Sex ratio variation in dioecious plant species: A comparative ecological study of six species of Lindera (Lauraceae)

Abstract

Sex ratio variation was investigated in natural populations of six dioecious shrub species of Lindera in Japan. Interspecific differences in sex ratio were examined in relation to patterns of population structure, floral dimorphism, fruit production and intersexual differences in herbivory. Sex ratios tended towards equality or bias in favour of males, except for populations of L. glauca, in which no male plants were found. Sex switching in individual plants was not observed. Although male flowers were generally larger in size than flowers of conspecific females, costs of flowering did not appear to influence sex ratio. However, a relation was found between high allocation to fruit production and increasing male fraction of populations. In addition, girths of flowering plants tended to be larger in females, which may indicate delay in age of the first reproduction compared to males. No intersexual difference was found in degree of leaf damage due to herbivory. Results of this study are discussed in the light of other studies on sex ratio variation in dioecious plant species.