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

Abstract

Most of snakes exhibit a ZZ/ZW sex chromosome system, with different stages of degeneration. However, undifferentiated sex chromosomes and unique Y sex-linked markers, suggest that an XY system has also evolved in ancestral lineages. Comparative cytogenetic mappings revealed that several genes share ancestry among X, Y and Z chromosomes, implying that XY and ZW may have undergone transitions during serpent’s evolution. In this study, we performed a comparative cytogenetic analysis to identify homologies of sex chromosomes across ancestral (Henophidia) and more recent (Caenophidia) snakes. Our analysis suggests that, despite ~ 85 myr of independent evolution, henophidians and caenophidians retained conserved synteny over much of their genomes. However, our findings allowed us to discover that ancestral and recent lineages of snakes do not share the same sex chromosome and followed distinct pathways for sex chromosomes evolution.

Cytogenetic Analysis of <b><i>Panaqolus tankei</i></b> Cramer &amp; Sousa, 2016 (Siluriformes, Loricariidae), an Ornamental Fish Endemic to Xingu River, Brazil

“…CGH experiments were performed exactly as detailed in our previous works [Cioffi et al, 2019;Viana et al, 2019Viana et al, , 2020. Briefly, the slides were incubated for 72 h at 37°C in a dark humid chamber.…”

Multiple Sex Chromosomes and Evolutionary Relationships in Amazonian Catfishes: The Outstanding Model of the Genus Harttia (Siluriformes: Loricariidae)

“…When sex chromosomes stop recombination, repetitive sequences are predicted to have a rapid accumulation on them [61], and microsatellite repeats seem to play a key role as "early colonizers" in their differentiation [24,62]. Numerous examples in animals and plants document a massive and differential accumulation of such small motifs in sex-specific chromosomes, particularly in simple (XY or ZW) systems [24,56,[63][64][65][66][67]. However, most X 1 X 2 Y systems lack substantial differentiation in the neo-Y, since the accumulation of repetitive DNAs (=large blocks of heterochromatin) would impair the proper pairing of the neo-sex chromosomes into a stable trivalent form, thus disturbing the meiotic process [68].…”

Revisiting the Karyotype Evolution of Neotropical Boid Snakes: A Puzzle Mediated by Chromosomal Fissions

“…Meanwhile, the ancestral state 2n = 36 is retained along the diversification and split among Eunectes, Epicrates, and Chilabothrus genera in the Paleogene/Neogene (Figure 4). Interestingly, the undifferentiated putative XY sex chromosomes of Boa constrictor [29,46] remained conserved in species with 2n = 36 (putative pair 4 in Eunectes and Epicrates) and with 2n = 40 (pair 5 in Corallus hortulana). On the other hand, in Corallus caninus (2n = 44), the putative XY chromosomes of Boa constrictor underwent fission events, giving rise to the smallest acrocentric chromosomes of the complement, pairs 11 and 12 (Figures 3 and 5).…”

“…Comparative mappings from the putative Boa XY derived probes in sister lineages, such as the well-differentiated ZW (also the 4th pair) present in Acrantophis [50], will certainly highlight the homologies of sequences as well as turnovers between the sex chromosome systems in these ancient groups of snakes. Interestingly, the undifferentiated putative XY sex chromosomes of Boa constrictor [29,46] remained conserved in species with 2n = 36 (putative pair 4 in Eunectes and Epicrates) and with 2n = 40 (pair 5 in Corallus hortulana). On the other hand, in Corallus caninus (2n = 44), the putative XY chromosomes of Boa constrictor underwent fission events, giving rise to the smallest acrocentric chromosomes of the complement, pairs 11 and 12 (Figures 3 and 5).…”