Cytogenetic Analysis Did Not Reveal Differentiated Sex Chromosomes in Ten Species of Boas and Pythons (Reptilia: Serpentes)

Abstract

Homologous and differentiated ZZ/ZW sex chromosomes (or derived multiple neo-sex chromosomes) were often described in caenophidian snakes, but sex chromosomes were unknown until recently in non-caenophidian snakes. Previous studies revealed that two species of boas (Boa imperator, B. constrictor) and one species of python (Python bivittatus) independently evolved XX/XY sex chromosomes. In addition, heteromorphic ZZ/ZW sex chromosomes were recently revealed in the Madagascar boa (Acrantophis sp. cf. dumerili) and putatively also in the blind snake Myriopholis macrorhyncha. Since the evolution of sex chromosomes in non-caenophidian snakes seems to be more complex than previously thought, we examined ten species of pythons and boas representing the families Boidae, Calabariidae, Candoiidae, Charinidae, Pythonidae, and Sanziniidae by conventional and molecular cytogenetic methods, aiming to reveal their sex chromosomes. Our results show that all examined species do not possess sex-specific differences in their genomes detectable by the applied cytogenetic methods, indicating the presence of poorly differentiated sex chromosomes or even the absence of sex chromosomes. Interestingly, fluorescence in situ hybridization with telomeric repeats revealed extensive distribution of interstitial telomeric repeats in eight species, which are likely a consequence of intra-chromosomal rearrangements.

Cytogenetic Evidence for Sex Chromosomes and Karyotype Evolution in Anguimorphan Lizards

“…In addition, telomeric-like sequences are often part of the (peri)centromeric satellite motifs [ 65 , 66 ]. Overall, the presence of ITRs is quite rare in anguimorphan reptiles, in comparison to other toxicoferan reptiles, such as “haenophidian” snakes [ 67 ] and chameleons [ 49 ].…”

Interstitial Telomeric Repeats Are Rare in Turtles

“…Non-recombining parts of the unpaired W and Y chromosomes tend to degenerate, i.e., to lose functional genes [ 107 , 108 , 109 ], and to accumulate repeats such as microsatellites [ 49 , 53 , 56 , 62 , 110 , 111 ], rDNA-derived repeats [ 50 , 73 , 81 , 112 ] and telomeric-like repeats [ 27 , 28 , 61 , 113 , 114 , 115 ]. In turtles, the Y chromosome is not enriched in telomeric-like sequences in Glyptemys insculpta [ 76 ], Staurotypus salvinii and S. triporcatus [ 76 ].…”

“…Cytogenetic studies have detected ITRs in numerous species across vertebrate lineages, including mammals, fishes, birds, non-avian reptiles and amphibians [3,[27][28][29][30][39][40][41][42][43][44][45][46]. In non-avian reptiles, distribution of telomeric sequences have been extensively studied in squamates, i.e., lizards and snakes, where ITRs were detected in approximately 100 species, despite the generally conserved chromosome morphology in this group [28,45,[47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64]. It was proposed that intrachromosomal rearrangements might have a crucial role in the formation of ITRs in squamate reptiles [28,63].…”

Landscape of snake’ sex chromosomes evolution spanning 85 MYR reveals ancestry of sequences despite distinct evolutionary trajectories

“…Although suggested as having an independent origin, the homomorphic XX/XY chromosomes in Boa and Python are yet to be characterized by molecular cytogenetic techniques. Thus, their relationships and transitions among both homomorphic and heteromorphic ZZ/ZW in Pythonoidea and Booidea superfamilies 31 – 33 still remain unanswered. In the amazonian red-tailed Boa constrictor (formally Boa constrictor constrictor ), which has 2n = 36 chromosomes, the fourth chromosomal pair is thought to represent the putative sex pair, which would be a typical feature for henophidians (i.e.…”