REU: Effects of Seed Dispersal on Fitness in a Forest Shrub

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A crucial, but poorly known, force affecting the genetic structure of natural populations is dispersal. For most organisms, it is difficult to trace an individual once it leaves its place of birth, and even more rarely do we know what factors will determine whether or not the individual survives or successfully reproduces. The problem of tracking a dispersing individual is especially difficult in the case of plant seeds which are swallowed by fruit-eating animals. It is virtually impossible to be sure where the seeds of a particular parent plant are deposited, because an animal often eats many fruits from a variety of plants and may defecate them over a long time span. This study is designed to track seed dispersal in a North American shrub, the spicebush (Lindera benzoin) by turning the usual question backwards: where are the parent plants of seeds that are deposited in known locations? The seed-producing parent of a given seed can be identified by matching up patterns of genetically-determined proteins. Experimental plantings of seeds will then show how important it is to seedling survival for seeds to be deposited far away from other spicebush seedlings, away from the nearest spicebush adult, or in shady versus sunlit conditions. The answers to these questions will reveal how seed dispersal affects the genetic mixing of this plant population, how effective animal dispersers are in depositing seeds in sites beneficial to spicebush plants, and what characteristics of individual plants favor high reproductive success. These basic results in turn can be used in management plans for preserving isolated plant populations in which dispersal is artificially restricted.