Chromosome Diversity and Evolution of the Endemic Malagasy Velvet Geckos of the Genus Blaesodactylus (Reptilia, Gekkonidae)

SIMPLE SUMMARY: We implemented a molecular and phylogenetic analysis and a comparative karyological investigation with standard and chromosome banding methods on different taxa of the endemic Malagasy velvet geckos of the genus Blaesodactylus. We present the description of the karyotype of three different taxa and a characterization of the chromosomal diversity in the genus. We show the occurrence of karyological variability in the genus Blaesodactylus in terms of chromosome number (2n = 40–42), morphology, chromosome position of loci of NORs, and distribution pattern of heterochromatin. Considering our results together with the available information on evolutionary related gecko species, we hypothesize that the karyotype evolution in Blaesodactylus mostly involved a decrease in the total number of chromosomes and the formation of biarmed elements. We also highlight that similar pathways of chromosomal rearrangements have been previously observed in other geckos, possibly representing a convergent karyotype evolution. ABSTRACT: We performed a molecular and phylogenetic analysis and a comparative cytogenetic study with standard karyotyping, silver staining (Ag-NOR) and sequential C-banding + Giemsa, + fluorochromes on several Blaesodactylus samples. The phylogenetic inference retrieved two main clades, the first comprises B. victori, B. microtuberculatus and B. boivini, while the second includes B. sakalava, B. antongilensis and B. ambonihazo. The available samples of B. sakalava form two different clades (here named B. sakalava clade A and clade B), which probably deserve a taxonomic re-evaluation. We found a karyological variability in Blaesodactylus in terms of chromosome number (2n = 40–42), morphology, location of NORs, and heterochromatin distribution pattern. Blaesodactylus antongilensis and B. sakalava clade A and B showed a karyotype of 2n = 40 mostly telocentric chromosomes. Pairs 1 and 6 were metacentric in B. sakalava clade A and B, while pair 1 was composed of subtelocentric/submetacentric elements in B. antongilensis. In contrast, B. boivini displayed a karyotype with 2n = 42 only telocentric chromosomes. NORs were on the first chromosome pair in B. boivini, and on the second pair in B. antongilensis. Adding our data to those available from the literature on evolutionarily related species, we highlight that the chromosome diversification in the genus probably proceeded towards a progressive reduction in the chromosome number and the formation of metacentric elements.