W Chromosome Evolution by Repeated Recycling in the Frog Glandirana rugosa

The Y or W sex chromosome of a heteromorphic pair is usually heterochromatinised and degenerated. However, whether degeneration constantly proceeds toward an extreme end not fully understood. Here, we present case intermittent evolution chromosomes caused by interpopulation hybridisation in the Japanese soil-frog, Glandirana rugosa. This species includes two systems, which are separated into geographic populations, namely XY ZW groups. In this study, to uncover evolutionary mechanisms heterogeneous chromosomes, genetically investigated differentiation populations along with closely located populations. Analysis mitochondrial cytochrome b sequences detected three distinct clades, named ZW1, ZW2, ZW3. High throughput analyses nuclear genomic DNA showed that autosomal alleles were deeply introgressed ZW3 sub-group. Based on genotypes sex-linked single nucleotide polymorphisms, W-borne androgen receptor gene expression, WW developmental mortality, concluded X recycled chromosomes. Upon inclusion cases from another group, Neo-ZW, observed independently at least four times new chromosomes: repetition resurrection.