Sex ratio and sexual dimorphism in the dioecious Borderea pyrenaica (Dioscoreaceae)

Abstract

Sex ratio and sexual dimorphism of Borderea pyrenaica, a long-lived dioecious geophyte endemic to the Pyrenees (north-east Iberian Peninsula), were examined in three alpine populations. In this species, age can be estimated and the sex of nonreproductive adult plants identified. Male plants attain sexual maturity earlier, flower more frequently and grow faster than female plants, whereas females allocate a higher biomass to reproduction than males. These results support the hypothesis that female plants incur a higher cost of sexual reproduction and that this higher cost is measurable as reduced vegetative growth and lower flowering frequency. Variation of sex ratio among young, intermediate and old adults within populations suggests, however, that this higher female reproductive investment does not result in sexual differences in mortality. The overall male-biased sex ratio in B. pyrenaica is mainly a consequence of the tendency of males to reproduce at an earlier age and more frequently than females.

Patterns of sexual and asexual reproduction in the brittle star Ophiactis savignyi in the Florida Keys

“…Females have been reported to have larger reproductive size thresholds in a number of non-protandrous plant (Bawa et al 1982, Lovett Doust & Lovett Doust 1988 and animal (Ayre 1984, Gillanders et al 1999) species, and these differences are frequently attributed to a greater investment in sexual reproduction by females (Darwin 1877, Garcia & Antor 1995, reviewed in Lloyd & Webb 1977. I did not, however, find evidence for differences between females and males in sexual reproductive investment in Ophiactis savignyi: females tended to have a greater mass invested in gonads at any given size relative to males, but this difference was not significant.…”

MARCADORES MORFOMÉTRICOS PARA LA IDENTIFICACIÓN DEL SEXO EN Zamia furfuracea L. f. (Zamiaceae)

“…García-Fayos (2006), because female plants store the most resources in the form of leaves and invest a small proportion of them to increase the immediate reproduction. In some biphasic species (with male and female flowers growing in sexually dimorphic branches that are spatially and temporally isolated), the storage organs of the females are larger than the males; for example, the female phase of Gurania (Cucurbitaceae) and Psiguria (Cucurbitaceae) is preceded by an increase in stem diameter (García & Antor, 1995). In this regard, the hypothesis of the advantage of size predicts that smaller individuals will express the gender that represent lower costs, in this case, male plants, whose expenditure for the production of pollen is lower than the total expenditure of metabolic energy and mineral nutrients for the production of eggs, seeds and fruits (Lovett-Doust & Lovett-Doust, 1988).…”

“…In this regard, the hypothesis of the advantage of size predicts that smaller individuals will express the gender that represent lower costs, in this case, male plants, whose expenditure for the production of pollen is lower than the total expenditure of metabolic energy and mineral nutrients for the production of eggs, seeds and fruits (Lovett-Doust & Lovett-Doust, 1988). The stem of epigaeous cycads retains a covering of dan en ramas sexualmente dimórficas y que están espacial y temporalmente aisladas), los órganos de almacenamiento de las hembras son más grandes que los de los machos; por ejemplo, la fase femenina de Gurania (Cucurbitaceae) y Psiguria (Cucurbitaceae) es precedida por un incremento en el diámetro del tallo (García & Antor, 1995). Al respecto, la hipótesis de la ventaja del tamaño predice que los individuos pequeños expresarán el género que represente menores costos; en este caso, los machos cuyo gasto para la producción de polen es menor que el gasto total de energía metabóli-ca y nutrientes minerales para la producción de los óvulos, semillas y frutos (Lovett-Doust & Lovett-Doust, 1988).…”

Biomass allocation patterns and allometric relationships between components of the androdioecious Acer tegmentosum

“…For A. tegmentosum in this study, the reproductive components of hermaphrodite trees are also green, but they do not seem to contribute much to growth. García (1995) reported that the total amount of chlorophyll in fruits accounts for almost half the biomass of the aerial part of fruiting female plants, suggesting that photosynthetic activity of green fruits is far less than that of leaves. This phenomenon is likely to vary among species and depend on their reproductive features.…”