The Caribbean Magnolia species (Magnoliaceae) : assessment of the genetic diversity and the underlying evolutionary history

Abstract

This PhD thesis discusses the importance of conserving the genus Magnolia, particularly in the Americas, where most of the diversity of the genus is found. Magnolia trees provide a range of services, including cultural services, regulating services, and potential provisioning services. Unfortunately, 48% of the 300 currently assessed Magnolia species are listed as threatened on the IUCN Red List, and 31% are Data Deficient. One area contributing to this high number of threatened Magnolias is the Caribbean. All 15 Caribbean Magnolia taxa are endemic to a specific Caribbean island, resulting in a small area of occupancy and extent of occurrence. The author conducted extensive fieldwork and used molecular data to study the genetic diversity of the 15 threatened Caribbean Magnolias. The data provided evidence for four colonization events of Magnolia into the Caribbean, estimated to have occurred maximum 16 million years ago. Overwater dispersal was found to be the most plausible dispersal hypothesis for their presence in the Caribbean islands. The inclusion of additional nuclear markers and the usage of coalescent theory species tree building methods did not deliver a more conclusive family-level phylogenetic hypothesis. The taxon delimitations of Caribbean Magnolias were mainly tested by means of phylogenetic hypotheses complemented with a haplotype network analysis. The results confirm the delimitation of 14 out of 15 Caribbean Magnolias, with the exception of the M. minor / M. oblongifolia species complex from Cuba, which urgently needs further investigation.