New Insights on Chromosome Diversification in Malagasy Chameleons

In this work, we performed a preliminary molecular analysis and a comparative cytogenetic study on 5 different species of Malagasy chameleons of the genus <i>Brookesia</i> (<i>B. superciliaris</i>) and <i>Furcifer</i> (<i>F. balteautus</i>, <i>F. petteri</i>, <i>F. major</i> and <i>F. minor</i>). A DNA barcoding analysis was first carried out on the study samples using a fragment of the mitochondrial gene coding for the cytochrome oxidase subunit 1 (COI) in order to assess the taxonomic identity of the available biological material. Subsequently, we performed on the studied individuals a chromosome analysis with standard karyotyping (5% Giemsa solution at pH 7) and sequential C-banding + Giemsa, + CMA₃, and + DAPI. The results obtained indicate that the studied species are characterized by a different chromosome number and a variable heterochromatin content and distribution, with or without differentiated sex chromosomes. In particular, <i>B. superciliaris</i> (2n = 36) and <i>F. balteatus</i> (2n = 34) showed a similar karyotype with 6 macro- and 12-11 microchromosome pairs, without differentiated sex chromosomes. In turn, <i>F. petteri</i>, <i>F. major</i>, and <i>F. minor</i> showed a karyotype with a reduced chromosome number (2n = 22-24) and a differentiated sex chromosome system with female heterogamety (ZZ/ZW). Adding our newly generated data to those available from the literature, we highlight that the remarkable chromosomal diversification of the genus <i>Furcifer</i> was likely driven by non-homologous chromosome fusions, including autosome-autosome, Z-autosome, and W-autosome fusions. The results of this process resulted in a progressive reduction in the chromosome number and partially homologous sex chromosomes of different shapes and sizes.