Search for: All records

Abstract Island systems provide important contexts for studying processes underlying lineage migration, species diversification, and organismal extinction. The Hawaiian endemic mints (Lamiaceae family) are the second largest plant radiation on the isolated Hawaiian Islands. We generated a chromosome-scale reference genome for one Hawaiian species,Stenogyne calaminthoides, and resequenced 45 relatives, representing 34 species, to uncover the continental origins of this group and their subsequent diversification. We further resequenced 109 individuals of twoStenogynespecies, and their purported hybrids, found high on the Mauna Kea volcano on the island of Hawai’i. The three distinct Hawaiian genera,Haplostachys,Phyllostegia, andStenogyne, are nested inside a fourth genus,Stachys. We uncovered four independent polyploidy events withinStachys, including one allopolyploidy event underlying the Hawaiian mints and their direct western North American ancestors. While the Hawaiian taxa may have principally diversified by parapatry and drift in small and fragmented populations, localized admixture may have played an important role early in lineage diversification. Our genomic analyses provide a view into how organisms may have radiated on isolated island chains, settings that provided one of the principal natural laboratories for Darwin’s thinking about the evolutionary process. 

Societal Impact Statement Rafflesiais a genus of parasitic plants with the largest flowers in the world, unique to the threatened forest habitats of tropical Asia. Here, we report on genes that are active (the transcriptome) inRafflesiaseeds as part of a larger effort to understandRafflesia.Rafflesiahas never been grown successfully outside of its native range. Consequently, seed banking is not yet possible, precluding a critical management strategy for conservation. The study ofRafflesiaseed biology is a critical step to improve its cultivation, which will educate the public about unique species and the importance of conserving their habitats. SummaryRafflesiais of great interest as one of the only two plants known to have completely lost its chloroplast genome.Rafflesiais a holoparasite and an endophyte that lives inside the tissues of its host, a tropical grape vine (Tetrastigma), emerging only to bloom—with the largest flower of any plant. Here, we report the firstRafflesiaseed transcriptome and compare it with those of other plants to deepen our understanding of its extraordinary life history.We assembled a transcriptome from RNA extracted from seeds of the Philippine endemicRafflesia speciosaand compared this with those of other plants, includingArabidopsis, parasitic plantsStrigaandCuscuta, and the mycoheterotrophic orchidAnoectochilus.Genetic and metabolic seed pathways inRafflesiawere generally similar to the other plant species. However, there were some notable exceptions. We found evidence of horizontal transfer of a gene potentially involved in circumventing host defenses. Moreover, we identified a possible convergence among parasitic plants becauseRafflesia,Striga, andCuscutashared important similarities. We were unable to find evidence of genes involved in mycorrhizal symbiosis, suggesting that mycoheterotrophy is unlikely to play a role inRafflesiaparasitism.To date, ex situ propagation ofRafflesiaby seed has been mostly unsuccessful. Our research is a bold step forward in understanding the fundamentals ofRafflesiaseed biology that will inform the continued propagation and seed‐banking efforts concerning this recalcitrant plant. We discuss our findings in the broader context of the conservation of a genus in peril.