Pagamea Aubl. (Rubiaceae), from species to processes, building the bridge

by Vicentini, Alberto

Species delimitation have a great impact in scientific, environmental and other human activities, and is fundamental for understanding evolution. Plant species are usually delimited based on morphology and rarely species concepts are stated and analysis of variation made explicit. Botanists do see species as “segments of evolutionary lineages”, but reproductive isolation is rarely addressed. Yet, reproductive isolation is necessary for understanding species, because speciation is the process of acquiring reproductive barriers. Almost any lineage will have species at different stages of isolation, and a single type of data will be insufficient for species delimitation. In plants, other biological processes such as hybridization, selfing and apomixis, make our search for species more challenging. If one focus on sympatry, reproductive isolation can be inferred, even if species are then defined only locally. If in a single locality putative species are distinct, then they must be reproductively isolated. Here, I first combine molecular phylogenetics (chloroplast and ITS), multivariate analyses of morphology, and sympatry for inferring reproductive isolation and delimiting species in Pagamea, a plant lineage from Tropical South America. I then used phylogenetic estimates of relationships to gain insights into the tempo and mode of speciation in this lineage. The results suggest 29 species in Pagamea. These include monophyletic and paraphyletic species, sympatric but cryptic species, and species that can be recognized only in a local sense. The ITS phylogeny best describes patterns of morphological, ecological and geographical variation, and the chloroplast shows a pattern consistent with the differential sorting of ancestral Vicentini, PhD. Dissertation, 2007, UMSL, p. iii polymorphisms. Pagamea started diversifying ~ 10 million year ago and all speciation events took place before the Pleistocene ( > 1.5 million years). Data exploration suggests peripatric speciation as the predominant mode in Pagamea, in agreement with the island-like distribution of its specific habitat (white-sand systems). Pagamea diversified along environmental gradients related to both flooding and altitude, with altitudinal shifts being phylogenetically more conserved than shifts for flooding levels. Eight new species of Pagamea are recognized and novel species circumscriptions are made. Hypothesis of species and intraspecific patterns of variation are also made explicit, and several interesting evolutionary scenarios emerge. Vicentini, PhD. Dissertation, 2007, UMSL, p. iv