The success of the insect sterile technique (IST) in managing insect pests raised the hypothesis that a similar approach could be employed to control weed populations. Here, we investigated the feasibility of employing irradiated sterile pollen as a means to disrupt seed production in dioecious weeds, specifically focusing on Palmer amaranth (Amaranthus palmeri S. Watson). Our goal was to determine the optimal irradiation dose that strikes a balance between inducing sterility and preserving competitiveness, as excessive doses could result in pollen mortality, while low doses may retain fertility. Plants were grown in a greenhouse during the summer of 2020 and spring of 2021. Once they reached the flowering stage, male and female individuals were isolated. Mature pollen samples were collected and exposed to varying dosages (0, 100, 200, 300, 400, and 500 Gy) of gamma rays. These irradiated and non-irradiated pollen samples were used in pollen viability assessments and hand-pollination experiments. In the hand-pollination study conducted in 2020, we employed six pollination treatments using different irradiation doses. The results showed that 300 Gy was the most effective dose, resulting in a maximum reduction of 30% in seed set compared with open pollination when irradiated pollen had prior access to the stigma through artificial pollination before open pollination. In 2021, to simulate real field conditions, three additional treatments were introduced into the study, further confirming the effectiveness of the optimal 300 Gy dose. Our findings indicate that the sterile pollen technique (SPT) using irradiated pollen can be a valuable approach for reducing weed seed production. SPT also holds potential for broad-spectrum weed control by mixing sterile pollen from multiple weed species in a single application. Additionally, it could aid in managing herbicide-resistant weeds that have survived in-season control efforts. This research contributes to the development of novel and sustainable weed management strategies.

Secondary sexual dimorphism (SSD) in flowering plants is expressed as differences in sexual characteristics that are not directly related to gamete production, involving a wide variety of morphological and physiological traits. Yerba mate (Ilex paraguariensis) is an evergreen dioecious tree native to South America. It was hypothesized that: (1) in early years, the two yerba-mate genders would segregate with lower frequency in biomass production than during later years; (2) in the case of SSD, higher biomass production would be seen for female plants when compared to male plants at a more advanced age; (3) higher SSD would appear in morphotypes that represent leaf adaptations to full sunlight cultivation; and (4) progenies originated from provenances from higher altitudes will show greater SSD in biomass production. One experiment with 135 progenies originated from six provenances with different altitudes was established in 1997 in a monoculture (under full sunlight conditions). Biomass production (leaves and thin twigs) per plant was evaluated during four harvests (1999, 2001, 2003, and 2015). The frequency of SSD in biomass production did not change throughout the plant’s life. Males were more productive than females in 1999, 2001, and 2003, while the increased frequency of more productive female plants was observed during the most recent harvest (2015), resulting in an equal frequency of female and male progenies. Sexual segregation was observed in dully green, sassafras, and gray morphotypes that are characterized by their waxy leaf structures, an adaptation to elevated irradiance and UV. As a result of adaptative responses to stressful conditions and elevated interplant variability, the relationship between SSD and biomass production of progenies originated from the highest altitudes segregated with higher frequency when compared to the lowest altitudes.

Male and female dioecious tropical trees are subjected to distinct demands that may influence their ecology. An example is Myrianthus holstii Engl. that produces persistent fruit eaten by elephants and other large mammals that frequently damage the trees. Myrianthus holstii populations were assessed with 24 2-km transects, spanning an elevation range of 1435–2495 m in the Bwindi Impenetrable National Park in Uganda. Of 1089 stems ≥ 5 cm diameter 449 were female, 383 were male and the rest were non-fertile. We also noted one apparently monoecious individual. Males produced flowers at smaller sizes than did females (minimum recorded diameters 5.5 cm and 6.8 cm, respectively). Both sexes had similar distributions, favouring moderately closed forest and mid-slope locations. Female trees were more frequently damaged and typically slightly shorter than males at large diameters. Seedling densities were positively associated with the presence of larger female trees. Our results are consistent with a life history where both sexes have similar requirements, but fruiting females experience a greater frequency of severe damage.

