SEX-DIFFERENTIAL RESOURCE-ALLOCATION PATTERNS IN THE SUBDIOECIOUS SHRUB HEBE-SUBALPINA

Vegetative growth and sexual reproduction were compared for the 2 sexual morphs of the subdioecious evergreen New Zealand shrub Hebe subalpina. Both morphs produced the same number of flowers, but because the flowers of the polleniferous morph ("males') are larger males allocated almost twice as much biomass to flower production as did females. Females produced larger fruit as well as more fruit. Females allocated 4.7 times as much biomass as males on fruit production. Overall, females allocated almost twice the biomass to flowers and fruit. The morphs also differed in the timing of their growth, each morph growing less during the phase in which its reproductive costs were highest. Despite the greater allocation by females to reproduction, the morphs grew the same amount over the entire reproductive cycle. This may be a result of the fact that females produced more leaves earlier in the season, which enabled them to accumulate more resources than males. Defoliated shoots on females fruited, but did not grow relative to controls, and defoliated shoots on males grew, but did not fruit. Differences suggest that divergent selection has been operating on the morphs since the evolution of subdioecy (via gynodioecy) from cosexuality, and may be related to differences in the relative fitness gains to the morphs through pollen vs. seeds. -from Author