Cytogenetic Analysis of Seven Species of Gekkonid and Phyllodactylid Geckos

Abstract

Geckos (Gekkota), the species-rich clade of reptiles with more than 2200 currently recognized species, demonstrate a remarkable variability in diploid chromosome numbers (2n = 16–48) and mode of sex determination. However, only a small fraction of gekkotan species have been studied with cytogenetic methods. Here, we applied both conventional (karyotype reconstruction and C-banding) and molecular (fluorescence in situ hybridization with probes for rDNA loci and telomeric repeats) cytogenetic analyses in seven species of geckos, namely Blaesodactylus boivini, Chondrodactylus laevigatus, Gekko badenii, Gekko cf. lionotum, Hemidactylus sahgali, Homopholis wahlbergii (Gekkonidae) and Ptyodactylus togoensis (Phyllodactylidae), in order to provide further insights into the evolution of karyotypes in geckos. Our analysis revealed the presence of interstitial telomeric repeats in four species, but we were not able to conclude if they are remnants of previous chromosome rearrangements or were formed by an accumulation of telomeric-like satellite motifs. Even though sex chromosomes were previously identified in several species from the genera Hemidactylus and Gekko by cytogenetic and/or genomic methods, they were not detected by us in any examined species. Our examined species either have poorly differentiated sex chromosomes or, possibly, environmental sex determination. Future studies should explore the effect of temperature and conduct genome-wide analyses in order to identify the mode of sex determination in these species.

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

“…In particular, B. sakalava clade A and B and B. antongilensis showed a similar karyotype structure (with 2n = 40 and the occurrence of biarmed elements), with differences concerning the morphology of pairs 1 and 6. On the other hand, a different chromosome number (2n = 42) with only telocentric chromosomes was shown by B. boivini, as recently reported also by Chrostek et al [20].…”

“…In this study we performed the first comparative cytogenetic study on Blaesodactylus, providing the karyotype description of three different clades of this endemic Malagasy genus (B. sakalava clade A and B and B. antongilensis) and re-description of the karyotype of B. boivini (see also [20]). This contribution represents the first step in describing the karyological variability occurring in the genus Blaesodactylus, as well as a new contribution to reconstruct chromosomal evolutionary dynamics in a larger clade of the family Gekkonidae, which also includes the genera Homopholis and Geckolepis (Figure 1) (see also [19]).…”

“…The genus Blaesodactylus currently includes six described species (B. ambonihazo, B. antongilensis, B. boivini, B. victori, B. microtuberculatus and B. sakalava), which have been recently studied with morphological and molecular methods [16][17][18][19]. In contrast, chromosome analyses have been performed so far only on samples ascribed to B. boivini based on morphological characters [20], leaving the karyological variability of the genus completely unexplored. Concerning B. boivini, Chrostek et al [20] analyzed one male and one female sample of the species and described a karyotype composed of 2n = 42, with only telocentric chromosomes which gradually decrease in length.…”

“…In contrast, chromosome analyses have been performed so far only on samples ascribed to B. boivini based on morphological characters [20], leaving the karyological variability of the genus completely unexplored. Concerning B. boivini, Chrostek et al [20] analyzed one male and one female sample of the species and described a karyotype composed of 2n = 42, with only telocentric chromosomes which gradually decrease in length. Blocks of heterochromatin were identified on the centromeres of the six largest chromosome pairs and both sexes showed the same chromosome complement, without any evident heteromorphic sex chromosome pair.…”

“…Blocks of heterochromatin were identified on the centromeres of the six largest chromosome pairs and both sexes showed the same chromosome complement, without any evident heteromorphic sex chromosome pair. NORs were identified on the centromeric region of the first chromosome pair and telomeric repeats were localized at the centromeres of all chromosome pairs as well as at interstitial positions of several pairs [20].…”