Minute Y chromosomes and karyotype evolution in Madagascan iguanas (Squamata: Iguania: Opluridae)

Iguanas (Pleurodonta) are predominantly distributed in the New World, but one previously cytogenetically understudied family, Opluridae, is endemic to Madagascar and the adjacent Grand Comoro archipelago. The aim of our contribution is to fill a gap in the cytogenetic understanding of this biogeographically puzzling lineage. Based on examination of six species, we found that oplurids are rather conservative in karyotype, which is composed of 36 chromosomes as in most iguanas. However, the species differ in the position of the nucleolar organizer region and heterochromatic blocks and in the accumulation and distribution of interstitial telomeric sequences (ITSs), which suggests cryptic intra‐ and interchromosomal rearrangements. All tested species share the XY sex‐determining system homologous to most other iguana families. The oplurid Y chromosome is degenerated, very small in size but mostly euchromatic. Fluorescence in situ hybridization with probes composed of microsatellite motifs revealed variability among species in the accumulation of particular repeats on the Y chromosome. This variability accounts for the differences in the detection of sex chromosomes across the species of the family using comparative genome hybridization (CGH) technique. Our study demonstrates the limits of the commonly used CGH technique to uncover sex chromosomes even in organisms with heteromorphic and sequentially largely differentiated sex chromosomes.