SEX-RATIOS, SIZE DISTRIBUTIONS, AND SEXUAL DIMORPHISM IN THE DIOECIOUS TREE ILEX-AQUIFOLIUM (AQUIFOLIACEAE)

Sex ratio and sexual dimorphism in physiology and growth were studied in the dioecious tree Ilex aquifolium at two localities in northern Sp ain. Genet sex ratio was significantly male biased in one locality but not in the other. However, ramet and flowering ramet sex ratios were male biased at both study sites. Males had significantly thicker main trunks than females in one locality and produced more ramets in the ot her. Growth rate, estimated from mean width of annual rings, did not d iffer between localities, but males produced wider rings than females at both sites. Mean annual growth rates over the last 10, 20, and 30 y r were significantly higher for males. Measurements of chlorophyll flu orescence indicated that the efficiency of photosynthesis of leaves on nonfruiting branches of females was higher than for leaves on branche s of male plants under low-light conditions, though not under saturati ng-light conditions. Efficiency of photosynthesis was significantly lo wer on fruiting branches of female plants than on nonfruiting branches . We discuss whether the observed between-sex differences are attribut able to the higher cost of reproduction in females and/or to pollen co mpetition.