Chromosome evolution in a genus that deviates from the standard karyotype formula of Lacertidae

Abstract

This paper describes the preparation of flow-sorted chromosome paints from the Iberian Rock lizard I. monticola, and exemplifies their subsequent use in cross-species chromosome painting for carrying out comparative analyses of chromosome evolution in the congeneric species I. galani and I. bonnali, as well as in two other species of Lacertini, namely Lacerta schreiberi and Timon lepidus, whose sex chromosomes were also studied through comparative genomic hybridization. Most species of Lacertini possess a diplod number of 2n = 38, with 36 acrocentric macrochromosomes and 2 microchromosomes. However, the nine species included in the genus Iberolacerta do not possess microchromosomes, and additionally very conspicuous differences from the standard Lacertini karyotype are observed in the three Pyrenean species of this genus, including I. bonnali, with several biarmed metacentrics and a Z1Z2W multiple sex-chromosome system. All the species of the familiy Lacertidae, so far with the possible exception of L. schreiberi, appear to share homologous Z chromosomes, which date back to the last common ancestor of the whole group. We provide conclusive evidence that L. schreiberi should no longer be considered an exception to this rule, demonstrate that the loss of microchromosomes in Iberolacerta was produced by their fusion to a middle-sized chromosome, that the multiple sex-chromosome system of the Pyrenean species of Iberolacerta originated from the fusion of the ancestral W chromosome with one of the shortest autosomes, and provide additional evidence of the fast evolution of DNA sequences linked to the W chromosome in Lacertini.