A field investigation of the environmental factors associated with explosive seed dispersal in the dwarf mistletoe Arceuthobium Americanum

Dwarf mistletoes (DMs), genus Arceuthobium, are dioecious, flowering plants with a broad geographical distribution. More specifically, they are obligate aerial parasites that utilize members of Pinaceae and Cupressaceae for water, carbohydrates, and other nutrients, and are rooted to their host by an extensive endophytic system. On the host’s surface, DM are characterized by reproductive shoots that are drastically reduced in size and, on the female plant, develop bicoloured fruits (Hawksworth and Wiens 1996). Arceuthobium americanum, a North American species of DM, is parasitic on lodgepole pine trees throughout British Columbia (Geils et al. 2002). Like almost all DMs, the seeds of A. americanum are dispersed through an explosive mechanism in which the rupture of mature fruit expels the seed from the parent plant. The sticky coating of viscin cells allows these seeds to adhere to the new host trees on which they land. This dispersal phenomenon occurs in the early fall, while germination of the new DM does not ensue until the following spring when light, temperature and moisture are suitable (Hawksworth and Wiens 1996, Geils et al. 2002). Several years of endophytic growth occur before reproductive shoots become apparent, and at least one to two more years of growth occur before flowering takes place. Following pollination via wind or insects, another year elapses before the fruit mature and explode in the early fall (Geils et al. 2002). Although their prolonged lifecycle does not allow for rapid forest infestations, DM’s dependence on its host detrimentally affects forest productivity. Infections decrease the quality of host wood, weaken the immunity of the trees against other diseases, and ultimately shorten the lifespan of the trees (deBruyn et al. 2015). Furthermore, the branches of the trees infected by the DM become dry and brittle, which poses a major forest fire hazard. Forestry industries suffer extensive losses due to the decreased wood quality resulting from DM infections (Geils et al. 2002). Increasing our understanding of how the DM disperse could give foresters insights into controlling these independently dispersing parasites. The purpose of this study was to investigate whether there are any weather variables, such as temperature and humidity, associated with the seed dispersal mechanisms of lodgepole pine DM, and comprised three main objectives. The first objective was to determine the weather pattern of the field site by recording environmental variables using a weather station. The second objective involved tracking the pattern of fruit loss over a chosen set of sample DMs, determined by analysis of daily photographs of 11 samples and time lapse footage of one sample, from which light-intensity information was also obtained. Lastly, the data resulting from the first two objectives were combined to accomplish the last objective; namely, to determine if there are significant relationships between fluctuations and trends in the weather variables, and the occurrence of fruit explosions throughout the dispersal period.Not peer reviewedSupervisors Dr. Cynthia Ross Friedman & Dr. Mark Paetka