Sexual dimorphism in the timing of flowering in two dioecious trees in a subtropical wet forest, Puerto Rico

Abstract

In dioecious plants, sexual selection can promote the evolution of differences in the flowering display of males and females. Theory indicates that male reproductive success is principally limited by the number of mates, while female reproductive success is principally limited by resources invested in fruit production. Consequently, male-male competition may result in earlier and prolonged flowering displays of males, while females should flower later than males and exhibit shorter flowering displays because they need to optimize available resources for fruit production. Here, we report sexual differences in the time of flowering of Cecropia schreberiana and Dacryodes excelsa, two dioecious trees native to Puerto Rico. We interpret our results in the context of sexual selection and potential pollen limitation. Timing of flowering was estimated by direct observations of the trees during flowering and by using flower and seed records of a long-term phenology study. Our results show that males of both species tend to exhibit earlier and more prolonged flowering displays than females. In addition, more than 70% of male and female reproductive activity of both species was prolonged, lasting more than six consecutive months. We propose that prolonged flowering periods working in conjunction with other ecological traits associated with dioecy in plants might help to reduce the effect of pollen limitation on reproductive success.