Evaluating the phylogenetic signal limit from mitogenomes, slow evolving nuclear genes, and the concatenation approach. New insights into the Lacertini radiation using fast evolving nuclear genes and species trees.

Estimating the phylogeny of lacertid lizards, and particularly the tribe Lacertini has been challenging, possibly due to the fast radiation of this group resulting in a hard polytomy. However this is still an open question, as concatenated data primarily from mitochondrial markers have been used so far whereas in a recent phylogeny based on a compilation of these data within a squamate supermatrix the basal polytomy seems to be resolved. In this study, we estimate phylogenetic relationships between all Lacertini genera using for the first time DNA sequences from five fast evolving nuclear genes (acm4, mc1r, pdc, βfib and reln) and two mitochondrial genes (nd4 and 12S). We generated a total of 529 sequences from 88 species and used Maximum Likelihood and Bayesian Inference methods based on concatenated multilocus dataset as well as a coalescent-based species tree approach with the aim of (i) shedding light on the basal relationships of Lacertini (ii) assessing the monophyly of genera which were previously questioned, and (iii) discussing differences between estimates from this and previous studies based on different markers, and phylogenetic methods. Results uncovered (i) a new phylogenetic clade formed by the monotypic genera Archaeolacerta, Zootoca, Teira and Scelarcis; and (ii) support for the monophyly of the Algyroides clade, with two sister species pairs represented by western (A. marchi and A. fitzingeri) and eastern (A. nigropunctatus and A. moreoticus) lineages. In both cases the members of these groups show peculiar morphology and very different geographical distributions, suggesting that they are relictual groups that were once diverse and widespread. They probably originated about 11-13 million years ago during early events of speciation in the tribe, and the split between their members is estimated to be only slightly older. This scenario may explain why mitochondrial markers (possibly saturated at higher divergence levels) or slower nuclear markers used in previous studies (likely lacking enough phylogenetic signal) failed to recover these relationships. Finally, the phylogenetic position of most remaining genera was unresolved, corroborating the hypothesis of a hard polytomy in the Lacertini phylogeny due to a fast radiation. This is in agreement with all previous studies but in sharp contrast with a recent squamate megaphylogeny. We show that the supermatrix approach may provide high support for incorrect nodes that are not supported either by original sequence data or by new data from this study. This finding suggests caution when using megaphylogenies to integrate inter-generic relationships in comparative ecological and evolutionary studies.