Factors affecting intraplant variation in flowering and fruiting in the gynodioecious species Hebe subalpina

To determine the degree of variation in flowering and fruiting among shoots within naturally growing plants of the gynodioecious shrub Hebe subalpina, flower and fruit production were measured on both sexual morphs. Flower number varied within plants on both morphs, but while fruit production was just as variable as flower number within female plants, fruit production was more variable than flower number within the 'male' (or perfect-flowered) morph, which produced fewer fruits on average. A variety of shoot characteristics was also measured, to determine whether the variation in flowering and fruiting was related to differences among shoots in their resource status and/or hierarchy within the plant. Differences were observed between the morphs in the following respect: flower production within a shoot was correlated with shoot characteristics in both morphs, but fruit production was correlated with these variables only within male plants. Two experiments that altered shoots status (leaf and inflorescence removal) and one experiment that altered shoot hierarchy (terminal shoot removal) were performed on a limited number of shoots per plant (< 1%), to test directly whether these shoot characteristics were controlling fruit production within male plants. Fruit set and growth were reduced by leaf removal and fruit set was increased by inflorescence removal, confirming that shoot status affects fruit set and also that most of the resources available for reproduction come directly from within the shoot. However, an increase in both fruit set and growth in response to an increase in a shoot's hierarchical rank showed that some of these resources come from beyond the shoot. These results suggest that the age at which investment is adjusted differs for the two morphs and support the idea that the two morphs have evolved different resource allocation strategies.