Evolution of the Caribbean Species of Columnea (Gesneriaceae) with an Emphasis on the Jamaican Species

Abstract

Premise of research. Biogeography has improved understanding of evolution and diversification of organisms on both continental and island systems. One complicated island group in terms of geological history and biogeographic pattern is the Caribbean island system. A comparison across taxonomic groups does not result in overarching patterns for this group of islands. Columnea has the greatest number of species endemic to the Caribbean for any genus in Gesneriaceae that is not mostly endemic to the Caribbean with 16 species. Thirteen of these species are found on Jamaica, the remaining three each endemic to Cuba, Hispaniola, and Puerto Rico. In addition, populations of Columnea sanguinea and Columnea scandens are known from both mainland and multiple Caribbean islands. We investigate the pattern of evolution in Caribbean species of Columnea and attempt to explain the large number of species found on the island of Jamaica relative to the other islands. We explicitly test whether Caribbean species of Columnea are monophyletic and whether the 13 species endemic to Jamaica are a monophyletic group. This genus can help understand biogeographic patterns and modes of speciation in the Caribbean.Methodology. We sampled all Caribbean species of Columnea using DNA sequence data and phylogenetic methods to understand the pattern of diversity to determine whether multiple or single introductions could explain the diversity on the Caribbean islands.Pivotal results. The Caribbean species do not form a monophyletic group. The Jamaican species are monophyletic, and the endemic Cuban species, Columnea tincta, is sister to 12 of the Jamaican species, with Columnea pubescens sister to C. tincta + remaining Jamaican species. Most Jamaican species share similar corolla morphologies to section Columnea. Although never recovered as part of section Columnea, approximately unbiased tests cannot reject a sister group relationship of the Jamaican/Cuban endemic clade to section Columnea but can reject inclusion in section Columnea.Conclusions. The high diversity of Columnea in the Caribbean is due to the disproportionate number of species on Jamaica, but there is no obvious explanation for the radiation on this island, despite considering island size, topography, pollinators, and dispersers. The large number of species could be attributed to over-splitting on Jamaica, but even if a narrower concept were followed, and four of the species were combined as varieties of Columnea hirsuta as earlier taxonomy had predicted, the number of morphologically distinctive species would still be nine and much greater than that of the other islands. Our data also indicate that C. hirsuta sensu lato is not monophyletic.