Evolution of Karyotypes in Chameleons.

The reconstruction of the evolutionary dynamics of karyotypes and sex determining systems in squamate reptiles is precluded by the lack of data in many groups including most chameleons (Squamata: Acrodonta: Chamaeleonidae). We performed cytogenetic analysis in 16 species of chameleons from 8 genera covering the phylogenetic diversity of the family and also phylogenetic reconstruction of karyotype evolution in this group. In comparison to other squamates, chameleons demonstrate rather variable karyotypes, differing in chromosome number, morphology and presence of interstitial telomeric signal (ITS). On the other hand, the location of rDNA is quite conserved among chameleon species. Phylogenetic analysis combining our new results and previously published data tentatively suggests that the ancestral chromosome number for chameleons is 2n = 36, which is the same as assumed for other lineages of the clade Iguania, i.e., agamids and iguanas. In general, we observed a tendency for the reduction of chromosome number during the evolution of chameleons, however, in Rieppeleon brevicaudatus, we uncovered a chromosome number of 2n = 62, very unusual among squamates, originating from a number of chromosome splits. Despite the presence of the highly differentiated ZZ/ZW sex chromosomes in the genus Furcifer, we did not detect any unequivocal sexual differences in the karyotypes of any other studied species of chameleons tested using differential staining and comparative genomic hybridization, suggesting that sex chromosomes in most chameleons are only poorly differentiated.

Sequence analysis and mapping of the Sry gene in species of the subfamily Arvicolinae (rodentia).

The rodent subfamily Arvicolinae, which contains about 125 species, presents some interesting exceptions concerning Sry, the sex determining gene in mammals. In some species multiple Sry copies have been described on the Y chromosome and in the Iberian vole, Microtus cabrerae, several Sry sequences have been cloned and mapped not only on the Y but also on the X chromosome. Here we present a comparative analysis of Sry sequences from a total of 22 species. Our study demonstrates for the first time that for most North American species, as previously reported for the European species, multiple copies of the Sry gene exist on the Y chromosome. Furthermore, we have sequenced and analyzed the full sequence of Sry from several European species, showing that the sequence and structure of the gene in this group of species present the main features described for Sry in other mammals. Finally, FISH analyses on some of these species demonstrated that all Sry sequences, despite their functional status, mapped on the euchromatic short arm of the Y chromosome.