Mepraia is a genus (Triatominae) endemic to Chile and a vector of Trypanosoma cruzi. Alternative phylogeographic hypotheses have been suggested for Mepraia. We tested different colonization routes hypothesized using mitochondrial sequences and phylogeographic approaches to select the best-supported hypothesis. Our results suggest that, after the split from the sister genus Triatoma at ~4.3 Mya, Mepraia formed two main clades at ~2.1 Mya. The northern clade diverged from Mepraia sp. ~1.7 Mya, giving rise to M. parapatrica and M. gajardoi about ~1.4 Mya. The southern clade originated M. spinolai ~1.68 Mya. We suggest that Mepraia had an origin in the north-central Andes along with orogenic processes, reinforced by hyperaridity during the Pliocene. The hyperarid cycle would have separated the southern and northern clades. Then, in the northern clade, dispersal occurred north and south from the centre through corridors during the Pleistocene Climatic Oscillations. Climate changes may have induced a major speciation process in the Atacama Desert, while the more homogeneous habitat colonized by the southern clade led to only one, but structured, species.

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