When flowers of the self-compatible herb Mirabilis jalapa are pollinated with either self or outcross pollen randomly over the entire plant, there is no selective abortion of selfed fruits or seeds, or any evidence of inbreeding depression. We tested the hypothesis that when developing selfed and outcrossed fruits are in close proximity to each other and in direct competition for resources, there will be an increase in the abortion of selfed fruits and in the expression of inbreeding depression. This was done by performing clustered pollination treatments, such that all flowers on a branch either received all self pollen, all outcross pollen from a variety of donors, or flowers within a cluster were alternately pollinated with self or outcross pollen. We predicted that differences in rates of abortion, seed size, and/or seedling vigor would be greatest between selfed and outcrossed treatments on mixed clusters. Pollination treatment and cluster type had no influence on rates of abortion or seed size. Germination and seedling performance were not different for self and outcross treatments for unmixed clusters; however, outcrossed seeds and seedlings significantly out performed those from self pollinations from mixed clusters. This suggests that when developing in close proximity and potentially competing for resources, outcrossed seeds have an advantage over selfed seeds, but this advantage is not observable until later in the plant’s life-cycle when seeds are planted in the field.

Key words: inbreeding depression, Mirabilis jalapa, resources, selective abortion, self pollination