Squamate reptiles show a striking diversity in modes of sex determination, including both genetic (XY or ZW) and temperature-dependent sex determination systems. The genomes of only a handful of species have been sequenced, analyzed and assembled including the genome of Anolis carolinensis. Despite a high genome coverage, only macrochromosomes of A. carolinensis were assembled whereas the content of most microchromosomes remained unclear. Most of the Anolis species have homomorphic XY sex chromosome system. However, some species have large heteromorphic XY chromosomes (e.g., A. sagrei) and even multiple sex chromosomes systems (e.g. A. pogus), that were shown to be derived from fusions of the ancestral XY with microautosomes. We applied next generation sequencing of flow sorting-derived chromosome-specific DNA pools to characterize the content and composition of microchromosomes in A. carolinensis and A. sagrei. Comparative analysis of sequenced chromosome-specific DNA pools revealed that the A. sagrei XY sex chromosomes contain regions homologous to several microautosomes of A. carolinensis. We suggest that the sex chromosomes of A. sagrei are derived by fusions of the ancestral sex chromosome with three microautosomes and subsequent loss of some genetic content on the Y chromosome.

Anoles are a clade of iguanian lizards that underwent an extensive radiation between 125 and 65 million years ago. Their karyotypes show wide variation in diploid number spanning from 26 (Anolis evermanni) to 44 (A. insolitus). This chromosomal variation involves their sex chromosomes, ranging from simple systems (XX/XY), with heterochromosomes represented by either micro- or macrochromosomes, to multiple systems (XXXX/XXY). Here, for the first time, the homology relationships of sex chromosomes have been investigated in nine anole lizards at the whole chromosome level. Cross-species chromosome painting using sex chromosome paints from A. carolinensis, Ctenonotus pogus and Norops sagrei and gene mapping of X-linked genes demonstrated that the anole ancestral sex chromosome system constituted by microchromosomes is retained in all the species with the ancestral karyotype (2n = 36, 12 macro- and 24 microchromosomes). On the contrary, species with a derived karyotype, namely those belonging to genera Ctenonotus and Norops, show a series of rearrangements (fusions/fissions) involving autosomes/microchromosomes that led to the formation of their current sex chromosome systems. These results demonstrate that different autosomes were involved in translocations with sex chromosomes in closely related lineages of anole lizards and that several sequential microautosome/sex chromosome fusions lead to a remarkable increase in size of Norops sagrei sex chromosomes.

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The brown trout (Salmo trutta L.) is widely distributed all around Europe but its natural diversity is 19 threatened by massive stocking with Atlantic domestic strains. Describing the remaining natural genetic 20 diversity and the proportion of domestic hatchery strains in rivers is a prerequisite for smart conservation. 21 The high genetic diversity of brown trout populations around the Tyrrhenian Sea is well known. Use of 22 twelve microsatellites has allowed description of the natural genetic structure of populations and detection 23 of the consequences of stocking. Mitochondrial DNA control region sequences and the LDH-C1* gene 24 enabled placement of each population into one of the six mitochondrial and two allozymic known 25 2 evolutionary lineages. The Corsican populations showed low intra-population genetic diversity but an 26 exceptionally high level of inter-population differentiation. More southern Tyrrhenian regions exhibited 27 opposite pattern of diversity, partly due to the Atlantic domestic introgression. Globally, the natural 28 structure outlines two north-south clines: high inter-population differentiation and predominance of the 29 Adriatic lineage in the north, but lower inter-population differentiation and presence of the natural Atlantic 30 lineage in the south. In addition, the Tyrrhenian region is the contact zone between the widespread 31 Adriatic lineage and a local natural Atlantic lineage probably coming from North Africa through the Strait 32 of Gibraltar.

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In this study, IMO-TaqI satDNA, previously isolated in several species of Lacertidae, was isolated and characterized from four species of the genus Lacerta and three of the genus Timon. The aim was to gain further insights into the evolutionary dynamics of this satDNA, its occurrence among lacertids and to understand if it plays any role in sex chromosome evolution in these seven species. The results here obtained highlighted the presence of this repetitive element in the genome of all the species investigated, thus indicating that IMO-TaqI satDNA is evolutionary conserved among a wide variety of lacertids. In addition, this element was found to be very abundant in the constitutive heterochromatin of the W-sex chromosome of the four Lacerta species investigated. The occurrence of IMO-TaqI satDNA on Lacerta heterochromosome suggests that it is involved in the differentiation of the W chromosome by heterochromatinization, and the fact that it is absent in the W of other lacertids investigated seems to confirm that repetitive DNA sequences would remain randomly trapped into the sex chromosomes, undergoing amplification as a consequence of the suppression of recombination.

Satellite DNAs represent a large portion of all high eukaryotic genomes. They consist of numerous very similar repeated sequences, tandemly arranged in large clusters up to 100 million base pairs in length, usually located in the heterochromatic parts of chromosomes. The biological significance of satDNAs is still under discussion, but most of their proposed functions are related to heterochromatin and/or centromere formation and function. Because information about the structure of reptilian satDNA is far from exhaustive, we present a molecular and cytogenetic characterization of two satDNA families in four lacertid species. Two families of tandemly repeated DNAs, namely TaqI and HindIII satDNAs, have been cloned and sequenced from four species belonging to the genus Iberolacerta. These satDNAs are characterized by a monomer length of 171-188 and 170-172 bp, and by an AT content of 60.5% and 58.1%, respectively. FISH experiments with TaqI satDNA probe produced bright signals in pericentromeric regions of a subset of chromosomes whereas all the centromeres were marked by HindIII probe. The results obtained in this study suggest that chromosome location and abundance of satDNAs influence the evolution of these elements, with centromeric families evolving tenfold faster than interstitial/pericentromeric ones. Such different rates render different satellites useful for phylogenetic investigation at different taxonomic ranks.

Satellite DNAs compose a large portion of all higher eukaryotic genomes. The turnover of these highly repetitive sequences is an important element in genome organization and evolution. However, information about the structure and dynamics of reptilian satellite DNA is still scarce. Two satellite DNA families, HindIII and TaqI, have been previously characterized in four species of the genus Iberolacerta. These families showed different chromosomal locations, abundances, and evolutionary rates. Here, we extend the study of both satellite DNAs (satDNAs) to the remaining Iberolacerta species, with the aim to investigate the patterns of variability and factors influencing the evolution of these repetitive sequences. Our results revealed disparate patterns but also common traits in the evolutionary histories of these satellite families: (i) each satellite DNA is made up of a library of monomer variants or subfamilies shared by related species; (ii) species-specific profiles of satellite repeats are shaped by expansions and/or contractions of different variants from the library; (iii) different turnover rates, even among closely related species, result in great differences in overall sequence homogeneity and in concerted or non-concerted evolution patterns, which may not reflect the phylogenetic relationships among taxa. Contrasting turnover rates are possibly related to genomic constraints such as karyotype architecture and the interspersed organization of diverging repeat variants in satellite arrays. Moreover, rapid changes in copy number, especially in the centromeric HindIII satDNA, may have been associated with chromosomal rearrangements and even contributed to speciation within Iberolacerta.