Associate Professor of Biology University of Michigan-Dearborn, United States
Abstract: The linear, leguminous fruits of honey locust, Gleditisia triacanthos L., vary extensively in length, mass, and shape. The purpose of this study was to examine the effects of seed and fruit packaging on the dispersal dynamics of honey locust fruits. Fruits were sampled from trees growing at three sites (Dearborn, Dearborn Heights, and Ypsilanti) in southeastern Michigan. Fruit dimensions, mass, and shape were assessed to determine whether differences in fruit structure were associated with differences in dispersal ability. A dispersal experiment was conducted in which all fruits were released from a platform with a fixed height of 10 m aboveground, and their time and distance of dispersal were measured. The fates of individual seeds within fruits were subsequently determined when the fruit contents were examined using light microscopy. We found that the frequency distribution of honey locust fruit dispersal distance was positively skewed, with 99% of fruits falling to the surface of the ground within 10 m from their point of release. Dispersal time and distance were significantly related to fruit mass. Smaller, lighter fruits travelled greater times and distances than did larger, heavier fruits. Differences in fruit mass were the product of non-random patterns of seed maturation and abortion within fruits. Whereas the probability of seed maturation within individual fruits decreased significantly from the distal to basal ends, the probability of seed abortion increased significantly. However, average seed mass did not differ significantly with seed position within a fruit. Hence, our study suggests that the maternal regulation of seed fate may be a mechanism for optimizing dispersal ability of honey locust fruits.
