Evolution of Syagrus Palms and Their Insect Pollinators

Abstract

Plants and their specialized flower visitors have provided valuable insights into the evolutionary consequences of species interactions. However, only a small fraction of the existing diversity has been studied in depth, and the discovery of novel systems brings the potential of new ideas and means of testing hypothesis. In this dissertation I study a known but overlooked tropical community: palm trees and their specialized insect flower visitors. In Chapter 1, I test whole genome amplification as an alternative for high-throughput DNA sequencing of small organisms such as insects. I evaluate potential biases and find that it yields adequate data for population genetic analyses. Chapter 2 introduces the study system: the licuri palm Syagrus coronata and its flower visitors. I review the literature and make new observations showing that this plant is pollinated both by generalist bees and by specialized beetles that breed on seeds and fruits. This diverse community also includes many non-pollinators, ranging from antagonists damaging flowers to commensals feeding on decaying plant tissues. In Chapter 3, I study the phylogeography of the licuri, and find that populations are isolated by distance but not by differences in environment. There is widespread hybridization with closely related palm species and in a lesser degree with more distant relatives. In the latter case, co-occurence is more important than sharing specialized beetle pollinators. Finally, in Chapter 4 I use a comparative approach to test the role of insect-host interactions in the presumed early stages of diversification of beetles associated with Syagrus coronata and Syagrus botryophora. I find a surprising number of cryptic species, which coexist across a broad geographical range for pollinators but not for non-pollinators. Insects previously thought to be associated with both plants turn out to be different species or highly diverged populations. In contrast, the degree to which insect populations are structured by divergence of host populations varies. This variation is uncorrelated to the mode of interaction, showing that, at least in this system, plant spatial deployment is of greater potential relevance to any insect than the mode of its interaction with the host.