Karyological Characterization of the Endemic Iberian Rock Lizard, Iberolacerta Monticola (Squamata, Lacertidae): Insights into Sex Chromosome Evolution

[Abstract] Rock lizards of the genus Iberolacerta constitute a promising model to examine the process of sex chromosome evolution, as these closely related taxa exhibit remarkable diversity in the degree of sex chromosome differentiation with no clear phylogenetic segregation, ranging from cryptic to highly heteromorphic ZW chromosomes and even multiple chromosome systems (Z1Z1Z2Z2/Z1Z2W). To gain a deeper insight into the patterns of karyotype and sex chromosome evolution, we performed a cytogenetic analysis based on conventional staining, banding techniques and fluorescence in situ hybridization in the species I. monticola, for which previous cytogenetic investigations did not detect differentiated sex chromosomes. The karyotype is composed of 2n = 36 acrocentric chromosomes. NORs and the major ribosomal genes were located in the subtelomeric region of chromosome pair 6. Hybridization signals of the telomeric sequences (TTAGGG)n were visualized at the telomeres of all chromosomes and interstitially in 5 chromosome pairs. C-banding showed constitutive heterochromatin at the centromeres of all chromosomes, as well as clear pericentromeric and light telomeric C-bands in several chromosome pairs. These results highlight some chromosomal markers which can be useful to identify species specific diagnostic characters, although they may not accurately reflect the phylogenetic relationships among the taxa. In addition, C-banding revealed the presence of a heteromorphic ZW sex chromosome pair, where W is smaller than Z and almost completely heterochromatic. This finding sheds light on sex chromosome evolution in the genus Iberolacerta and suggests that further comparative cytogenetic analyses are needed to understand the processes underlying the origin, differentiation and plasticity of sex chromosome systems in lacertid lizards.Xunta de Galicia; PGIDIT03RFO10301PRXunta de Galicia; PGIDIT06RFO10301PRItalia. Ministero dell'istruzione, dell'università e della ricerca; PRIN 200

Molecular and cytogenetic characterisation of repetitive DNAs in squamate reptiles (Lacertidae)

Caratterizzazione citogenetica e molecolare di DNA satelliti nei rettili squamati (Lacertidae). La posizione dei rettili nella filogenesi degli amnioti rende lo studio del loro genoma cruciale per comprendere l’evoluzione genomica degli amnioti stessi. I DNA satelliti costituiscono una significativa porzione del genoma degli eucarioti, e sono una delle cause della variabilità delle dimensioni del loro genoma. Scopo di questa ricerca è stato quello di isolare e caratterizzare due differenti DNA satelliti (HindIII e TaqI) dal genoma di vari lacertidi. Un primo risultato indica che HindIII è presente in tutte le specie di Iberolacerta, ha un tasso evolutivo circa dieci volte più veloce di TaqI che si trova in posizione pericentromerica/interstiziale, in un numero minore di cromosomi ed è rappresentato nel genoma di tutti lacertidi studiati. Inoltre, approfondendo lo studio dell’evoluzione di questi due DNA satelliti nelle otto specie di Iberolacerta abbiamo osservato che entrambi i DNA satelliti mostrano modelli evolutivi complessi e disparati, e un comportamento altamente dinamico che può essere correlato con i cambiamenti cromosomici e la varietà cariotipica tipici di questo genere. Infine, abbiamo osservato che in Lacerta il satellite TaqI è coinvolto nella differenziazione per eterocromatinizzazione del cromosoma W. È interessante notare che nelle specie di Lacerta studiate le ripetizioni TaqI si dividono in due gruppi: uno contenente ripetizioni W-specifiche, l’altro ripetizioni autosoma-specifiche. Inoltre, la presenza di TaqI sul W delle specie di Lacerta studiate supporta l'omologia dei cromosomi sessuali in queste specie. Infatti, sembra improbabile che le stesse ripetizioni si siano accumulate sul W di specie diverse solo per effetto del caso. È invece probabile che questo satellite sia rimasto intrappolato sul W dell'antenato comune delle moderne specie di Lacerta. Infine, la presenza di TaqI sul W di Lacerta e l’assenza sul W di tutte le altre specie studiate sembra sostenere il monofiletismo di questo genere

Molecular and cytogenetic characterisation of repetitive DNAs in squamate reptiles (Lacertidae)

