REPRODUCTIVE ALLOCATION AND RESOURCE COMPENSATION IN MALE-STERILE ANDHERMAPHRODITIC PLANTS OF PLANTAGO-LANCEOLATA (PLANTAGINACEAE)

Gynodioecy is a breeding system in which hermaphrodites coexist with m ale steriles. Theoretical models predict that without any compensation in female fitness male steriles will disappear from a population due to their reproductive disadvantage. In the present study I investigate d whether male-sterile (MS), partially male-sterile (IN), and hermaphr oditic (H) plants of Plantago lanceolata differed in reproductive grow th and allocation. Offspring of three interpopulation crosses segregat ing all three sex morphs were grown under nitrogen-limited conditions in a growth chamber, Independent of the genetic background MS plants a ttained a higher vegetative and reproductive dry mass and a higher rep roductive output than H plants, whereas IN plants had intermediate val ues. When corrected for the mass of the pollen, the dry mass differenc es between the sex morphs were much reduced but still present. However , when H hole-plant allocation was expressed on the basis of nitrogen, the differences between the sex morphs disappeared. Thus the sex morp hs took up similar amounts of nitrogen but distributed them differentl y. The MS and IN plants used the nitrogen saved by net producing polle n for additional vegetative as well as reproductive growth. The data p resented in this study suggest that resource compensation is one of th e main mechanisms responsible for the maintenance of MS and IN plants in gynodioecious P. lanceolata.