Turnover of sex defining mutation provides an insight into evolution of
sex chromosomes in the golden pompano (Trachinotus ovatus)
Abstract
The golden pompano (Trachinotus ovatus) is a marine fish species in the
family Carangidae. We constructed a chromosome-level genome assembly of
a male golden pompano. QTL-mapping and GWAS analysis showed that this
species has a ZZ/ZW sex determination system and a sex defining SNP
(Chr16:18219150:G/A), located on the splice donor site (GT-AG) of the
first intron of Hsd17b1, was exclusively associated with the phenotypic
sex. The W-linked coding sequences of Hsd17b1 were conserved across
vertebrates, while Z-linked coding sequences introduced extra 64 bases
and were malfunctional. The golden pompano and the greater amberjack
(Seriola dumerili), divergent in 57 million years ago in the same
family, share the same features of sex determination, including the same
sex determining gene, malfunctional Z-linked haplotypes,
undifferentiated sex chromosomes except that the sex defining SNPs are
different. In simulation analysis, turnover of sex determining mutation,
single mutation dominating sex determination and undifferentiated sex
chromosomes were also observed. We proposed a hypothesis that W-linked
haplotypes of the sex determining gene of Hsd17b1 were under purifying
selection, Z-linked haplotypes may evolve near neutrally, recurrent and
directional transformations from W-linked haplotypes to Z-linked
haplotypes caused by inactivating mutations, relatively strong forces of
drift and recombination comprehensively contributed to turnover of sex
defining mutation and undifferentiation of sex chromosome. We also
established zebrafish mutants and homozygous mutants were “all male”,
which indirectly supported this hypothesis.