The evolution of viviparity in squamates has been the focus of much scientific attention in previous years. In particular, the possibility of the transition from viviparity back to oviparity has been the subject of a vigorous debate. Some studies have suggested this reversal is more frequent than previously thought. However, none of them provide conclusive evidence. We investigated this problem by studying the phylogenetic relationships between oviparous and viviparous lineages of the reproductively bimodal lizard species Zootoca vivipara . Our results show that viviparous populations are not monophyletic, and that several evolutionary transitions in parity mode have occurred. The most parsimonious scenario involves a single origin of viviparity followed by a reversal back to oviparity. This is the first study with a strongly supported phylogenetic framework supporting a transition from viviparity to oviparity.

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The concept of the oviparity-viviparity continuum refers to the wide range in the length of intrauterine egg retention and, hence, in the stage of embryonic development at oviposition existing in squamates. The evolutionary process underlying this continuum may involve not only a lengthening of egg retention in utero, but also a marked reduction in the thickness of the eggshell. The idea that there may exist a negative correlation between the developmental stage reached by the embryo at oviposition and the eggshell thickness within squamates, although supported by the comparison of oviparous vs. viviparous species, has seldom been evaluated by comparing eggshell thickness of oviparous forms with different lengths of intrauterine egg retention. Eggs of two distinct oviparous clades of the lizard Lacerta vivipara were compared. The eggs laid by females from Slovenian and Italian populations have thicker eggshells, contain embryos on average less developed at the time of oviposition, and require a longer incubation period before hatching than the eggs laid by females from French oviparous populations. Our data and several other examples available from the literature support the idea that the lengthening of intrauterine retention of eggs and the shortening of the subsequent external incubation of eggs are associated with reduction in the thickness of the eggshell, at least in some lineages of oviparous squamates. The current hypotheses that may account for this correlation are presented and a few restrictions and refinements to those hypotheses are discussed. In particular, other changes, such as increased vascularization of the oviduct and of the extraembryonic membranes, may play the same role as the decrease of eggshell thickness in facilitating prolonged intrauterine egg retention in squamates. Future studies should also consider the hypothesis that the length of intrauterine retention might directly depend on the extent of maternal-fetal chemical communication through the eggshell barrier.

Recent genetic works have suggested that the Iberian wall lizard Podarcis hispanicus (Steindachner, 1870) sensu lato is a species complex. Several forms have already been elevated to species rank and linked to available nomina, but at least three still have to be formally named, including the western Iberian forms currently designated as Podarcis hispanicus "type 1A", "type 1B" and "type 2". The aim of the present work is to assign a valid nomen to these taxa. Using multivariate analyses, we first checked that the morphological differences reported in Portugal between type 1 and type 2 are maintained over their distribution range. We then investigated phenotypic differentiation between type 1A and type 1B, which were found to be so similar that identification based on phenotype is currently not advisable. We propose to treat type 1 and type 2 as distinct species because of their level of genetic and phenotypic divergence, large area of distribution and ample evidence for reduced or absent introgression in contact zones. We maintain type 1A and 1B as subspecies for the time being, pending further analyses of their contact zone. The valid nomen for "Podarcis hispanica type 1 (sensu lato)" is Lacerta muralis guadarramae Boscá, 1916 which becomes Podarcis guadarramae (Boscá, 1916). Lineage type 1A is here described as a new taxon: P. guadarramae lusitanicus ssp. nov., inhabiting northern Portugal and northwestern Spain. The type 1B lineage corresponds to the nominotypical subspecies that inhabits Spain, mostly the Central Iberian Mountains. We were unable to locate an available nomen for "Podarcis hispanica type 2", which is here described as Podarcis virescens sp. nov. This species is widely distributed in the plains and plateaus of central and parts of south-western Spain as well as central and southern Portugal.