Phylogenomics and biogeography of Castanea (chestnut) and Hamamelis (witch-hazel): Choosing between RAD-seq and Hyb-Seq approaches

Target enrichment and RAD-seq are well-established high throughput sequencing technologies that have been increasingly used for phylogenomic studies. Each method has its own pros and cons. The choice between them is a practical issue for plant systematists studying the evolutionary histories of biodiversity of rela­tively recent origins. However, few studies have compared the congruence and conflict between results from the two methods within the same group of organisms in plants. In this study, we employed RAD-seq and Hyb-Seq of Angiosperm 353 genes in phylogenomic and biogeographic studies of Hamamelis (the witch-hazels) and Castanea (chestnuts), two classic examples exhibiting the well-known eastern Asian (EA)-eastern North American (ENA) disjunct distribution, and compared them side by side. Our results showed congruences in phylogenetic inference and divergence time dating between the two data sets obtained through our customized procedures of library preparation and sequence trimming, although they differed in the number of loci and informative sites, the amount of missing data, and sampling within species. We suggest the selection of the two methods based on fund availability and sampling scale. Our phylogenetic analyses of RAD-seq and Hyb-Seq data resulted in well-resolved species relationships, and ancient introgressions were revealed in both genera by D-statistic test and PhyloNet. Biogeographic analyses including fossil data using total evidence-based dated tree and DEC model, applying specific inter-area dispersal probabilities, revealed a complicated history for each genus, indicating multiple intercontinental dispersals and local extinctions in areas outside of the taxa's modern ranges in both the Paleogene and Neogene. The study demonstrates the importance of including fossil taxa for a more accurate reconstruction of biogeographic histories of taxa to understand the EA and ENA floristic disjunction. Our results support an "out of western North America" migration of Castanea but an "out of Asia" migration of Hamamelis during their initial diversification, and the origins of the EA-ENA disjunction in both genera were results of vicariance.