Gabriel Damascopeople.html

  My research interests are centered on understanding the origin of plant lineages and how communities are organized in tropical regions. While many studies have documented the extraordinarily high tree diversity in tropical rainforests, very few have investigated how this diversity has evolved. In my research, I will test the hypothesis that species-rich patterns in the tropics evolved due to habitat specialization through evolutionary divergence of dominant and widespread plant lineages. I predict to find that widespread dominance evolves first, and that habitat specialization evolves secondarily, due to tradeoffs in resource availability across habitat gradients. One way to study habitat specialization is to focus in a widespread habitat-generalist plant taxon that may be in the process of undergoing speciation. Protium heptaphyllum (Aubl.) Marchand is a promising model system because there is evidence that some differentiation has occurred (P. heptaphyllum subsp. cordatum; P. heptaphyllum subsp. heptaphyllum; P. heptaphyllum subsp. ulei), but it is certainly not complete, given the morphological variation within regions and habitats that do not easily fall into taxonomic categories. Populations of P. heptaphyllum are found in many different tropical habitats from Cuba to Paraguay (Figure 1). A phylogenetic reconstruction using multiple gene sequences from the genus Protium showed that different populations and subspecies of P. heptaphyllum do not form monophyletic groups. In addition, posterior probabilities did not reflect well-supported clades and more samples are necessary to solve the relationship among populations. Hence, we cannot rule out that what we are currently calling one species might represent divergent phylogenetic lineages. In my PhD project, I will use an integrative approach to understand the evolutionary history of P. heptaphyllum by investigating morphology, genetics, biogeography and ecology in order to understand the role of habitat specialization in the diversification of plant lineages in the Neotropics.

Figure. Distribution map of Protium heptaphyllum according to the New York Botanical Garden dataset (upper left). Evidence for flower color divergence among different sub-populations (trees in Central Brazil gallery forests have red/violet flowers; upper center). Examples of different habitat types where P. heptaphyllum was already sampled (bottom pictures).


Overall research goals:


       1) Confirm if P. heptaphyllum species complex is a monophyletic lineage.

Evidences from Fine et al. (in press) were not enough to reconstruct the phylogenetic relationship among different populations of this group. I will sample P. heptaphyllum populations across a wide range of ecosystems, including four main geographic subunits: Amazonia; Central Brazil Savannas; Guiana Shield; and Atlantic Coastal Rain Forests. Several populations have already been sampled from Amazonian white-sand forests during my Master’s degree at the National Institute of Amazonian Research (Damasco et al. 2013) and in collaboration with my advisor Dr. Paul Fine at the UC Berkeley and Dr. Douglas Daly at the New York Botanical Garden (Fine et al. 2010, Daly et al. 2012). However, collections from many important geographic localities, including localities where subspecies types and synonymies were found, are still lacking. Thus I plan to target this areas in my PhD to improve sample collection of these regions.


2) Perform a phylogeographic study of P. heptaphyllym subpopulations within and among different climatic regions and test if divergence in this species complex is an outcome of incipient speciation through habitat specialization.

Besides the widespread distribution, P. heptaphyllym is a habitat generalist along environmental gradients within Tropical biomes. For instance, in the Amazon, this taxon occurs in terra firme forests and also in white-sand forests; in Cerrado (Central Brazil), it occurs along gallery forests, savannas and seasonal dry forests; in Atlantic Coastal Forests, it occurs along costal rain forests and coastal white-sand (restingas) gradients. Along each of those environmental gradients, I will sample at least 15 individuals from each habitat type collecting fresh leaf material for genomic DNA extraction. In order to test for phenotypic plasticity and trait conservatism, we will also measure ecologically relevant functional traits (e.g. specific leaf area, xylem anatomy, leaf nitrogen content, leaf carbon isotope composition) as a way to understand how plants respond to their specific environmental niches. I aim to estimate genetic differentiation among subpopulations in order to test for gene flow between habitats and calculate effective population size and migration rates using Wright´s Fst and derived estimates. Directionality of population expansion and estimations for the center of origin for this plant lineage will be accessed by the ancestor geographic range reconstruction of lineages.


Our results will offer novel insights on how environmental heterogeneity can influence the evolution of tropical plants in the most botanically diverse region in the world. By combining habitat association data with estimates of population growth over time, I will be able to unravel the history of hyperdominance and habitat specialization in Protium heptaphyllum. I hypothesize that P. heptaphyllum lineages are undergoing incipient divergence and that adaptation to new habitats occurs subsequent to the evolution of widespread species and that habitat specialization thus plays a fundamental role in the generation of plant diversity in the Tropics.

 
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