Stable Cretaceous sex chromosomes enable molecular sexing in softshell turtles (Testudines: Trionychidae)

AbstractOrganisms evolved various mechanisms to cope with the differences in the gene copy numbers between sexes caused by degeneration of Y and W sex chromosomes. Complete dosage compensation or at least expression balance between sexes was reported predominantly in XX/XY, but rarely in ZZ/ZW systems. However, this often-reported pattern is based on comparisons of lineages where sex chromosomes evolved from non-homologous genomic regions, potentially differing in sensitivity to differences in gene copy numbers. Here we document that two reptilian lineages (XX/XY iguanas and ZZ/ZW softshell turtles), which independently co-opted the same ancestral genomic region for the function of sex chromosomes, evolved different gene dose regulatory mechanisms. The independent co-option of the same genomic region for the role of sex chromosome as in the iguanas and the softshell turtles offers a great opportunity for testing evolutionary scenarios on the sex chromosome evolution under the explicit control for the genomic background and for gene identity. We showed that the parallel loss of functional genes from the Y chromosome of the green anole and the W chromosome of the Florida softshell turtle led to different dosage compensation mechanisms. Our approach controlling for genetic background thus does not support that the variability in the regulation of the gene dose differences is a consequence of ancestral autosomal gene content.

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Poorly differentiated XX/XY sex chromosomes are widely shared across skink radiation

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2020.2139 ◽

2021 ◽

Vol 288 (1943) ◽

pp. 20202139

Author(s):

Alexander Kostmann ◽

Lukáš Kratochvíl ◽

Michail Rovatsos

Keyword(s):

Species Diversity ◽

Sex Determination ◽

Sex Chromosomes ◽

Morphological Variability ◽

Molecular Sexing ◽

Diverse Group ◽

Reptile Species ◽

Poorly Differentiated ◽

The Common ◽

Evolutionarily Stable

Differentiated sex chromosomes are believed to be evolutionarily stable, while poorly differentiated sex chromosomes are considered to be prone to turnovers. With around 1700 currently known species forming ca 15% of reptile species diversity, skinks (family Scincidae) are a very diverse group of squamates known for their large ecological and morphological variability. Skinks generally have poorly differentiated and cytogenetically indistinguishable sex chromosomes, and their sex determination was suggested to be highly variable. Here, we determined X-linked genes in the common sandfish ( Scincus scincus ) and demonstrate that skinks have shared the same homologous XX/XY sex chromosomes across their wide phylogenetic spectrum for at least 85 million years, approaching the age of the highly differentiated ZZ/ZW sex chromosomes of birds and advanced snakes. Skinks thus demonstrate that even poorly differentiated sex chromosomes can be evolutionarily stable. The conservation of sex chromosomes across skinks allows us to introduce the first molecular sexing method widely applicable in this group.

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Sex determination of Neotropic cormorant (Phalacrocorax brasilianus) by molecular sexing

Avian Biology Research ◽

10.1177/1758155919832130 ◽

2019 ◽

Vol 12 (1) ◽

pp. 10-12

Author(s):

Pedro Rodrigues ◽

Elena Campos ◽

Joana Micael ◽

Claudio Verdugo

Keyword(s):

Sex Chromosomes ◽

Z Chromosome ◽

Molecular Technique ◽

Molecular Sexing ◽

W Chromosome ◽

American Continent ◽

Base Pairs ◽

Male And Female ◽

Phalacrocorax Brasilianus

Neotropic cormorant ( Phalacrocorax brasilianus) is a monomorphic species widely distributed along the American Continent. We used a rapid and efficient molecular technique centred on the chromo-helicase-DNA-binding gene in order to differentiate male and female sex chromosomes based on the size of introns. Males presented a Z chromosome with a single band of 664 base pairs, and females presented the same band plus a shortest one corresponding to the W chromosome with 459 base pairs.

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Evolutionary stability of sex chromosomes in snakes

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2015.1992 ◽

2015 ◽

Vol 282 (1821) ◽

pp. 20151992 ◽

Cited By ~ 46

Author(s):

Michail Rovatsos ◽

Jasna Vukić ◽

Petros Lymberakis ◽

Lukáš Kratochvíl

Keyword(s):

Sex Determination ◽

Quantitative Pcr ◽

Sex Chromosomes ◽

Evolutionary Stability ◽

Molecular Evidence ◽

Molecular Sexing ◽

Snake Species ◽

Long Term Stability ◽

Monitor Lizards

Amniote vertebrates possess various mechanisms of sex determination, but their variability is not equally distributed. The large evolutionary stability of sex chromosomes in viviparous mammals and birds was believed to be connected with their endothermy. However, some ectotherm lineages seem to be comparably conserved in sex determination, but previously there was a lack of molecular evidence to confirm this. Here, we document a stability of sex chromosomes in advanced snakes based on the testing of Z-specificity of genes using quantitative PCR (qPCR) across 37 snake species (our qPCR technique is suitable for molecular sexing in potentially all advanced snakes). We discovered that at least part of sex chromosomes is homologous across all families of caenophidian snakes (Acrochordidae, Xenodermatidae, Pareatidae, Viperidae, Homalopsidae, Colubridae, Elapidae and Lamprophiidae). The emergence of differentiated sex chromosomes can be dated back to about 60 Ma and preceded the extensive diversification of advanced snakes, the group with more than 3000 species. The Z-specific genes of caenophidian snakes are (pseudo)autosomal in the members of the snake families Pythonidae, Xenopeltidae, Boidae, Erycidae and Sanziniidae, as well as in outgroups with differentiated sex chromosomes such as monitor lizards, iguanas and chameleons. Along with iguanas, advanced snakes are therefore another example of ectothermic amniotes with a long-term stability of sex chromosomes comparable with endotherms.

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Poorly differentiated XX/XY sex chromosomes are widely shared across skink radiation

10.1101/2020.08.29.273524 ◽

2020 ◽

Cited By ~ 2

Author(s):

Alexander Kostmann ◽

Lukáš Kratochvíl ◽

Michail Rovatsos

Keyword(s):

Species Diversity ◽

Sex Chromosomes ◽

Morphological Variability ◽

The Other ◽

Molecular Sexing ◽

Diverse Group ◽

Reptile Species ◽

Poorly Differentiated ◽

The Common ◽

Evolutionarily Stable

AbstractDifferentiated sex chromosomes are believed to be evolutionarily stable, and their emergence was suggested to lead to a remarkable increase in the diversification rate and in disparity in such groups as birds, mammals and snakes. On the other hand, poorly differentiated sex chromosomes are considered to be prone to turnovers. With around 1.700 currently known species forming c. 15% of reptile species diversity, skinks (family Scincidae) are a very diverse group of squamates known for their large ecological and morphological variability. Skinks generally have poorly differentiated and cytogenetically hardly distinguishable sex chromosomes and their sex determination was suggested to be highly variable. Here, we determined X-linked genes in the common sandfish (Scincus scincus) and demonstrate that skinks have shared the same homologous XX/XY sex chromosomes across their wide phylogenetic spectrum for at least 85 million years, approaching the age of the highly differentiated ZZ/ZW sex chromosomes of birds and advanced snakes. Skinks thus demonstrate that even poorly differentiated sex chromosomes can be evolutionarily stable and that large diversity can emerge even in groups with poorly differentiated sex chromosomes. The conservation of sex chromosomes across skinks allows us to introduce the first molecular sexing method widely applicable in this group.

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