RESUMEN
Gynodioecy, a state where female and hermaphrodite plants coexist in populations, has been widely proposed an intermediate stage in the evolutionary pathway from hermaphroditism to dioecy. In the gynodioecy-dioecy pathway, hermaphrodites may gain most of their fitness through male function once females invade populations. To test this prediction, comprehensive studies on sex ratio variation across populations and reproductive characteristics of hermaphrodite and female phenotypes are necessary. This study examined the variation in sex ratio, sex expression, flower and fruit production and sexual dimorphism of morphological traits in a gynodioecious shrub, Daphne jezoensis, over multiple populations and years. Population sex ratio (hermaphrodite:female) was close to 1:1 or slightly hermaphrodite-biased. Sex type of individual plants was largely fixed, but 15% of plants changed their sex during a 6-year census. Hermaphrodite plants produced larger flowers and invested 2.5 times more resources in flower production than female plants, but they exhibited remarkably low fruit set (proportion of flowers setting fruits). Female plants produced six times more fruits than hermaphrodite plants. Low fruiting ability of hermaphrodite plants was retained even when hand-pollination was performed. Fruit production of female plants was restricted by pollen limitation under natural conditions, irrespective of high potential fecundity, and this minimised the difference in resources allocated to reproduction between the sexes. Negative effects of previous flower and fruit production on current reproduction were not apparent in both sexes. This study suggests that gynodioecy in this species is functionally close to a dioecious mating system: smaller flower production with larger fruiting ability in female plants, and larger flower production with little fruiting ability in hermaphrodite plants.
Asunto(s)
Daphne/fisiología , Organismos Hermafroditas/fisiología , Evolución Biológica , Daphne/anatomía & histología , Daphne/genética , Fertilidad , Flores/anatomía & histología , Flores/genética , Flores/fisiología , Frutas/anatomía & histología , Frutas/genética , Frutas/fisiología , Geografía , Japón , Fenotipo , Polen/anatomía & histología , Polen/genética , Polen/fisiología , Polinización , Reproducción , Semillas/anatomía & histología , Semillas/genética , Semillas/fisiología , Razón de MasculinidadRESUMEN
The flowering phenology of alpine-snowbed plants varies widely depending on the time of snowmelt. This variation may cause spatial and temporal heterogeneity in pollen dispersal, which in turn may influence genetic structure. We used spatial autocorrelation analyses to evaluate relative effect of segregation in flowering time and physical distance on fine-scale spatial genetic structure (SGS) of a snowbed herb Primula cuneifolia sampled in 10-m grids within a continuous snow patch (110 x 250 m) using nine allozyme loci. Although the individual flower lasts for
Asunto(s)
Primula/genética , Enzimas/genética , Flores , Variación Genética , Proteínas de Plantas/genética , Polen/genética , Primula/fisiologíaRESUMEN
In alpine ecosystems, microscale variation in snowmelt timing often causes different flowering phenology of the same plant species and seasonal changes in pollinator activity. We compared the variations in insect visitation, pollen dispersal, mating patterns, and sexual reproduction of Rhododendron aureum early and late in the flowering season using five microsatellites. Insects visiting the flowers were rare early in the flowering season (mid-June), when major pollinators were bumblebee queens and flies. In contrast, frequent visitations by bumblebee workers were observed late in the season (late July). Two-generation analysis of pollen pool structure demonstrated that quality of pollen-mediated gene flow was more diverse late in the season in parallel with the high pollinator activity. The effective number of pollen donors per fruit (N(ep)) increased late in the season (N(ep) = 2.2-2.7 early, 3.4-4.4 late). However, both the outcrossing rate (t(m)) and seed-set ratio per fruit were smaller late in the season (t(m) = 0.89 and 0.71, seed-set ratio = 0.52 and 0.18, early and late in the season, respectively). In addition, biparental inbreeding occurred only late in the season. We conclude that R. aureum shows contrasting patterns of pollen movement and seed production between early and late season: in early season, seed production can be high but genetically less diverse and, during late season, be reduced, possibly due to higher inbreeding and inbreeding depression, but have greater genetic diversity. Thus, more pollinator activity does not always mean more pollen movement.