Fuchsia parviflora is a dioecious shrub that depends on biotic pollination for reproduction. Previous studies suggest that the male plants produce more flowers, and male-biased sex ratios have been found in some natural populations. To assess whether the biased sex ratios found between genders in natural populations are present at the point at which plants reach sexual maturity, and to identify possible trade-offs between growth and reproduction, we performed a common garden experiment. Finally, to complement the information of the common garden experiment, we estimated the reproductive biomass allocation between genders in one natural population. Sex ratios at reaching sexual maturity in F. parviflora did not differ from 0.5, except in one population, which was the smallest seedling population. We found no differences between genders in terms of the probability of germination or flowering. When flowering began, female plants were taller than males and the tallest plants of both genders required more time to reach sexual maturity. Males produced significantly more flowers than females, and the number of flowers increased with plant height in both genders. Finally, in the natural population studied, the investment in reproductive biomass was seven-fold greater in female plants than in male plants. Our results showed no evidence of possible trade-offs between growth and reproduction. Despite the fact that female plants invest more in reproductive biomass, they were taller than the males after flowering, possibly at the expense of herbivory defence.

The Cycadales are a group of significant global conservation concern and have the highest extinction risk of all seed plants. Understanding the synchronisation of reproductive phenology of Cycadales may be useful for conservation by enabling the targeting of pollen and seed collection from wild populations and identifying the window of fertilisation to aid in the cultivation of Cycadales. Phenological data for 11 species of Zamia were gathered from herbarium specimens. Four phenological characters were coded with monthly character states. DNA was isolated and sequenced for 26S, CAB, NEEDLY, matK and rbcL, and a simultaneous phylogenetic analysis of phenology and DNA sequence data was carried out. Three major clades were recovered: a Caribbean clade, a Central American clade and a South American clade. Eight species showed statistically significant synchronisation in microsporangiate and ovulate phenological phases, indicating the time of fertilisation. Close reproductive synchronisation was consistently observed throughout the Caribbean clade (statistically significant in four of five species) but was less consistent in the Central American clade (statistically significant in one of two species) and South American clade (statistically significant in three of four species). Ultimately, phenology is shown to be a potential driver of speciation in some clades of Zamia and in others to be a potential barrier to hybridisation.

In dioecious plant species different frugivore activity between genders may influence the abundance and richness of the seedling banks underneath their canopies throughout seed removal and dispersal. In the tropical dry forest of Chamela, on the Pacific Coast of Mexico, the role of S. purpurea female trees as nucleation sites of regeneration was investigated. The standing density, species richness and dispersal syndrome of woody seedlings (i.e. trees and shrubs, 10–100 cm tall) recruited underneath and outside the canopy of 10 male and 10 female S. purpurea trees were recorded in a total of 160 1-m2 plots. Total density was greater in seedling communities associated with female trees (i.e. underneath and outside their canopies) as compared with male trees (231 vs. 153 seedlings, respectively); whereas overall species richness was greater underneath female canopies. Further, the density of zoochorous species were greater underneath the canopy of S. purpurea females (range = 0–5 plants m−2), than elsewhere (outside female canopies, range = 0–3 plants m−2; underneath and outside male canopies, range = 0–2 plants m−2), suggesting a directional dispersal bias towards them. Females of dioecious plant species may act as nucleation sites of initial seedling recruitment in tropical dry forests.

Although the dioecious palm, Mauritia flexuosa plays a pivotal role in Amazonian ecology and economy, little is known about its flowering and fruiting patterns. We investigated the role of habitat and inter-annual precipitation in the phenology of M. flexuosa. We calculated sex ratios and recorded phenology for 20 mo in four populations (N = 246) of savanna–forest ecotone (two sites) and forest (two sites) habitat in Roraima, Brazilian Amazonia. Sex ratios were significantly female-biased, and >98% of females set fruit. No significant relationship was found between habitat and sex. Flowering occurred at the wet/dry season interface (August–November), and fruit maturation occurred during the wet season (May–August). Males and females flowered synchronously, and neither the onset nor termination of flowering differed significantly between habitats. Flowering was negatively associated with present precipitation and positively correlated with prior precipitation (3 mo). Fruiting was positively associated with present precipitation and unrelated to prior precipitation (3 mo). We conclude that habitat has an insignificant effect, although short-term climatic variation may influence phenology of this species in northern Amazonia. These results highlight the need for long-term studies relating flowering and fruiting events, and inter-annual climatic variation.

