Dispersal and adaptive radiation of Bidens (Compositae) across the remote archipelagoes of Polynesia

Authors: KNOPE, MATT - University Of Hawaii; FUNK, VICKI - Smithsonian Institute; Johnson, Melissa; WAGNER, WARREN - Smithsonian Institute; DATLOF, ERIN - University Of Hawaii; JOHNSON, GABRIEL - Smithsonian Institute; CRAWFORD, DANIEL - University Of Kansas; BONAFACINO, J - Universidad Del La Republica; MORDEN, CLIFFORD - University Of Hawaii; LORENCE, DAVID - National Tropical Botanical Garden (NTBG); WOOD, KENNETH - National Tropical Botanical Garden (NTBG); MEYER, JEAN-YVES - French Polynesia Government; CARLQUIST, SHERWIN - Santa Barbara Botanic Garden

Submitted to: Journal of Systematics and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/17/2020
Publication Date: 11/9/2020
Citation: Knope, M.L., Funk, V.A., Johnson, M.A., Wagner, W.L., Datlof, E.M., Johnson, G., Crawford, D., Bonafacino, J.M., Morden, C.W., Lorence, D.H., Wood, K.R., Meyer, J., Carlquist, S. 2020. Dispersal and adaptive radiation of Bidens (Compositae) across the remote archipelagoes of Polynesia. Journal of Systematics and Evolution. 58(6):805-822. https://doi.org/10.1111/jse.12704.
DOI: https://doi.org/10.1111/jse.12704

Interpretive Summary: Bidens is the largest genus of the tribe Compositae with estimates of 150-235 species, but the monophyly of the genus and number of species are in doubt. Attempts to develop a phylogenetic hypothesis for the tribe using morphological characters have resulted in limited resolution, and while recent genomic level sequencing provided the first fully bifurcating phylogenetic hypothesis for the Hawaiian taxa, many questions remain in terms of the evolutionary and biogeographical history of the group in the Pacific. The goals of this project were to: 1) test the monophyly of Bidens and of Coreopsis, the monophyly of the Polynesian Bidens radiation, and the monophyly of the individual archipelago-level radiations; 2) determine the location of the most recent common ancestor(s) of the Polynesian Bidens species;and 3) determine the timing and sequence of colonization events among the remote archipelagoes of the Pacific. These goals led us into a 15-year collecting effort of the Polynesian members of the tribe along with a broad sampling of related genera occurring in the Pacific Basin and elsewhere. This resulted in largely complete taxon sampling of the Polynesian Bidens radiation, and by far the greatest sampling of Bidens, Coreopsis, and related taxa undertaken to date.

Technical Abstract: The genus Bidens (Compositae) comprises c. 230 species distributed across five continents, with the 41 Polynesian species displaying the greatest eco-morphological variation in the group. However, the genus has had a long and complicated taxonomic history, and its phylogenetic and biogeographic history are poorly understood. In order to resolve the evolutionary history of the Polynesian Bidens, 152 individuals representing 91 species were included in this study, including 39 of the 41 described species from Polynesia. Four chloroplast and two nuclear DNA markers were utilized to estimate phylogenetic relationships, divergence times, and biogeographic history. Bidens was found to be polyphyletic within Coreopsis, consistent with prior assessments. The Polynesian radiation was resolved as monophyletic, with the initial dispersal into the Pacific possibly from South America to either the Hawaiian or Marquesas Islands. From the Marquesas, Bidens dispersed to the Society Islands, and ultimately to the Austral Islands. The initial diversification of the crown group in the Pacific is estimated to have occurred ~1.63 mya (0.74–2.72, 95% HPD), making Polynesian Bidens among the youngest and most rapid plant diversification events documented in the Pacific. Our findings suggest that relatively rare long-distance dispersal and founder event speciation, coupled with subsequent loss of dispersal potential and within-island speciation, can explain the repeated and explosive adaptive radiation of Bidens throughout the archipelagoes of Polynesia.