Independent domestication of two old world cotton species

Abstract

Domesticated cotton species provide raw material for the majority of the world's textile industry. Two independent domestication events have been identified in allopolyploid cotton, one in Upland cotton (Gossypiumhirsutum L.) and the other to Egyptian cotton (Gossypium barbadense L.). However, two diploid cotton species, Gossypium arboreum L. and Gossypiumherbaceum L., have been cultivated for several millennia, but their status as independent domesticates has long been in question. Using genome resequencing data,we estimated the global abundance of various repetitiveDNAs.We demonstrate that, despite negligible divergence in genome size, the two domesticated diploid cotton species contain different, but compensatory, repeat content and have thus experienced cryptic alterations in repeat abundance despite equivalence in genome size. Evidence of independent origin is bolstered by estimates of divergence times based onmolecular evolutionary analysis of f7,000 orthologous genes, forwhich synonymous substitution rates suggest that G. arboreumand G. herbaceum last shared a commonancestor approximately 0.4-2.5Ma. These data are incompatible with a shared domestication history during the emergence of agriculture and lead to the conclusion that G. arboreum and G. herbaceum were each domesticated independently.