Collaborative Research: Comparative Breeding Structure of Four Species of Sonoran Desert Columnar Cacti

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9421673 FLEMING The Sonoran Desert is the lushest, most species-rich desert in the world. Conspicuous among its uniquely drought-adapted plants are four species of columnar cacti: saguaro (Carnegia gigantea), organ pipe (Stenothereus thurberi), senita (Lophocereus schottii), and cardon (Pachycereus pringlei). These species often occur in high densities, represent much of the living plant biomass in their communities, and serve as sources of food (nectar, pollen, fruit, and seeds) and shelter for a large number of desert animals. Despite the obvious ecological their reproductive biology and the importance of different kinds of pollinators for their reproductive success. In this study, we will conduct experiments to document the relative contribution of bats, moths, birds, and bees to the pollination success of columnar cacti and will analyze the genetic composition of seeds in the fruits produced by these pollinators. Our overall goal is to understand how different kinds of pollinators affect the genetic structure of populations of their food plants. Studies of the breeding system of desert plants are of particular importance because their extremely episodic recruitment (cactus populations gain new individuals in only one year in ten, on average) can have long-lasting effects on the genetic composition of individuals in their populations. Thus, the examination of four species of columnar cacti whose flowers are visited by different combinations of bats, birds, and insects will serve as a model system for studies of pollination biology as well as provide new insights into the processes that shape the genetic diversity of desert plant species. Our study will be the most detailed picture of the contributions of different kinds of pollinators to the breeding systems of flowering plants to date. Such knowledge is critical if we are to understand the role of pollinators in plant speciation, the origin of plant-pollinator interactions, and the potential genetic consequences to plants o f the loss of pollinators through human disturbance.