Diversification and specialization of orchid bees and their orchid hosts.

摘要

Mutualisms between flowering plants and their insect pollinators have played a central role in the evolution of modern terrestrial biodiversity. Specialized plant-pollinator interactions provide unique opportunities to study co-adaptations, speciation and diversification. However, few studies to date have taken a phylogenetic and comparative approach to investigate the evolutionary trajectories of the lineages engaged in such interactions. In the New World tropics, male orchid bees (∼200 species) actively collect chemical fragrances from orchid flowers, store them in specialized hind leg pockets, and subsequently present them to females during courtship. In so doing, male bees act as the exclusive pollinators of ∼700 species of orchids by vectoring their pollinaria. Here, I use multiple approaches to analyze the evolutionary dynamics of this mutualism. In Chapter 1, I contribute to the systematics of the species-rich genus Euglossa by describing three new species. In Chapter 2, I use a combination of phylogenetic and molecular clock methods to infer patterns of evolutionary diversification in euglossine bees. In Chapter 3, I describe the first known fossil orchid from a pollinarium attached to the mesoscutellum of an extinct stingless bee preserved in Dominican amber, and I use its age to date the origin of the family Orchidaceae. In Chapter 4, I reconstruct the evolutionary history of the euglossine-orchid mutualism by comparing phylogenetic trees of euglossine bees with those derived from orchid pollinaria. Finally, I use comparative methods to analyze the evolution of male fragrance collection in 15 sympatric closely related species of the genus Euglossa. Overall, these results contribute to the fields of molecular phylogenetics, taxonomy, systematics, paleontology and chemical ecology; collectively, they add to our understanding of the evolution of free-living mutualisms.