Karyological Characterization of the Endemic Iberian Rock Lizard, <b><i>Iberolacerta monticola</i></b> (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.

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

“…The fact that the centromeric heterochromatin of A . lineomaculatus is stained by both DAPI and CMA 3 indicates that this heterochromatin probably does not contain DNA sequences particularly rich in AT or GC [for similar considerations, see Rojo et al, 2014]. An exception is represented by the W chromosome which is extremely GC-rich.…”

“…These variants may involve an increase in the number of microchromosomes, like in Takydromus sexlineatus . The lack of microchromosomes is observed, for example, in Zootoca vivipara and in species of the genus Iberolacerta [e.g., Odierna et al, 1996;Arribas et al, 2006;Rojo et al, 2014Rojo et al, , 2015. The presence of biarmed chromosomes has been reported in species of Timon , in Parvilacerta parva [Gorman, 1973], and in the Pyrenean species of Iberolacerta ( I. aranica , I. aurelioi , and I. bonnali ) [Odierna et al, 1996].…”

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

“…Fibroblast cell cultures were established from autotomized tail tips and cultured as reported by Rojo et al. (). Metaphase spreads were prepared according to Rens, Fu, O'Brien, and Ferguson‐Smith ().…”

Conservation of sex chromosomes in lacertid lizards

“…With the exception of several lineages with multiple neo‐sex chromosomes (Rojo et al . ; reviewed in Pokorná et al . ), the Z and W sex chromosomes are believed to be rather homomorphic and are only cytogenetically distinguishable by C‐banding detection of the notable heterochromatin accumulation on the W chromosomes (Olmo et al .…”