We investigated the pollinator assemblage in Myristica dactyloides, a dioecious tree species occupying the intermediate canopy stratum of the mid- and high-elevation wet evergreen forests and endemic to Sri Lanka and the Western Ghats of India. We surveyed two populations and, in one of them, marked four male and three female trees for observations on floral display and insect foraging, and two female trees for experimental pollination. Yellow sticky traps were used to sample insects in the canopy during the flowering season of December 2007 in addition to direct observations of insect activity in 2006. Myristicaceae members from other tropical areas have been reported to be specialized to beetle pollination, but our observations provide evidence of a generalist pollination system in M. dactyloides, composed of small, diverse insects: thysanopterans (thrips), coleopterans (beetles), halictid bees and dipterans (syrphid and phorid flies). Quantifying floral display, we found that female inflorescences were smaller, offered no reward and attracted significantly fewer pollinators in comparison to male inflorescences. Fruit set was low and could be attributed to a 29% flower abscission and abortion of young fruits, but a reasonably high natural pollination efficiency combined with pollination experiments established that there was no pollination limitation in the study population.

Dioecious plants often exhibit male-biased sex ratios and sexual differences in life history traits such as plant size, growth rate and frequency of flowering, which arise from the different costs of reproduction for male and female plants. In tropical dioecious species sexual differences in reproductive costs have been demonstrated for several subcanopy species, but few canopy dioecious trees have been studied. We recorded the sexual expression of c. 2600 trees of Cecropia schreberiana and Dacryodes excelsa, two canopy dioecious species, during several censuses over 2 y in a 16-ha plot located in ‘subtropical wet forest’ in the Luquillo Mountains, Puerto Rico. There were similar numbers of male and female trees of C. schreberiana but D. excelsa had a female-biased population. Cecropia schreberiana showed no differences in male and female diameter distributions or growth rates, suggesting that reproductive maturation and longevity are similar for both sexes. This lack of differences in size and growth rate in C. schreberiana may result from mechanisms to compensate for the higher cost of reproduction in females, no resource limitation related to its pioneer life-history, or similar male and female reproductive costs. In contrast, D. excelsa males were larger than females, probably because males grow slightly faster than females. This sexual difference in D. excelsa may reflect a higher cost of reproduction in females than in males. Spatial segregation of males and females into different habitats is not common in tropical forest and neither C. schreberiana nor D. excelsa males and females exhibited significant spatial segregation. The contrasting results for these two canopy species reflect their different life history strategies in this hurricane-affected forest.

All mature individuals of Aglaia aff. flavida (Meliaceae) were mapped in a 260 ha study area at the Crater Mountain Biological Research Station in Papua New Guinea. Sixty-four reproductively mature trees were found in an aggregated distribution with a mean inter-tree distance of 88.9 m. The sample consisted of 35 female and 29 male trees with a mean shortest distance between sexes of 232 m. Seed production and seed removal of 22 female trees was monitored throughout the 1992 fruiting season. Female trees with in 200 m of male trees generally produced large seeds crops (> 100 seeds) whereas trees farther than 200 m from the nearest male had small seed crops (< 100 seeds) regardless of female size (DBH). Most seeds (63.2%, n = 3312) produced in a sub-sample of 22 trees came from the five most fecund trees, which also produced 74.1% of the seeds that were removed by vertebrate dispersers. Where a minority of a population of rare tropical trees produce the majority of progeny, sustainable harvest practices would be most effective where highly fecund individuals are identified and conserved.

