Phylogenomics of the Caribbean melocacti: Cryptic species and multiple invasions

Abstract

AbstractThe widespread Neotropical genus Melocactus of approximately 42 currently recognized species, is most diverse in eastern Brazil and the Greater Antilles, especially Cuba. Species delimitation is notoriously problematic in the group, although this is due in part to a lack of detailed systematic studies, as well as a severely cluttered nomenclatural history. To date, no comprehensive phylogenetic hypotheses have been generated for the clade, although some population genetic and morphological studies exist. We generated the largest phylogenetic dataset of Melocactus to date based on plastome data derived from a genome‐skimming approach for 26 taxa, which provided a framework for understanding species limits and relationships among Caribbean species. Our time‐calibrated phylogeny revealed a mid‐Pleistocene origin for Melocactus, and we resolved three major clades, a Cuban clade, a mostly South American clade, and a widespread Caribbean clade, which also included some South American taxa. Our topology recovered the Cuban clade as sister to the rest of the species, although this placement was poorly supported, and several other Cuban species are scattered throughout the rest of the tree. Biogeographic analyses suggested multiple dispersal events from South America leading to the current diversity on Cuba, as well as other parts of the Antilles. Based on our phylogenetic results, previous hypotheses of species numbers and relationships in the Caribbean generated solely on morphology have, in some cases, been greatly underestimated. Our study shows that plastome data are effective for resolving clades and species limits in Melocactus, although future work will need to include broader sampling and larger datasets to fully resolve relationships in this complicated group of cacti. We describe one new cryptic species for Cuba, Melocactus santiagoensis sp. nov., and provide a new combination (Melocactus lagunaensis comb. & stat. nov.), based on our phylogenetic results and morphological data and typify numerous names in the genus. The genus Melocactus is another striking example of the exceptional diversity that has been generated in the poorly studied, seasonally dry tropical forest of the Greater Antilles.