Effects of Inbreeding on the Male and Female Functions of Plants

Stephenson 9806691 Inbreeding depression is the reduction in fitness of inbred progeny (progeny resulting from self-pollinations or pollinations by close relatives) relative to outcrossed progeny. An impressive body of theory predicts that inbreeding depression is a major force in the evolution of floral traits (size, shape, color, odor, etc. of flowers) and mating patterns in plants. Over the past century many studies have shown that inbreeding reduces relative survivorship and the relative number and quality of the seeds produced by plants. However, most studies have ignored the effects of inbreeding on the male (pollen) function of plants despite the fact that most plants are hermaphrodites (produce both pollen and seeds). Moreover, we know little about how the magnitude of inbreeding depression changes with growing (environmental) conditions. Finally, there remains much debate concerning the genetic basis of inbreeding depression. Consequently, we will perform a series of projects designed 1) to quantify and compare the magnitude of inbreeding depression on survivorship and reproduction through both the male and female functions, 2) to examine the relationship between inbreeding depression and environmental stress, 3) to determine the relationship between inbreeding and fitness across four levels of inbreeding, and 4) to determine the proximate cause of inbreeding depression on the male function. The data obtained from the projects in this proposal will result in the first comprehensive study of the effects of inbreeding on the male function of plants; they will generate testable predictions (and the seeds necessary to test these predictions) concerning the genetic basis of inbreeding depression; they will allow us to better predict the direction in which floral traits will evolve under different environmental conditions; and they will allow us to critically evaluate the theory surrounding the evolution of plant mating patterns. From a practical perspective, our findings will have important ramifications for agriculture (e.g., the hybrid seed industry uses inbred lines of plants as the major component in their breeding programs), conservation biology (e.g., the preservation of endangered plants that now exist only in small, highly inbred populations), and forestry (where pollen selection is of utmost importance because traditional plant breeding techniques fail due to the long generation time of trees).