Sex chromosome evolution in moths and butterflies

概要

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Lepidoptera, i.e. moths and butterflies, have a female heterogametic sex chromosome system, with most females having a WZ constitution while males are ZZ. Besides this predominant WZ/ZZ system, Z/ZZ, WZ1Z2/Z1Z1Z2Z2 and W1W2Z/ZZ systems also occur. Sex is determined by an unknown W-linked gene or genes in Bombyx mori, but by dosage-dependent and equally unknown Z-linked genes in all Z/ZZ species. The female-heterogametic sex chromosome system has been conserved for at least 180 milliion years in the phylogenetic branch that combines Lepidoptera and Trichoptera. The W chromosome, which is present in most lepidopteran species, was incorporated into the system much later, about 90-100 MYA. The Z chromosomes display conserved synteny, much like the Z in birds or the X in mammals. The W, on the other hand, is evolving rapidly. It is crammed with repetitive elements which appear to have a high turnover rate, but poor in or even devoid of protein-coding genes. It has frequently undergone fusion with autosomes or sporadically been lost altogether.