Genomic diversity and evolution in the Hawaiian Islands endemic Kokia (Malvaceae)

Abstract

AbstractIsland species are highly vulnerable due to habitat destruction and their often small population sizes with reduced genetic diversity. The Hawaiian Islands constitute the most isolated archipelago on the planet, harboring many endemic species.Kokiais an endangered flowering plant genus endemic to these islands, encompassing three extant and one extinct species. Recent studies provided evidence of unexpected genetic diversity withinKokia. Here, we provide high quality genome assemblies for all three extantKokiaspecies, including an improved genome forK. drynarioides. All threeKokiagenomes contain 12 chromosomes exhibiting high synteny within and betweenKokiaand the sister taxonGossypioides kirkii. Gene content analysis revealed a net loss of genes inK. cookeicompared to other species, whereas the gene complement inK. drynarioidesremains stable and that ofK. kauaiensisdisplays a net gain. A dated phylogeny estimates the divergence time from the last common ancestor for the threeKokiaspecies at ∼1.2 million years ago (mya), with the sister taxa [K. cookei + K. drynarioides] diverging ∼0.8 mya.Kokiaappears to have followed a stepping-stone pattern of colonization and diversification of the Hawaiian Archipelago, likely starting on low or now submerged older islands. The genetic resources provided may benefit conservation efforts of this endangered endemic genus.