Sex-Specific Flowering Patterns and Demography of the Understorey Rain Forest Tree Iryanthera Hostmannii (Myristicaceae)

Abstract

Sexual dimorphism in dioecious plants is a common phenomenon that has received widespread attention, yet the implications for reproductive function and fitness remain poorly understood. Using data from a long-term study of a population of 839 dioecious Iryanthera hostmannii (Myristicaceae 'nutmeg') trees in a large permanent plot in a lowland tropical rain forest, we examined the effects of greater investment in reproduction by females compared to males for various aspects of life history. Although male trees often produced more inflorescences than females, total dry mass of flowers was roughly equal in two out of three years for both sexes, implying that any investment differential lies in fruit production. There was no difference in the 12-year relative growth rate of males and females, suggesting that females can compensate somehow for their greater reproductive investment, although there were weak suggestions that mortality might have been greater in females. Male flowers opened slightly earlier in the day than female flowers and were short-lived, lasting at most two nights compared to up to four nights in females. Understanding the interacting effects of resource availability (studied here) and pollen movement (currently unknown in Iryanthera) on reproduction is essential in terms of life history theory. Knowledge of reproductive biology is key in considering the ecology and conservation of tropical forest communities.

Phenological Strategies of Dioecious Species in Response to the Environmental Variations of Rupestrian Grasslands

“…In dioecious species a big exposition of male flowers and the chick-pollen is related to the increase in the flowering time BAWA, 1981;MUNGUIA-ROSAS et al, 2011), thus increasing the pollination capacity (QUEENBOROUGH et al, 2013;MATSUHISA;USHIMARU, 2015), while females only need the period necessary to receive the pollen grain to ensure the production of seeds (OTÁROLA et al, 2013), presenting shorter and more intense capacity (MATSUHISA; USHIMARU, 2015) The flowering in dioecious individuals tends to present distinct occurrence time between male plants and female plants (MUNGUIA-ROSAS et al, 2011;MATSUHISA;USHIMARU, 2015). The female flowering is delayed and synchronized with the peak intensity of male plants and an earlier male flowering was associated with the competition among individuals of the population for greater dispersal of gametes and consequently, their characters (BULLOCK; BAWA, 1981;GRANT, 1995;MUNGUIA-ROSAS et al, 2011;QUEENBOROUGH et al, 2013;MATSUHISA;USHIMARU, 2015). Female flowers support longer flowering cycle, maintaining a longer lasting bloom in relation to male flowering (ESPÍRITO-SANTO et al, 2003;MATSUHISA;USHIMARU, 2015), explained by the need for longer visits by pollinators.…”

The potential risk of tree regeneration failure in species-rich Taba Penanjung lowland rainforest, Bengkulu, Indonesia

“…Such a process requires both the synchronization of flowering phenology and the presence of pollinators, which could lead to uncertainty on seed production and tree regeneration. The uncertainty is even greater because the sex ratio of dioecious species is malefavored (Queenborough et al 2009;Gao et al 2012), and male flowers bloom earlier than their female opposites at certain species (Queenborough et al 2013).…”

Phenology of Sclerocarya birrea (A. Rich.) Hochst. Provenances

“…The results also revealed variations in period of flower bud initiating and opening between provenances. The earlier flowering in males of S. birrea is associated with the competition among individuals of the population for greater dispersal of gametes while delayed flowering in females enabled them to synchronize with males at the peak of their flowering intensity for increased pollination [10,23,24]. The longer period from bud to anthesis in males suggest that males requires longer period for pollen development for increased pollination capacity while females need shorter period for pollen reception to ensure seed set [24].…”