131 | First evidence of karyotype diversity and evolution in endemic Scincinae (squamata: scincinae) from madagascar

Barbara Cirimele¹, Elvira Brunelli¹, Gaetano Odierna², Fabio M. Guarino², Valentina Basile¹, Marcello Mezzasalma¹ | ¹Department of Biology, Ecology and Earth Science, University of Calabria Rende, Cosenza, Italy; ²Department of Biology, University of Naples Federico II, Naples, Italy.

Karyotype evolution represents an important evolutionary driver. Chromosomal changes (or macromutations) can actively trigger processes of speciation and lineage divergence through the establishment of postzygotic reproductive barriers, or they can arise as a consequence of phylogenetic diversification. Madagascar is one of the world’s major biodiversity hotspots and hosts an astonishing reptile diversity, with more than 450 described endemic species. Among them, the lizards of the subfamily Scincinae represent one of the most species-rich squamate groups on the island, however, their karyotype diversity remains completely unexplored. In this study, we performed a preliminary molecular taxonomic identification and a comparative cytogenetic analysis of several biological samples of Malagasy Scincinae. Molecular analyses were conducted using a fragment of approximately 570 bp of the mitochondrial 16S rRNA gene to ascertain the taxonomic identity of the available samples. Subsequently, we carried out comparative chromosome analyses using standard karyotyping (5% Giemsa solution at pH 7) to provide the first karyotype descriptions of the studied taxa. Sequential C-banding followed by Giemsa, DAPI, and CMA₃ coloration was also performed to characterize chromosomal patterns of heterochromatin distribution. Molecular results identified the studied samples as belonging to two genera and three species of Malagasy Scincinae: Madascincus igneocaudatus, Madascincus melanopleura, and Pygomeles trivittatus. Cytogenetic analyses revealed that these three species share a generally similar karyotype organization, consisting of 2n = 24–26 mostly metacentric chromosomes, with species-specific differences related to chromosome number and the relative size of some chromosome pairs. In particular, the congeneric species M. igneocaudatus and M. melanopleura share the same chromosome complement (2n = 24), but differ in the size of chromosome pairs 5 and 6, which are larger in M. melanopleura. In contrast, P. trivittatus exhibits a karyotype composed of 2n = 26 chromosomes, with the first five metacentric pairs distinctly larger than the remaining eight pairs. C-banding revealed heterochromatin restricted to centromeric and telomeric regions, and no largely heterochromatic chromosomes were observed in any of the studied taxa. These results represent the first karyotype descriptions of endemic Malagasy Scincinae species and provide evidence of inter- and intrageneric karyotype diversity of taxonomic relevance. The observed differences likely result from a combination of chromosomal rearrangements, including inversions and chromosome fusions or fissions, highlighting the evolutionary relevance of cytogenetic data in this group.