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The process of speciation is often equated to the acquisition of reproductive isolation. This is a process typically envisioned as being correlated to divergence time: as time progresses the more likely it will be for diverging taxa to experience restrictions to gene exchange. This correlation has been tested and verified in a wide range of taxa; however, other aspects of differentiation, such as ecological divergence, have also been shown to correlate with reproductive isolation independently of divergence time or genomic differentiation. Characterizing reproductive isolation in multiple pairs of closely related taxa that are in different stages of the divergence process is a way of addressing these questions and disentangling the factors are more importante as engines of reproductive isolation. Wall lizards of genus Podarcis, particularly those belonging to the Iberian and North African group, are an appropriate model for this type of evaluations since they comprise various differentiated species with that establish a variety of natural contact zones. In this study we sampled and characterized patterns of hybridization in 9 contact zones between different species pairs using RADseq data. We found a generally low proportion of hybrids and contact zones were strongly bimodal in all cases, but with measurable differences in levels of gene flow among contact zones. Using data available from previous studies on this complex and in a multivariate statistical framework, we compared the level of hybridisation in each contact zone with several predictor variables: nuclear and mitochondrial genetic divergence, distribution overlap, and morphological, ecological and physiological distances between species. Our results show that, despite the general trend in other taxa, the level of hybridization in Podarcis contact zones does not seem to be correlated to divergence time. We discuss how other mechanisms may have influenced this pattern.

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Niche divergence among closely related lineages can be informative on the ecological and evolutionary processes involved in differentiation, particularly in the case of cryptic species complexes. Here we compared phylogenetic relationships and niche similarity between pairs of lineages included in the Podarcis hispanicus complex to examine patterns of niche divergence and its role in the organization of current diversity patterns, as allopatric, parapatric, and sympatric lineages occur in the Western Mediterranean Basin. First, we used ecological niche models to characterize the realized climatic niche of each Podarcis hispanicus complex lineage based on topographic and climatic variables, to identify important variables, and to test for niche conservatism or divergence between pairs of lineages. Variables related to precipitation generally exhibited the highest contribution to niche models, highlighting the importance of rainfall levels in shaping distributions of Podarcis wall lizards. We found that most forms have significant differences in realized climatic niches that do not follow the pattern of mitochondrial divergence. These results lend support to the hypothesis that genetic divergence across Podarcis hispanicus complex most likely occurred in allopatric conditions, mostly with significant niche divergence. Competition after secondary contact is also suggested by the common occurrence of niche overlap between lineages that exhibit strictly parapatric distribution. The almost continuous distribution of Podarcis lizards in the study area appears to be a result of a combination of complementary suitable niches and competition, which seem two important mechanisms limiting geographic distributions and restricting the existence of extensive contact zones.

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Evolutionary inference based on molecular phylogenetic methods has profoundly modified the way that we understand biological diversity, unravelling a higher evolutionary diversity than previously considered. An exemplary case of this is the group of Iberian and North African Podarcis wall lizards. More investigated than any other reptile group in Europe, the Podarcis hispanica species complex comprises unexpectedly high levels of phylogenetic diversity and illustrates how the discovery of further cryptic diversity may entangle evolutionary inference. In the present study, we report on the discovery of two new mitochondrial lineages in this species complex, reassess the phylogeny of the group, infer the age of major phylogenetic splits, and provide a detailed description of the geographical distributions of all known mitochondrial DNA lineages. Our data show that the differentiation of major lineages is older than previously considered, in most cases predating the Messinian salinity crisis. The new lineages discovered and their position in the phylogeny of the group profoundly modify previous biogeographical scenarios, clearly showing that the area today corresponding to the south-eastern corner of the Iberian Peninsula is a very important centre of diversification. The dating obtained for the differentiation of the lineages currently inhabiting this area coincides with the complex geological events that took place during the Miocene/Pleistocene transition, supporting the idea that both land movements and dramatic climatic oscillations during that period could be involved. Finally, the discovery of these new lineages, together with the observed distribution patterns, not only further augments the uncertainty associated to our understanding of the evolutionary history of this group of lizards, but also points to new areas of interest for future investigation.