Date of Award

5-2020

Degree Type

Thesis

Degree Name

Departmental Honors

Department

Biology

First Advisor

Noelle Beckman

Abstract

Secondary metabolites are chemical compounds that are considered to mediate a variety of plant interactions with their environment and are not involved in basic metabolism. Recently, there has been an interest in understanding the function and allocation of these metabolites in fruit tissues. In contrast to leaves, the chemistry in fruit tissue mediates exclusive interactions with seed dispersers that directly affect plant fitness and are under different evolutionary selective pressures. Only a few studies outline the patterns of chemistry between fruit and leaf tissues. This study aims to understand how secondary metabolites in two species of the hyperdiverse congeneric genus (Psychotria) differ between fruit and leaf tissues within each species, how plant tissue chemistry differs across species, and what implications this has for ecological interactions, seed dispersal, and the understanding of evolutionary processes. Plant samples from seed, leaf, and pulp tissue were collected from two species of the hyperdiverse Psychotria genus, P. marginata and P. limonensis. Plant samples were collected in a Neotropical forest on Barro Colorado Island in Panama. The secondary metabolites from these plant tissues were extracted using a [99.9: 0.1] ethanol to formic acid solution. The plant extracts will be analyzed using liquid chromatography coupled with mass spectrometry methods. The data will then further be analyzed using novel modeling methods to elucidate and compare the chemical structural diversity of each tissue and species.

Within species, I predict the chemical makeup of leaf tissues is different than that of pulp and seed tissues. This would further support the hypothesis that secondary metabolites in fruit tissues have an adaptive function. Across species, I predict that the differences in secondary metabolite diversity in leaf tissues will be greater than the differences within species. These results would suggest an evolutionary mechanism in which defensive leaf chemistry is selected upon. This selection of leaf chemistry contributes to the diversification of the genus to fill novel niches and allows for the hyperdiverse genus to coexist within a small area. Though the chemistry between the leaf tissues is predicted to be divergent when compared across species, the question remains if this trend will be exhibited in fruits. I predict that fruit tissue chemistry will be similar between species in order to conserve the important function these metabolites play in mediating interactions with the same seed disperser within the genus. This study will lead to a better understanding of the evolutionary selective processes imposed on different plant tissues and the significance that these metabolites play in the diversification of plant genera.

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Biology Commons

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