The evolutionary history of the Caribbean magnolias (Magnoliaceae): Testing species delimitations and biogeographical hypotheses using molecular data

Abstract

The Caribbean islands provide an ideal setting for studying biodiversity, given their complex geological and environmental history, and their historical and current geographical proximity to the American mainland. Magnolia, a flagship tree genus that has 15 endemic and threatened taxa (12 species and 3 subspecies) on the Caribbean islands, offers an excellent case study to empirically test Caribbean biogeographical hypotheses. We constructed phylogenetic hypotheses to: (1) reveal their evolutionary history, (2) test the current largely morphology-based classification and assess species limits, and (3) investigate major biogeographic hypotheses proposed for the region. Nuclear and chloroplast DNA sequence data of all 15 Caribbean Magnolia taxa are included, supplemented by a selection of American mainland species, and species representing most major clades of the Magnoliaceae family. We constructed phylogenetic hypotheses in a time-calibrated Bayesian framework, supplemented with haplotype network analyses and ancestral range estimations. Genetic synapomorphies in the studied markers confirm the species limits of 14 out of 15 morphologically recognizable Caribbean Magnolia taxa. There is evidence for four colonization events of Magnolia into the Caribbean from the American mainland, which most likely occurred by overwater dispersal, given age estimates of maximum 16 mya for their presence on the Caribbean islands.