Date of Thesis

Summer 2018

Thesis Type

Masters Thesis (Bucknell Access Only)

Degree Type

Master of Science

Major

Biology

First Advisor

Christopher Martine

Keywords

Solanum, andromonoecy, dioecy, pollen grains, amino acids, proteins

Abstract

Dioecy has arisen several times in Solanum, each time presenting as a morphologically androdioecious breeding system rendered functionally dioecious by the production of inaperturate pollen in morphologically bisexual flowers. The inaperturate pollen produced by functionally female flowers is unable to germinate but is likely retained because pollen represents the only pollinator reward produced in Solanum flowers adapted for buzz pollination. While comparisons of exine morphology have been made between aperturate (produced in staminate flowers) and inaperturate grains, little has been done to compare biochemical composition as a means to evaluate the potential for differential nutritive rewards depending on flower type. For that reason, we studied the nutritional values of pollen by estimating the differences in amino acids and total protein concentrations between the two pollen types (aperturate and inaperturate pollen) in three dioecious Australian taxa: S. sejunctum, S. ossicruentum, and S. asymmetriphyllum. These analyses will help us to understand the ecological and evolutionary significances of the nutritional values of pollen grains in the Australian Solanum species and their pollinators. We also compared these to the pollen from hermaphrodite and staminate flowers from a related andromonoecious taxon, S. ultraspinosum. We extracted proteins with a modified phenol extraction protocol and used a hydrolysis method to quantify the total amino acids along with a profile of total and free amino acids. Our results for the dioecious species show that proteins and amino acids in aperturate pollen grains from staminate flowers have significantly higher levels than inaperturate pollen grains from functionally carpellate flowers of these species. These results suggest a greater level of nutritive reward for pollen foragers for aperturate pollen issued from staminate flowers of functionally dioecious Australian Solanum species. The highest levels of reward, however, were found in the hermaphrodite flowers of the andromonoecious study species, perhaps because of their origin as "leaky males" and the consequent investment in male sexual function.

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