Woody perennial plants on islands have repeatedly evolved from herbaceousmainland ancestors. Although the majority of species in Euphorbia subgenusChamaesyce section Anisophyllum (Euphorbiaceae) are small and herbaceous, aclade of 16 woody species diversified on the Hawaiian Islands. They are found in abroad range of habitats, including the only known C4 plants adapted to wet forestunderstories. We investigate the history of island colonization and habitat shift inthis group. We sampled 153 individuals in 15 of the 16 native species of HawaiianEuphorbia on six major Hawaiian Islands, plus 11 New World close relatives, toelucidate the biogeographic movement of this lineage within the Hawaiian islandchain. We used a concatenated chloroplast DNA data set of more than eight kilobases in aligned length and applied maximum likelihood and Bayesian inference forphylogenetic reconstruction. Age and phylogeographic patterns were co-estimatedusing BEAST. In addition, we used nuclear ribosomal ITS and the low-copy genesLEAFY and G3pdhC to investigate the reticulate relationships within this radiation.Hawaiian Euphorbia first arrived on Kauài or Nìihau ca. 5 million years ago andsubsequently diverged into 16 named species with extensive reticulation. Duringthis process Hawaiian Euphorbia dispersed from older to younger islands throughopen vegetation that is disturbance-prone. Species that occur under closed vegetation evolved in situ from open vegetation of the same island and are only foundon the two oldest islands of Kauài and Òahu. The biogeographic history ofHawaiian Euphorbia supports a progression rule with within-island shifts from opento closed vegetation.
Bibliographical noteFunding Information:
National Tropical Botanical Garden; Divisionof Environmental Biology, National ScienceFoundation, Award Number: 0616533.
We thank the following people for help with field work: Christian Torres-Santana, Kenneth Wood, Larry Abbott, Ane Bakutis, Lala Bialic-Murphy, Pat Bily, Joanne Birch, Matt Burt, Molly Cavaleri, Marian Chau, Susan Ching, Margaret Clark, Vince Costello, Michelle Elmore, Steve Evens, Erin Foley, Julia Gustine, Kapua Kawelo, Matt Keir, Tobias Koehler, Joel Lau, Matthew Lurie, Kristen Nalani Mailheau, Steve Perlman, Allen Rietow, Dan Sailor, Wayne Souza, Natalia Tangalin and Mashuri Waite. The field work was facilitated by the following agencies: Hawaii Department of Land and Natural Resources, Division of Forestry and Wildlife, O`ahu Army Natural Resources Program, the Center for Environmental Management of Military Lands, Colorado State University, Pohakuloa Training Area, Nature Conservancy of Hawaii, National Tropical Botanical Garden, and The Plant Extinction Prevention Program. We thank Hank Oppenheimer for providing plant materials; Lauren Raz and Timothy Motley for allowing us to used their unpublished DNA samples; Evan Economo and Jess Peirson for insightful discussions and comments on the manuscript. Funding was provided by the National Science Foundation through a Planetary Biodiversity Inventory award (DEB-0616533) to PEB and the National Tropical Botanical Garden through a McBryde Fellowship to PEB and YY.
© 2018 The Authors.
- Euphorbia subgenus Chamaesyce
- Hawaiian Islands
- Section Anisophyllum