Sexual Differences in Reproductive Phenology and their Consequences for the Demography of Baccharis dracunculifolia (Asteraceae), a Dioecious Tropical Shrub

Abstract

Patterns of phenological variation and reproductive investment were studied in the dioecious shrub Baccharis dracunculifolia DC (Asteraceae), and possible consequences on survivorship were evaluated. The sex ratio was determined in a natural field population (n = 921) of B. dracunculifolia in Belo Horizonte, Brazil. Fifty-two males and 56 females were sampled at random from this population. During the reproductive season of 1999, inflorescence production, shoot growth and mortality, and xylem water potential were recorded for each individual. The population sex ratio was male-biased (1.27 : 1, P < 0.05), and was associated with a higher mortality of female shoots (38.4 vs. 23.1 %, P < 0.05), and individuals (17.8 vs. 11.5 %, P < 0.1), despite lower water stress in female plants. Flowering phenology also differed between the sexes, with males producing more inflorescences, and earlier, than females. Owing to fruit maturation, the number of inflorescences supported by females was higher than that supported by males later in the reproductive season. This occurred during the dry season, and drought stress may have been responsible for the greater female mortality. Thus, the male-biased sex ratio in this population of B. dracunculifolia is probably due to different reproductive functions of males and females. Intersexual differences in reproductive phenology had consequences for plant demography.

Flowering phenology of Catopsis compacta (Bromeliaceae), a dioecious epiphyte in an oak forest

“…Height differences between female and male individuals are considered a product of differential resource allocation to vegetative processes (Espírito-Santo et al 2003, Barrett & Hough 2012. The lack of size differences between female and male individuals of Catopsis compacta may result from the limited supply of nutrients and water in the epiphytic habitat.…”

“…With respect to the difference in the number of flowers between female and male individuals, in dioecious species it is common for male plants to produce more flowers per individual than female plants (Bram & Quinn 2000, Espírito-Santo et al 2003, Munguia-Rosas et al 2011, Barrett & Hough 2012. Male plants allocate more resources to produce more flowers because their fitness is directly linked to the number of pollen grains released.…”

“…These costs are energetically expensive, dramatically more so for epiphytes considering the oligotrophic environment in which they grow (Benzing 1990, Espírito-Santo et al 2003, Amorim et al 2011.…”

Gender-Related Climate Response of Radial Growth in Dioecious Fraxinus mandshurica Trees

“…Greater precipitation in November indicates more snow on the forest floor during the winter months and thus increasing soil moisture during spring, which promotes radial growth during the following growing season (LaMarche 1974;Takahashi et al 2003). The cost of reproduction is assumed to be higher for females than for males (Espírito-Santo et al 2003). In F. mandshurica, flowers appear before the leaves in April and the fruits are visible after litter fall in October.…”

Population size, sex-ratio and sexual dimorphism in <em>Fuchsia parviflora</em> (Onagraceae) an endemic dioecious shrub

“…Hypotheses that try to explain male-biased sex ratios on dioecious species, emphasize the divergent allocation to vegetative and reproductive process in males and female plants (Lloyd & Webb 1977, Johnson et al 2015. Accordingly, a higher reproductive allocation by females (because they need to allocate nutrients to flowers, fruits and seeds, whereas males invest only in flowers) may reduce their vegetative growth, flowering frequency and increase mortality among female plants, increasing male-biased sex ratios (Lloyd & Webb 1977, Espírito-Santo et al 2003. However, few empirical studies have actually measured total investment in reproduction of males and females (see Avila-Sakar & Romanow 2012, Johnson et al 2015.…”