The densities of the breeding populations and the sex of all flowering individuals were recorded for five dioecious canopy tree species of Central Amazonian Myristicaceae, in 11 study areas of the Minimum Critical size of Ecosystems Project totalling 22.5 ha. Adult population densities were extremely low, ranging from 0.38 to 1.61 ha–1 for the five species studied. In a 10 ha study plot the mean distance to the nearest flowering conspecific ranged from 48 to 100 m, while the mean distance to the nearest opposite sex conspecific was 147 m. The two most abundant species, Iryanthera macrophylla and Virola calophylla, both showed male-biased sex ratios, of 23:9 and 20:6, respectively. The size class distribution of males, females and non-flowering individuals in V. calophylla suggests that earlier reproductive maturation of male plants may provide a partial explanation for this bias. In I. macrophylla, since 95% of the individuals were observed flowering, the observed ratio is representative of the population, and may be caused by sex shifts from male to female. The low reproductive densities, combined with the skewed sex ratios and overlapping generations of these species, create very small effective breeding populations, placing species such as these at great risk in the face of deforestation and habitat fragmentation.

An earlier paper (May, 1977) developed a theoretical framework for exploring the consequences of dioecy for the population dynamics of schistosomes, assuming an unbiased sex ratio. This paper extends the analysis to biased sex ratios, as have been reported in practice. We consider the relationships of the mean number and distribution of worms among hosts, the sex ratio, and the mating system (monogamous or polygamous) to: (i) the female mating probability, Φ the prevalence of mated female worms. Ω: and (iii) the mean number of mated female worms per host, ξ. Among other results, we show how high values of Φ are associated with male-biased sex ratios and polygamous mating; that Ω is independent of the mating system and is relatively unaffected by the sex ratio; and that ξ is maximal for unbiased sex ratios given monogamous mating, and for female-biased sex ratios if mating is polygamous. These results, together with the confounding effects of the mean number and distribution of worms, are described in detail in the main body of the paper.

All fig wasps are confined to figs as larvae, and their specialized diets are restricted to fig embryos, galled fig ovaries or other fig wasp larvae (Boucek 1988). Almost all of the ∼800 Ficus species (Moraceae) are involved in species-specific obligate mutualism with a pollinating fig wasp (Hymenoptera: Agaonidae), which also strictly depends on its host fig for reproduction (Berg 2003, Ramirez 1970, Wiebes 1979). More than half of all fig species are functionally dioecious, with male and female functions relegated to separate plants, called gall and seed figs (Kjellberg et al. 1987). Gall figs are functionally male because they foster the pollinator larvae that disperse the fig's pollen as adults. Seed figs are functionally female and produce only seeds. The styles are too long for pollinator ovipositors to reach the ovules, and hence they cannot lay eggs. Gall fig styles are short (Ganeshaiah et al. 1995, Weiblen et al. 1995).

Dioecious plant species differ in floral morphology and rewards between females and males. Pistillate flowers on female plants often lack pollen and can be less attractive to pollinators, which can have consequences for the visitation rates of the sexes. We studied the pollination ecology of the dioecious tree Commiphora harveyi in a coastal scarp forest in eastern South Africa. Floral display, visiting insect species, visitation rate and natural fruit set were recorded. Additionally, we pollinated flowers by hand to determine experimental fruit set. We found that male trees had more and larger flowers per inflorescence than female trees. Both sexes produced nectar in low amounts. During 203.5 h of observation we recorded 28 insect species visiting the flowers. No difference in mean visitation rate (0.20 visits per flower h−1) was recorded between the sexes. The daily and seasonal pattern was similar between the sexes. The natural fruit set was low (3.8%) and increased significantly with hand-pollination (45.5%), an indication of pollen limitation. We compared our results with the pollination ecology of C. guillauminii in Madagascar, a dioecious tree species on an island with a depauperate pollinator fauna. This comparison revealed a similar pattern with low visitation rates, low insect diversity and low fruit set, suggesting that this pattern may be more common in dioecious tree species than previously reported in the literature.

