Maternal regulation of fecundity: non-random ovule abortion inCassia fasciculata Michx.

We examined the extent of ovule abortion and the within-fruit pattern of abortion inCassia fasciculata, an annual legume, and tested the hypothesis that abortion can result from competition for limited maternal resources among developing fruits and seeds. In a natural population at Mayview, IL, 53.4% of ovules in mature fruits matured as seeds; 43.4% showed some development but aborted, and 3.1% showed no development over virgin ovules. In a greenhouse experiment in which treatments were applied after most fruits were initiated, nutrient addition and partial root removel had no effect on abortion, but drought reduced the proportion of ovules maturing to 75% of the control mean. A fruit thinning experiment was conducted in which the number of fruits initiated on certain plants was limited. Control plants had more ovule abortion than fruit-thinned plants, suggesting that abortion resulted from competition for limited maternal resources. A "position effect" was observed in both field and greenhouse populations; ovules toward the fruit base (pedicellar end) had higher frequencies of abortion than those at the distal end. Thus, ovule abortion, like fruit abortion in this species, is non-random. Indivisuals regulate fecundity at both the whole fruit and individual seed levels.