Isolation and characterization of two satellite DNAs in Atlantolacerta andreanskyi (Werner, 1929) (Reptilia, Lacertidae).

Two satellite DNAs (satDNAs) have been isolated and characterized from three populations of Atlantolacerta andreanskyi. One satDNA (AAN-TaqI) has been isolated here from the first time. It is characterized by a tendency to AT enrichment (AT = 54.2%) and monomer length ranging from 187 to 199 bp. FISH experiments showed that this element occurs in subterminal position on the short arms of all chromosomes of the complement. The analyses of genetic variability of AAN-TaqI showed that the concerted evolution is acting effectively on these repeats that form separate clusters consistent with the geographic origin in the phylogenetic tree, thus supporting the hypothesis that A. andreanskyi would be a species complex. In addition, in the population from Jbel Aoulime this satDNA is already differentiated into two subfamilies. The other satDNA belongs to the family of IMO-TaqI already isolated in other lacertids. Differently from AAN-TaqI, concerted evolution does not seem to act effectively on this element that is not differentiated between populations. These results confirm that IMO-TaqI (AT = 53.4%) is conserved in both chromosomal position and most of its sequence in the lacertids from which it has been characterized so far. Its remarkable evolutionary conservation for about 45 million years could indicate that this satDNA may have a functional role that future investigations could unveil. Once again, this study shows how satDNAs coexisting in the same genome may differ in their evolutionary pattern, even though the reasons underlying this phenomenon in the species here studied have still to be fully understood.

Characterization of a satellite DNA in the genera Lacerta and Timon (Reptilia, Lacertidae) and its role in the differentiation of the W chromosome.

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.

Cytogenetic Characterization of a Population of Acanthodactylus lineomaculatus Duméril and Bibron, 1839 (Reptilia, Lacertidae), from Southwestern Morocco and Insights into Sex Chromosome Evolution.

Acanthodactylus lineomaculatus is now regarded as an ecotype of A. erythrurus with which it has been recently synonymized. Despite the wide range of A. erythrurus, karyological data for this species are scarce and limited to classical cytogenetic studies carried out in individuals from only 2 locations (central Spain and Spanish enclave of Melilla on the northwestern Mediterranean Moroccan coast). Here, for the first time, we cytogenetically characterized individuals of A. lineomaculatus from the southwestern Moroccan Atlantic coast with the aim to increase the karyological knowledge of this wide-ranging species and to assess if any chromosomal changes can be found in this ecotype in comparison to other populations of this species. The diploid number of the individuals investigated is 2n = 38 which is typical of most lacertids. Active NORs were located telomerically in a medium-small pair of chromosomes, and no inactive NORs were detected. C-banding revealed an intensely heterochromatic W chromosome composed of AT-rich (centromere and long arm telomeric region) and GC-rich (most of the long arm) regions, with extended interstitial telomeric sequences. These telomere-like repeats occupy the GC-rich heterochromatin of the W. The DNA composition of the W represents a trait distinguishing A. lineomaculatus (southwestern Morocco) from A. erythrurus from Spain that possess a DAPI-positive (AT-rich) W chromosome. In conclusion, these results add further evidence to the remarkable karyotype conservation in lacertid lizards, although differences in NOR location and in W chromosome structure among populations could suggest an incipient speciation mediated by chromosome changes in this wide-ranging lizard species.

The Effects of Paleoclimatic Events on Mediterranean Trout: Preliminary Evidences from Ancient DNA.

In this pilot study for the first time, ancient DNA has been extracted from bone remains of Salmo trutta. These samples were from a stratigraphic succession located in a coastal cave of Calabria (southern Italy) inhabited by humans from upper Palaeolithic to historical times. Seven pairs of primers were used to PCR-amplify and sequence from 128 to 410 bp of the mtDNA control region of eleven samples. Three haplotypes were observed: two (ADcs-1 and MEcs-1) already described in rivers from the Italian peninsula; one (ATcs-33) belonging to the southern Atlantic clade of the AT Salmo trutta mtDNA lineage (sensu Bernatchez). The prehistoric occurrence of this latter haplotype in the water courses of the Italian peninsula has been detected for the first time in this study. Finally, we observed a correspondence between frequency of trout remains and variation in haplotype diversity that we related with ecological and demographic changes resulting from a period of rapid cooling known as the Younger Dryas.

Biocomplexity in Populations of European Anchovy in the Adriatic Sea.

The sustained exploitation of marine populations requires an understanding of a species' adaptive seascape so that populations can track environmental changes from short- and long-term climate cycles and from human development. The analysis of the distributions of genetic markers among populations, together with correlates of life-history and environmental variability, can provide insights into the extent of adaptive variation. Here, we examined genetic variability among populations of mature European anchovies (n = 531) in the Adriatic (13 samples) and Tyrrhenian seas (2 samples) with neutral and putative non-neutral microsatellite loci. These genetic markers failed to confirm the occurrence of two anchovy species in the Adriatic Sea, as previously postulated. However, we found fine-scale population structure in the Adriatic, especially in northern areas, that was associated with four of the 13 environmental variables tested. Geographic gradients in sea temperature, salinity and dissolved oxygen appear to drive adaptive differences in spawning time and early larval development among populations. Resolving adaptive seascapes in Adriatic anchovies provides a means to understand mechanisms underpinning local adaptation and a basis for optimizing exploitation strategies for sustainable harvests.

Coupling Demographic and Genetic Variability from Archived Collections of European Anchovy (Engraulis encrasicolus).

It is well known that temporal fluctuations in small populations deeply influence evolutionary potential. Less well known is whether fluctuations can influence the evolutionary potentials of species with large census sizes. Here, we estimated genetic population parameters from as survey of polymorphic microsatellite DNA loci in archived otoliths from Adriatic European anchovy (Engraulis encrasicolus), a fish with large census sizes that supports numerous local fisheries. Stocks have fluctuated greatly over the past few decades, and the Adriatic fishery collapsed in 1987. Our results show a significant reduction of mean genetic parameters as a consequence of the population collapse. In addition, estimates of effective population size (Ne) are much smaller than those expected in a fishes with large population census sizes (Nc). Estimates of Ne indicate low effective population sizes, even before the population collapse. The ratio Ne/Ne ranged between 10-6 and 10-8, indicating a large discrepancy between the anchovy gene pool and population census size. Therefore, anchovy populations may be more vulnerable to fishery effort and environmental change than previously thought.

Evolutionary dynamics of two satellite DNA families in rock lizards of the genus Iberolacerta (Squamata, Lacertidae): different histories but common traits.

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.

Isolation and characterization of two satellite DNAs in some Iberian rock lizards (Squamata, Lacertidae).

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.