1. Low pollination intensity may cause low seed set in plant populations and is thought to be responsible for evolutionary transitions from outcrossing to selfing, or from animal to wind pollination. Variation in pollination intensity may also affect seed quality both through its influence on the degree of pollen competition (with lower quality offspring produced under low pollen intensities) and through seed size-number trade-offs (with plants under low pollination intensity producing fewer but larger seeds).
2. Here, we use a field experiment to examine the effects of pollination intensity on both quantity and quality of progeny. We manipulated pollen receipt to stigmas of the wind-pollinated dioecious plant Mercurialis annua by varying the distance of females from males. We then compared seed size and number, seedling growth and allocation to male and female function, for the progeny produced by females subjected to different pollination intensities.
3. Our experiment revealed a reduction in pollen load with increasing distance to males, translating into large reductions in the number of seeds produced but only small effects on the performance of offspring. The main effect on offspring quality was through a seed size-number trade-off, with pollen-limited females producing fewer but larger seeds, which subsequently performed better. Sons and daughters were affected differently by this trade-off, pointing to gender-dependent effects of pollination intensity on progeny performance.
4. Synthesis. Our results highlight the importance of pollination intensity on both the quantity and quality of progeny. Nevertheless, fitness calculations suggest that the enhanced quality of seed produced by pollen-limited mothers was not sufficient to offset their losses in terms of quantity.