Relationships among fragrance, phylogeny and pollination in southwestern Nyctaginaceae

Abstract

Fragrances appear to act in conjunction with visual cues to attract specific pollinators. Besides the ecological influence of pollinator type on fragrance, as with many other attributes of organisms, phylogenetic history may also affect fragrance composition. In this dissertation I examine the quality and quantity of floral and vegetative fragrance, and explore the relationships among fragrance, pollinators, and phylogenetic history in the plant family Nyctaginaceae. Using DNA sequence data, I inferred phylogenetic relationships among and within the Nyctaginaceae genera Acleisanthes, Selinocarpus, and Mirabilis. There is a high incidence of hawkmoth pollination within these genera, in addition to multiple pollinator transitions. Results suggest that neither Acleisanthes nor Selinocarpus are monophyletic, but that together they comprise a monophyletic lineage. Because of this finding, I have taxonomically combined these two genera into a single genus. Analyses of floral and vegetative fragrance from Acleisanthes, Selinocarpus, and Mirabilis species included in the phylogenetic study show that each species has a unique fragrance profile. Further, although there is substantial variation among individuals within species, intraspecific variation is significantly lower than interspecific variation in fragrance profiles. Fragrances are composed of 5--108 different compounds from at least seven different biosynthetic classes. Some species produce most of their fragrance vegetatively, while floral emissions are the sole source of volatiles in other taxa. Results show that neither total amount of volatiles nor the amount of floral volatiles per mug floral tissue is correlated with pollinator type. However, the emission of nitrogen-bearing compounds appears to have been lost in those lineages that have also lost moth pollination, suggesting that the presence of nitrogen-bearing compounds may be important for moth attraction. Although the phylogenetic signal in the fragrance data is not entirely congruent with the signal in the DNA sequence data, certain compounds and biosynthetic pathways do support the independent phylogeny inferred using the DNA data. However, it is also clear that many compounds are highly homoplastic, yielding limited phylogenetic information. Overall results suggest that phylogenetic relationships rather than pollinator affinities are better predictors of fragrance composition among these Nyctaginaceae species.