Reproductive biology of Agalinis skinneriana (Scrophulariaceae), a threatened species

Agalinis skinneriana is a rare, autogamous, bee-visited, annual plant native to the Illinois prairie. Two populations differing in size were chosen for study: the Site M population with thousands of individuals and Revis Hill Prairie population with only hundreds of individuals. These populations were found to differ significantly in their potential for autogamous selfing. In bagging experiments, the Revis population had a potential selfing rate of 99% compared to 85% at Site M. The higher potential far autogamous selfing in plants at the Revis population was associated with a small population size, no observed bee visitors, a larger ovary, increased proportional biomass to the gynoecium, lower pollen viability, reduced pollen production/flower, and a lower P/O ratio compared with plants at the Site M population. The data suggest that autogamous pollination in A. skinneriana has evolved as a mechanism to assure reproduction as a result of habitat destruction and fragmentation and subsequent small population size.