Memoirs of a frequent flier: Phylogenomics reveals 18 long-distance dispersals between North America and South America in the popcorn flowers (Amsinckiinae).

Am J Bot. 2017 Nov 23. doi: 10.3732/ajb.1700369. [Epub ahead of print] Guilliams CM1, Hasenstab-Lehman KE2, Mabry ME3, Simpson MG4. Author information 1 Department of Conservation and Research, Santa Barbara Botanic Garden, Santa Barbara, California 93105 USA mguilliams@sbbg.org msimpson@mail.sdsu.edu. 2 Department of Conservation and Research, Santa Barbara Botanic Garden, Santa Barbara, California 93105 USA. 3 Division of Biological Sciences and Bond Life Sciences Center, University of Missouri, Columbia, Missouri 65211 USA. 4 Department of Biology, San Diego State University, San Diego, California 92128 USA mguilliams@sbbg.org msimpson@mail.sdsu.edu. Abstract PREMISE OF THE STUDY: American amphitropical disjunction (AAD) is an important but understudied New World biogeographic pattern in which related plants occur in extratropical North America and South America, but are absent in the intervening tropics. Subtribe Amsinckiinae (Boraginaceae) is one of the richest groups of plants displaying the AAD pattern. Here, we infer a time-calibrated molecular phylogeny of the group to evaluate the number, timing, and directionality of AAD events, which yields generalizable insights into the mechanism of AAD. METHODS: We perform a phylogenomic analysis of 139 samples of subtribe Amsinckiinae and infer divergence times using two calibration schemes: with only fossil calibrations and with fossils plus a secondary calibration from a recent family level analysis. Biogeographic analysis was performed in the R package BioGeoBEARS. KEY RESULTS: We document 18 examples of AAD in the Amsinckiinae. Inferred divergence times of these AAD examples were strongly asynchronous, ranging from Miocene (17.1 million years ago [Ma]) to Pleistocene (0.33 Ma), with most (12) occurring <5 Ma. Four events occurred 10-5 Ma, during the second rise of the Andes. All AAD examples had a North America to South America directionality. CONCLUSIONS: Second only to the hyperdiverse Poaceae in number of documented AAD examples, the Amsinckiinae is an ideal system for the study of AAD. Asynchronous divergence times support the hypothesis of long-distance dispersal by birds as the mechanism of AAD in the subtribe and more generally. Further comparative phylogenomic studies may permit biogeographic hypothesis testing and examination of the relationship between AAD and fruit morphology, reproductive biology, and ploidy. © 2017 Botanical Society of America. KEYWORDS: Boraginaceae; Cryptantha; Great American Biotic Interchange; Oreocarya; Pacific Flyway; Pectocarya; Plagiobothrys; zoochory