Julia Stutzman

Document Type

Honors Project

First Advisor

Dr. Timothy Kreps

Second Advisor

Dr. Justin Williams

Degree Award Date

Fall 2007


pollen, ovule, seed, pollen-ovule ratio, clutch size, latitude, Apocynaceae


Biology | Plant Breeding and Genetics | Plant Sciences


Pollen-ovule ratios have been used in numerous studies to determine breeding systems and pollination syndromes in flowering plants. These ratios have been shown to predict the type of reproduction ( self-fertilization or outcrossing) and the method of pollination ( wind, insects, etc) for many species of plants. Pollen-ovule ratios, however, have not been studied to determine if these ratios are subject to any spatial trends in fecundity, particularly the influence of latitude. Clutch size, or the number of eggs per reproductive effort, can be used to refer to the number of ovules or seeds per flowering effort in a plant. A very minimal number of studies have been done involving clutch size in plants. The research done by Levin and Turner with Asteraceae is the only research known to have involved latitude in clutch size assessment. Numerous studies of animals have shown that litter and clutch sizes increase with increasing latitude. These increases would be the equivalent of an increase in the number of ovules in a flower resulting in a decrease in pollen-ovule ratios at higher latitudes. The research presented in this paper is based upon an analysis of pollen-ovule ratios and clutch size in the Apocynaceae in relation to latitude. A total of 45 species were analyzed for the clutch size assessment and 17 for the pollen-ovule ratio. The results indicate that there is a significant fecundity trend present. Clutch sizes significantly increased with increasing latitude, resulting in a significant decrease in the pollen-ovule ratio at higher latitudes. Future studies will focus on filling in latitudinal gaps in the data to strengthen the statistical results. This research will hopefully spark interest into this area and promote further studies in different plant families to determine if this trend is a kingdom-wide event. 2