Canvi evolutiu dels lacèrtids de la Mediterrània occidentalestimes en el genoma nuclear

Abstract

Introduction This thesis comprises part of a wider project that addresses the evolution of Mediterranean lizards of the genus Podarcis (Wagler, 1830), and is mainly focused on insular populations. This genus is widespread across the Mediterranean basin. They exhibit a great intraspecific variability in morphological traits. In particular, melanic and non-melanic populations (which are completely green or brown, and/or with intermediate coloration) are found on different islands. The causes for this variability remain unknown. The Podarcis genus contains various insular endemism such as Podarcis tiliguerta from Corsica and Sardinia islands, and P. lilfordi and P. pityusensis from the Balearic archipelago. The Mediterranean basin is considered a biodiversity hotspot due to the presence of an exceptional number of endemic species and Podarcis provides an important component of this biodiversity. It can provide information on the effects of fragmentation and/or degradation of habitat. Analyses of Podarcis also have important implications for conservation of the group itself: understanding the evolutionary framework provides a basis for future conservation actions. Aim and results The present thesis is focused on the molecular study of the evolution of several Mediterranean Podarcis. It aims to build on and extend previous studies that made evolutionary inferences from just the mitochondrial DNA. This is achieved by analysing several nuclear markers (MC1R, RAG1, APOBE28, BLC9L, KIAA2018 and KIF24) in combination with mtDNA data. The main aim is to address two important evolutionary questions: i) Factors determining melanism in insular populations P. lilfordi and P. pityusensis present an important colour variation and polymorphism in the MC1R gene has been related to pigmentation in other species. Therefore, the relationship between DNA substitutions and melanism in different populations was studied. We did not detect any differences in the MC1R sequence that we analysed and so this sequence does not appear to be the basis of the colour variation in these Balearic Podarcis. Differences in gene expression were also compared between melanic and non-melanic individuals, but no differences that were directly related to MC1R expression were detected. Nevertheless, the transcriptome profiles of melanic and non-melanic individuals from two populations of P. lilfordi did show some differences. The main differences found between the two groups were: non-melanic samples showed over-expression of stress-response genes, while melanic individuals had higher metabolic rates and an increased inflammatory response to exogenous antigens. Despite finding differences in expression, our study was unable to reveal major insights into the genetic basis of melanism in these island lizards. ii) Phylogeny and phylogeography of different endemic species. This work contributes important findings relevant to the systematics and evolution of the species P. tiliguerta endemic to Corsica and Sardina. Using Bayesian phylogenetic dating, we determined that this species originated ~11 Ma ago. Both markers (nuclear genes and mtDNA) showed a high level of intraspecific divergence, especially between Corsica and Sardinia. Ancient divergence (which was estimated at 9.5 Ma ago) and associated high levels of between-island lineage sorting in nuclear markers support the view that Corsican and Sardinian populations should be recognized as two different species. Podarcis were also studied from the Columbretes archipelago, a small island group off the coast east of Spain. Populations were previously recognized as a subspecies of P. hispanica or as P. atrata species. However, the suitability of this taxonomic designation has been made unclear by recent systematics studies of Podarcis that have led to major taxonomic changes. We used nuclear and mitochondrial genes to define their phylogenetic relationships. Columbretes populations were found to be most closely related to the new taxon P. liolepis.