La posizione dei rettili nella filogenesi degli amnioti rende lo studio del loro genoma cruciale per comprendere l’evoluzione genomica degli amnioti stessi. I DNA satelliti costituiscono una significativa porzione del genoma degli eucarioti, e sono una delle cause della variabilità delle dimensioni del loro genoma. Scopo di questa ricerca è stato quello di isolare e caratterizzare due differenti DNA satelliti (HindIII e TaqI) dal genoma di vari lacertidi. Un primo risultato indica che HindIII è presente in tutte le specie di Iberolacerta, ha un tasso evolutivo circa dieci volte più veloce di TaqI che si trova in posizione pericentromerica/interstiziale, in un numero minore di cromosomi ed è rappresentato nel genoma di tutti lacertidi studiati. Inoltre, approfondendo lo studio dell’evoluzione di questi due DNA satelliti nelle otto specie di Iberolacerta abbiamo osservato che entrambi i DNA satelliti mostrano modelli evolutivi complessi e disparati, e un comportamento altamente dinamico che può essere correlato con i cambiamenti cromosomici e la varietà cariotipica tipici di questo genere. Infine, abbiamo osservato che in Lacerta il satellite TaqI è coinvolto nella differenziazione per eterocromatinizzazione del cromosoma W. È interessante notare che nelle specie di Lacerta studiate le ripetizioni TaqI si dividono in due gruppi: uno contenente ripetizioni W-specifiche, l’altro ripetizioni autosoma-specifiche. Inoltre, la presenza di TaqI sul W delle specie di Lacerta studiate supporta l'omologia dei cromosomi sessuali in queste specie. Infatti, sembra improbabile che le stesse ripetizioni si siano accumulate sul W di specie diverse solo per effetto del caso. È invece probabile che questo satellite sia rimasto intrappolato sul W dell'antenato comune delle moderne specie di Lacerta. Infine, la presenza di TaqI sul W di Lacerta e l’assenza sul W di tutte le altre specie studiate sembra sostenere il monofiletismo di questo genere.Reptiles are the stem group to birds and mammals, and the study of reptile genome is critical for understanding genome evolution in amniotes. Despite the ample literature dealing with satellite DNA (satDNA) in eukaryotes, there are few studies in reptiles. The aim of this research was to isolate and characterize two different satDNAs (HindIII and TaqI) from several lacertid species. Firstly, we found that these satDNAs seem to evolve at different rates in the studied lizards, with HindIII showing a tenfold faster evolutionary rate than TaqI. Indeed, it should be noted that HindIII repeats are centromerically located on all the acrocentric chromosomes of Iberolacerta. Conversely, TaqI repeats are pericentromerically located on a lower number of chromosomes in the species here analysed. Secondly, we explored the mode of evolution of two satDNA families shared by all eight Iberolacerta species. Both satDNAs showed complex and disparate evolutionary patterns, and a highly dynamic behaviour which may be correlated with chromosomal changes and karyotype diversification in this genus. Finally, we found that in Lacerta, TaqI satDNA is involved in the differentiation of the W sex chromosome by heterochromatinization. Interestingly, in Lacerta species TaqI satDNA repeats are differentiated in two groups, one containing W-specific repeats and the other repeats that occur on autosomes. Furthermore, the sharing of TaqI repeats by the W of the Lacerta species investigated seems to indicate the homology of sex chromosomes among these species. Indeed, it would be improbable that the same repeats accumulated on the W chromosome of different species as result of a random process. In contrast, it is likely that these repeats were trapped in the heterochromosome of the common ancestor of modern Lacerta species. The sharing of repetitive elements on the W by Lacerta species and their absence on the W of all the other species investigated also support the monophyletism of this genus

Genome Duplication in Early Vertebrates: Insights from Agnathan Cytogenetics

Agnathans represent a remnant of a primitive offshoot of the vertebrates, and the long evolutionary separation between their 2 living groups, namely hagfishes and lampreys, could explain profound biological differences, also in karyotypes and genome sizes. Here, cytogenetic studies available on these vertebrates were summarized and data discussed with reference to the recently demonstrated monophyly of this group and to the 2 events of whole genome duplication (1R and 2R) characterizing the evolution of vertebrates. The comparison of cytogenetic data and phylogenetic relationships among agnathans and gnathostomes seems to support the hypothesis that 1R and 2R occurred before the evolutionary divergence between jawless and jawed vertebrates

Isolation of novel microsatellite loci in the black goby Gobius niger and cross-amplification in other gobiid species (Perciformes, Gobiidae)

Twelve microsatellite loci were isolated from and characterized for the black goby Gobius niger. These loci were tested on a total of 48 individuals from two geographically distant locations (Orbetello and Cattolica) and the number of alleles ranged from two to 18, with expected (He) and observed (Ho) heterozygosities ranging from 0·042 to 0·941 and from 0·042 to 0·917, respectively. The loci described were used to cross-amplify other gobiid species belonging to Gobius,Zosterisessor, Lesueurigobius and Aphia

The role of life-history traits, selective pressure and hydrographic boundaries in shaping the genetic structure of the transparent goby, Aphia minuta

The transparent goby (Aphia minuta) is a small progenetic goby that displays a short life cycle with early reproductive maturity and represents a valuable fishery resource harvested by artisanal fleets in most part of its distributional range. This study aimed to define the genetic variability in A. minuta at five sampling sites within the Mediterranean Sea and one in the Atlantic Ocean through the analysis of 11 nuclear microsatellite loci. The results revealed that several genetic diversity estimators (expected and observed heterozygosities, mean number of alleles and allelic richness) were lower in the Atlantic Ocean than in the Mediterranean Sea, suggesting the role of past or current demographic events in shaping this pattern. The genetic structure was investigated using both classical genetic differentiation descriptors and Bayesian approaches, and by defining the current and past migration rates. The results obtained revealed a pronounced genetic structure within the Mediterranean Sea and suggest a very low current migration rate. The pattern of historical migration suggests the possible role of hydrographic boundaries in shaping the genetic structure detected in this species. In addition, the identification of loci under selection suggests the possible implication of selective pressures that are acting on genes connected with the peculiar life cycle of this gobiid fish

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