Phylogeny and biogeography of Ceiba Mill. (Malvaceae, Bombacoideae)

Abstract

The Neotropics is the most species-rich area in the world and the mechanisms that generated and maintain its biodiversity are still debated. This paper contributes to the debate by investigating the evolutionary and biogeographic history of the genus Ceiba Mill. (Malvaceae: Bombacoideae). Ceiba comprises 18 mostly neotropical species endemic to two major biomes, seasonally dry tropical forests (SDTFs) and rain forests and its species are one of the most characteristic elements of neotropical SDTF, one of the most threatened biomes in the tropics. Phylogenetic analyses of DNA sequence data from the nuclear ribosomal internal transcribed spacers (ITS) for 30 accessions representing 14 species of Ceiba recovered the genus as monophyletic and showed geographical and ecological structure in three main clades: (i) a rain forest lineage of nine accessions of C. pentandra sister to the remaining species; (ii) a highly supported clade composed of C. schottii and C. aesculifolia from Central American and Mexican SDTF plus two accessions of C. samauma from inter Andean valleys from Peru; and (iii) a highly supported South American SDTF clade including 10 species showing little sequence variation. Within this South American clade, no species represented by multiple accessions were resolved as monophyletic. We demonstrate that the patterns of species age, monophyly and geographical structure previously reported for SDTF species within the Leguminosae family are not shared by Ceiba, suggesting that further phylogenetic studies of unrelated groups are required. HIGHLIGHTSO_LIThis paper provides a well sampled phylogeny of the iconic genus Ceiba, one of the most characteristic tree genera of neotropical Seasonally Dry Tropical Forest (SDTF). C_LIO_LIThere is a clear phylogenetic signal for biome preference and geographic structure in Ceiba. C_LIO_LIWe estimate a mid Miocene origin for Ceiba, with the stem node age of the genus estimated at 21.1 Ma and the crown node age at 12.7 Ma. C_LIO_LICeiba species have young stem ages in the SDTF clade but old stem ages in rain forest species. C_LIO_LIPatterns of species age, monophyly, ecological and geographical structure reported for SDTF species are only partially shared by Ceiba, an iconic genus of neotropical SDTF. C_LI