Phylogenomics of the tetraploid Hawaiian lobeliads: Implications for their origin, dispersal history, and adaptive radiation

Hawaiian lobeliads exhibit extensive adaptive radiations and are
considered the largest plant clade (143 species) endemic to any oceanic
archipelago. Rapid insular radiations are prone to reticulate evolution,
yet detecting hybridization has been limited by species sampling or
inadequate nuclear data in previous Hawaiian studies. We analyzed 633
nuclear loci (including tetraploid duplications) and whole plastomes for
89% of extant species to derive phylogenies for the Hawai­ian lobeliads.
Nuclear data provide strong support for nine major clades in both
likelihood and ASTRAL analyses. All genera/sections are monophyletic
except Clermontia and Cyanea. Nuclear and plastome phylogenies conflict on
short, deep branches; the nuclear tree resolves a fleshy-fruited clade of
Hawaiian Clermontia/Cyanea-Brighamia/Delissea, sister to Polynesian
Sclerotheca, with both sister to a capsular-fruited Hawaiian clade.
Incomplete lineage sorting in a rapid radiation starting 8.5-11.3 million
years ago is sufficient to explain uncertainty and cytonuclear discordance
along the backbone; sequence data strongly supports reticulation within
Clermontia and especially Cyanea. Nuclear data identify 42 inter-island
dispersal events, of which 89% accord with the progression rule, involving
movement to the next younger, formerly unoccupied islands in the hotspot
chain, consistent with ecological theory; plastid data overestimate such
dispersals by 17%. Clermontia and Cyanea have undergone parallel adaptive
radiations in elevational distribution and flower length on all major
islands, but with some inter-island divergence. Within-island adaptive
radiation and ecological speciation in these traits within
Clemontia/Cyanea, combined with widespread single-island endemism,
frequent inter-island dispersal, and occasional hybridization drove
Hawaiian lobeliad diversification, together with early intergeneric
divergence in habitat.