SELECTIVE FRUIT FILLING IN RELATION TO POLLEN LOAD SIZE IN ALSTROEMERIA-AUREA (ALSTROEMERIACEAE)

We conducted an experiment in a natural population of Alstroemeria aur ea, a clonal perennial, to determine (1) if reproduction was resource limited, and (2) if fruits would be selectively filled based on differ ences in pollination intensity when pollen loads were adequate for ful l seed set. Under these conditions, differences in pollination intensi ty are unlikely to affect seed number, but could affect seed quality, providing an interesting test of the gametophytic competition hypothes is. To test for resource limitation, percent fruit maturation, number of seeds per fruit and average seed weight were compared to paired con trols for ramets in which all but one fruit was removed. To test the e ffect of pollination intensity on selective resource allocation, three types of pollination treatments were performed: (1) all flowers of th e single inflorescence received a low pollen load, (2) all flowers rec eived a high pollen load, (3) alternate flowers of the inflorescence r eceived either a high or a low pollen load. We determined the percenta ge of fruit that reached maturity, counted the number of seeds and ovu les and calculated the average seed weight for all capsules in each tr eatment. Resources appeared to limit reproduction in this population s ince seed number and weight were significantly higher than in controls when competing capsules were removed. At the whole ramet level, a fou r fold difference in pollen loads had no significant effect on any of the parameters measured. However, when pollination intensity varied wi thin an inflorescence, the number of seeds per fruit increased by abou t 10% in flowers that received the higher pollen load. We observed the same trend in each of 2 years, but the increase was significant in on ly 1 year. The differences,, although not great, were only slightly sm aller than when all competing fruits were removed, and were consistent with selective re source allocation based on pollination intensity in dependent of seed set.