I am a Ph.D. candidate under the supervision of Dr. Paul V. A. Fine in the Department of Integrative Biology at the University of California Berkeley.

Visit the Fine Lab website to know more about Paul V. A. Fine

dissertation

Neotropical forests harbor the highest tree diversity on earth. Although plot-network research has enhanced our understanding on the floristics and the community ecology of tropical forests, very few have committed to face the systematic challenges and improve the taxonomic treatment of plant lineages, especially those morphologically incongruent. This is the case for Protium heptaphyllum (Aubl.) Marchand, a species complex included in a recent list of the most dominant and widespread trees across the Amazon basin. My research aims to disentangle the evolutionary history of this dominant tree and understand the role of habitat heterogeneity in promoting speciation of Neotropical plant lineages. I am integrating taxonomy, molecular phylogenetics (including genomics data from next-generation sequencing) and phylogeography with a functional approach to understand the role that adaptive selection versus phenotypic plasticity is playing in allowing this tree to live in so many different environments.The results will shed light on the systematics of hyperdominant taxa being relevant to plant taxonomists when deciding whether to recognize putative new species.

Study System

Protium heptaphyllum is distributed in most of all Neotropical biomes, across a wide range of climatic and environmental conditions.  This group exhibits a remarkable variation of leaf shape, flower and fruit traits and I aim to detect the informative characters to resolve its taxonomic delimitation. 

Protium is a diverse clade (ca. 160 species) that has undergone rapid diversification in the Neotropics (Daly et al., 2012; Fine et al., 2014) and includes many cases of cryptic speciation. A good example is Protium heptaphyllum (Aubl.) Marchand, one of the most dominant trees in the Amazon (ter Steege et al., 2013). Protium heptaphyllum sensu lato is very variable in terms of vegetative and reproductive traits. There are already named subspecies yet no consensus on the degree to which phenotypic variation corresponds to these taxonomic entities. Protium heptaphyllum sensu lato thus represents a promising study system to apply integrative taxonomy.

questions

My dissertation aims to explore the following questions: 1) Are Protium heptaphyllum sensu lato and closely related lineages reciprocally monophyletic? If not, how many putative new species a hyperdominant taxon could represent? Which lineages are dominant and which are not? After estimating the phylogenetic relationships among populations and revisiting the species hypothesis, I aim to test if putative species are also supported by morphological and leaf infra-red spectral evidences. Additionally, most hyperdominant trees are restricted to only one habitat type and often have congeners established in adjacent habitats. 2) However, how does habitat specialization evolve? Does lineage divergence occur across local ecotones? If yes, I aimed to unveil which traits have been selected for across different habitats? Finally, 3) how does demographic history explains radiation of different lineages and what does it tell us about the relative importance of climate, soil, and functional traits (including chemical defense)? Can NGS techniques give us additional information about the timing and processes of lineage divergence? In order to tie all the pieces of my dissertation together, I expect to reveal the extent to which habitat specialization is mediated by the expansion of population sizes and successive founder-events leading to divergence of novel plant lineages. 

RESULTs OUTLINE

  • Based on integrative taxonomy,  the hyperdominant taxon Protium heptaphyllum should be stated as multiple taxonomic entities because populations represent distinct monophyletic lineages with low genetic admixture and unique morphology. 
  • Protium cordatum, previoulsy circumscribed in Protium heptaphyllum, is reinstated as a closely related outroup based on high-throughput molecular sequencing data (Submitted to Taxon). 
  •  Based on the leaf economic spectrum data, functional traits can be as variable within a single species or taxon as across species.
  • The ability to physiologically acclimate along local ecotones favored the expansion of P. heptaphyllum’s populations over a wide range of habitat types in the Neotropics.
  • Once populations became geographically isolated, genetic structure was triggered in response to low gene flow and reproductive isolation between distant populations.
  • Our results speak directly to recent controversies regarding the “hyperdominance phenomenon” in the Neotropics. If we ignore that dominant clades may include many different putative new species, we will seriously underestimate the diversity of tree species and make large errors predicting the relative abundances of plant communities in the Neotropics.
  • Our findings highlight the importance of using multiple lines of evidence in taxonomy to improve our description and estimates of biodiversity in the tropics.

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