Reproductive investment in male and female <i>Eurya japonica</i> (Theaceae) at tree and branch levels

Abstract

Intersexual differences in reproductive investments (RIs) (dry mass of reproductive tissue) at tree and branch levels in Eurya japonica were examined during two successive years. Mean total RIs per tree for males and females (adjusted for the mean trunk diameter in the combined sample trees, 25.7 mm) were 3.47 and 5.67 g dry mass. Females generally allocated about 1.6 times more biomass per tree to reproduction than males. On the other hand, male total RI per terminal branch averaged 51.6 mg dry mass and female averaged 226.6 mg. Females generally allocated about 4.4 times more biomass per terminal branch to reproduction than males. Thus, the magnitude of sexual difference at the tree level was much lower than that at the branch level. There were negative correlations between interyear fluctuation of total RI and stem diameter for both sexes. Interyear fluctuation of RI was greater for females than males in all size categories. This study revealed that conclusions from tree measures of RI differed from branch measures and suggested the importance of evaluating the average RI at the tree level for woody plants. I discussed the importance in adopting an effective sampling strategy for evaluating the RI at the tree level.