Assessing phylogeny and biogeography in a megadiverse tropical plant family (Melastomataceae)
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Abstract
Melastomataceae are among the ten most species-rich families of angiosperms. They are primarily distributed in tropical and subtropical regions globally where they form subdominant components of the vegetation in many biodiversity hotspots. Many species are light gap colonizers playing significant roles in the successional recovery of forests following disturbance. Most of the ca. 5000 species provide pollen rewards for buzz-pollinating bees, though shifts to nectar rewards for vertebrate floral visitors have occurred numerous times. The berry fruits of about 3000 species are a food source for birds, mammals, and fishes. Mites and ants living in domatia often form mutualistic associations with their melastome host plants.
Over 55 genera and 2000 species have been described since the Melastomataceae were last monographed in 1891. Classifications to date have proposed conflicting relationships at the tribal and generic levels and are based mostly on homoplasious morphological characters. Molecular phylogenetic analyses consistently show well-supported clades that are inconsistent with many tribal and generic circumscriptions; thus, past concepts of infrafamilial relationships must be considered provisional at best. Published phylogenetic analyses targeting the entire family have included less than 35% of the genera and about 15% of the species, rendering any attempt to propose a new classification premature. The large size of the Melastomataceae, its extraordinary diversity, and its pantropical distribution present some special opportunities to test hypotheses pertaining to biogeography, character evolution, and systematics.
The PIs propose to 1) test hypotheses of relationships in the Melastomataceae by conducting phylogenetic analyses of 1000 species and all 170 genera for nucleotide data from two nuclear and five chloroplast genic regions. This dense level of sampling will be achieved through targeted field work in tropical Asia, interaction with other ongoing projects in the family, and herbarium sampling, 2) use the tree based on the seven-marker data set to test hypotheses on the historical biogeography of the family, 3) survey seed characters with scanning electron microscopy (SEM), then use the tree to test their reported taxonomic utility at deep levels of the phylogeny, and 4) create an interactive key to the tribes and clearly monophyletic genera identified in the molecular analyses. The project will result in a combined phylogenetic analysis more than ten times larger than any comparable study published on the Melastomataceae. Results from this project will 1) overhaul the classification of the Melastomataceae, 2) improve the taxonomic framework for monographic and other studies, 3) set the stage for assessing the evolution of characters traditionally used to circumscribe the tribes and genera of the family, 4) test hypotheses regarding the evolution of various pollination syndromes and other mutualistic associations with ants and mites in tropical biomes, 5) test hypotheses on the historical biogeography of pantropical disjuncts, thus increasing understanding of plant responses to patterns of climate change, and 6) provide a new source of data to inform and direct conservation priorities in biodiversity-rich tropical countries.