The reproductive biology of the dioecious understorey palm Chamaedorea radicalis was investigated in order to identify the primary pollen vector and quantify the relationship between female fecundity and local neighbourhood sexual composition. The study was conducted in a montane mesophyll forest within the El Cielo Biosphere Reserve, Tamaulipas, Mexico. The species is considered vulnerable in Mexico and there are concerns about the sustainability of leaf harvest. We determined that wind is the primary pollen vector, based both on floral and pollen morphological characters, and on a pollinator exclosure experiment. Successful wind pollination of this understorey palm was facilitated by the extended flowering period of males, which allows one male to be a source of pollen to receptive females for as long as a month. The number of flowers and fruits borne on a female were dependent on female size, however, no size parameter correlated well with fruit set. Fruit set was also not dependent on local sexual composition, male density or distance to the nearest male, suggesting that in this study area female reproductive success is not limited by the availability of pollen.

In dioecious plant species differences in morphology and resources between female and male flowers can have consequences for flower visitation rates. Female flowers sometimes lack pollen and can be less attractive to pollinators than male flowers. We studied the pollination ecology of the dioecious tree Commiphora guillauminii in a dry deciduous forest in western Madagascar. We recorded floral display, visiting insect species and visitation rates for female and male trees. The results showed that female trees produce significantly larger but fewer flowers per inflorescence than male ones. Number of flowers per tree did not differ between the sexes. During 270 observation-hours we observed 17 insect and two bird species visiting the flowers. Mean visitation rates of male flowers were 6.1 times higher than those of female flowers (1.07 vs. 0.18 visitors per flower h−1). Visitation rates to female and male trees showed similar daily and seasonal patterns. Fruit set (2.9%) was low, which could have been caused by pollinator or pollen limitation. This study suggests that dioecy may pose a risk for fruit set and, potentially, reproductive success for plant species with depauperate pollinator faunas on islands such as Madagascar.

Figs (Ficus species) are an important resource for a diverse array of organisms in most tropical forests (Janzen 1979 but see Gautier-Hion & Michaloud 1989). The inflorescence of Ficus, hereafter referred to as the ‘fig’, is an enclosed receptacle lined with unisexual flowers. The flowers of Ficus species are pollinated by wasps that feed on galled fig ovules as larvae and that lay eggs in fig flowers as adults (Weiblen 2002). Ripe figs are consumed by vertebrate frugivores, which are the primary dispersers of fig seeds (Shanahan et al. 2001). The interaction between figs, pollinators and frugivores introduces the potential for conflict between the roles of raising fig wasps and dispersing seeds. Specifically, the pollination mutualism could be compromised if frugivores consumed figs containing pollinator larvae. This conflict is resolved in very different ways according to the breeding system of the fig.

The pollination ecology and reproductive phenology of a dioecious palm, Chamaedorea alternans were studied at Los Tuxtlas Biological Station in Veracruz state, Mexico during the 1995-96 flowering season. The sexes flower synchronously from October to January. Field observations investigated reproductive phenology, flower visitors and inflorescence and fruit production. Males produce more flowers and inflorescences than females. Seed-set was 13%, indicating low reproductive efficiency. Individual plants showed a great variation in number of inflorescences produced. Five female and eight male plants (out of 25 and 37 plants, respectively) produced 45% of all inflorescences in the population studied. These five females also produced c. 75% of all fruits. Seed production did not show significant differences between insect-excluded and open-pollinated inflorescences, in experiments to test the efficiency of wind pollination. Flowers of this species are wind-pollinated but a great activity of undetermined species of thrips (Thysanoptera) was observed in male inflorescences.

A preliminary analysis of New Caledonian Araliaceae has shown varying degrees of support for previous hypotheses on sexual system evolution in the family. Andromonoecy, rather than hermaphroditism, is strongly supported as the ancestral sexual system for the Araliaceae. Derivation of hermaphroditism from andromonoecy in Delarbrea harmsii R. Vig. and Polyscias bracteata (R. Vig.) Lowry, ined. is also strongly supported. Support for the derivation of dioecy from andromonoecy in several New Caledonian species of Polyscias J. R. Forst. & G. Forst. depends in part on an assumption that andromonoecy cannot be secondarily derived from dioecy. The derivation of hermaphroditism from andromonoecy in Schefflera candelabra Baill. and S. pseudocandelabra R. Vig. is equivocal. The hypothesis that the immediate ancestors of Arthrophyllum Blume were andromonoecious is not supported.