Kokia

Abstract: Long-distance insular dispersal is associated with divergence and speciation because of founder effects and strong genetic drift. The cotton tribe (Gossypieae) has experienced multiple transoceanic dispersals, generating an aggregate geographic range that encompasses much of the tropics and subtropics worldwide. Two genera in the Gossypieae, Kokia and Gossypioides, exhibit a remarkable geographic disjunction, being restricted to the Hawaiian Islands and Madagascar/East Africa, respectively. We assembled and use de novo genome sequences to address questions regarding the divergence of these two genera from each other and from their sister-group, Gossypium. In addition, we explore processes underlying the genome downsizing that characterizes Kokia and Gossypioides relative to other genera in the tribe. Using 13,000 gene orthologs and synonymous substitution rates, we show that the two disjuncts last shared a common ancestor ∼5 Ma, or half as long ago as their divergence from Gossypium. We report relative stasis in the transposable element fraction. In comparison to Gossypium, there is loss of ∼30% of the gene content in the two disjunct genera and a history of genome-wide accumulation of deletions. In both genera, there is a genome-wide bias toward deletions over insertions, and the number of gene losses exceeds the number of gains by ∼2- to 4-fold. The genomic analyses presented here elucidate genomic consequences of the demographic and biogeographic history of these closest relatives of Gossypium, and enhance their value as phylogenetic outgroups.

Abstract: Analyses were made of seeds and plant parts of 9 species of Cienfuegosia, 4 species of Thespesia, and 1 species of Kokia for content of gossypol and oil. The seeds of Cienfuegosia were nearly free of gossypol; the other plant parts contained much larger quantities. The desirability of a similar condition in cultivated cottons is discussed.

Abstract: Kokia (Malvaceae) is a tree genus consisting only of three endangered and one extinct species endemic to the Hawaiian Islands. Morphological and molecular population analyses suggested conflicting hypotheses as to colonization and dispersal among the Islands. To resolve this, 12 nuclear and four chloroplast gene regions were sequenced and compared to establish phylogenetic hypotheses and to make biogeographic inferences. Seven gene regions yielded phylogenies consistent with the progression rule hypothesis suggesting dispersal from older to younger islands, seven other gene regions were equivocal, and two weakly supported an alternative phylogeny. Combined analyses of all genes strongly supported the progression rule hypothesis, with initial colonization to Kaua‘i, or possibly an older and now submerged island, with subsequent dispersal to O‘ahu, Moloka‘i, and Hawai‘i Islands. Morphological characters plotted onto the molecular phylogeny suggested that many morphological traits are plastic or nonhomologous. Our study illustrates the perils of evaluating relationships among widely divergent taxa using morphological characters.

Abstract: Genetic diversity of all three extant species of the Hawaiian endemic tree genus Kokia was examined using analyses of RAPD markers. All three species are federally endangered, two (K. cookei and K. drynarioides) critically so, and one (K. kauaiensis) is rare but with several populations. Samples extracted were PCR amplified with 10 primers to yield 115 genetic markers. Analyses indicate that genetic variation is present in all three species; a surprising result given that K. cookei survives only from self-fertilized propagules of the single surviving individual that was grafted on to the root stock of a related species, K. drynarioides. Principal coordinates and cluster analyses based on RAPD markers indicate that although K. kauaiensis has substantial genetic variation, samples are clearly separate from the other two species of the genus. In contrast, K. cookei and K. drynarioides collections are more similar but still distinguishable when analyzed separately. Presence of substantial genetic variation lends optimism to the eventual recovery of K. kauaiensis through conservation efforts. Combinations of RAPD primers are suggested that reveal diagnostic alleles for each of the three extant species and can thus be used for species identification.