Sex allocation and reproductive success in a hermaphroditic perennial herb: both size and timing matter

In simultaneous hermaphrodites, resource availability and the temporal distribution of mates determine male and female fitness and optimal sex allocation. In insect-pollinated plants, we expect individuals to allocate more to their female function when they are large, and more to their male function when other individuals have many ovules available to be fertilized. We here studied the dependence of sex allocation and male and female components of reproductive success on both the size and the timing of reproduction in the plant Pulsatilla alpina (Ranunculaceae), accounting for variation in the mating system and inbreeding depression. Female reproductive success depended positively on size, whereas male reproductive success depended on mate availability and the timing of flowering, as predicted. Moreover, male reproductive success was trending to a saturating function of allocation to stamens, whereas female reproductive success was a slightly accelerating function of pistil production. These results provide new insights into the reproductive strategies of perennial plants and help to explain the joint strategy in P. alpina of andromonoecy (the production of both male and bisexual flowers by individuals over the course of their lives) and gender-diphasy (a shift between a male- and a hermaphrodite-phase among seasons).