LIFE-HISTORY STRATEGIES AND SEX RATIOS FOR A CULTIVAR AND A WILD POPULATION OF BUCHLOE DACTYLOIDES (GRAMINEAE)

Buchloe dactyloides (Nutt.) Engelm. is a perennial, sod-forming shortgrass of the grasslands of central North America from Montana to northern Mexico. The objectives of this research were to compare a cultivar (Sharps Improved) and a wild population from the Oklahoma panhandle, both in the field and in the greenhouse over several growing seasons, in regard to life-history strategies, sex ratios, and constancy of sex expression. Sex ratios of offspring from individual burs (usually 1–5 seeds per bur) and for all surviving plants germinated from seeds in the greenhouse were markedly different for the two populations. The wild population exhibited a 1: 1 male/female ratio with no monoecious plants and complete stability in sex expression over 3 yr of study in the greenhouse. In contrast, 13% of the cultivar plants were monoecious, and its unisexual plants showed a female bias. Burs of the two populations, in flats exposed to three separated month-long periods of favorable moisture with intervening “drought” periods, showed differential germinability of seeds within burs. The cultivar had less dormancy and produced a greater number of seedlings in the first and second periods; wild burs significantly exceeded cultivar burs in the number of seedlings during the third period and in the number of burs giving rise to seedlings in all three periods. Field and greenhouse measurements of vegetative (VRE) and sexual reproductive effort (SRE) per plant indicated that SRE was minimal (ca. 2% of aboveground biomass) in relation to asexual ramet propagation by rapidly growing stolons (VRE = ca. 80%). Mean SRE and VRE were not only similar for the populations, but also for the males and females within a population, although the values for individual plants were highly variable. It is concluded that Buchloe dactyloides is largely dioecious, with at least some wild populations showing a 1: 1 male/female ratio and constancy of sex expression, and that the bur as a dispersal unit containing 1–5 seeds is particularly appropriate for the breeding system and habitat ecology of Buchloe dactyloides.     

两种集合繁殖体形态及间歇性萌发特性——以蒺藜和欧夏至草为例

集合繁殖体(synaptospermy)是荒漠植物为适应恶劣环境条件而演化出的关键性特征,其作为植物生活史特性之一,有助于了解在荒漠环境下集合繁殖体植物的适应策略。蒺藜(Tribulus terrestris)和欧夏至草(Marrubium vulgare)分别为一年生及多年生草本植物,蒺藜扩散单位由一朵花发育而成的集合繁殖体组成,欧夏至草扩散单位由多朵花发育的集合繁殖体和种子组成,以这两种植物为材料,对其集合繁殖体形态、活力、吸水及萌发特性进行初步研究。结果显示:(1)蒺藜集合繁殖体依照发育成熟先后位置在质量、附属物刺的长度、附属物占质量百分比、种子数、活力、吸水量、萌发率及萌发速率均存在显著差异;欧夏至草集合繁殖体质量及吸水量明显大于种子,而活力、萌发率及萌发速率不存在显著差异。(2)萌发位置上,蒺藜集合繁殖体仅在长刺端位置的种子萌发,属非随机萌发,而欧夏至草集合繁殖体萌发不具有规律性,属随机萌发;萌发时间上,蒺藜和欧夏至草集合繁殖体在当季下均只萌发部分种子,具间歇性萌发特性。(3)对不同生活型植物而言,其集合繁殖体附属物对种子的保护、保水、扩散及萌发行为的功能相同,但一年生草本植物的萌发行为侧重于种群繁衍,因此蒺藜集合繁殖体在当季萌发率及萌发速率较高;多年生草本植物的萌发行为侧重于种群扩散,因此欧夏至草扩散单位多样化,且萌发率及萌发速率较低。     

Effects of Dispersal Pattern and Mammalian Herbivores on Seedling Recruitment for Virola michelii (Myristicaceae) in French Guiana1

The effects of dispersal pattern (seeds in small clumps vs. seeds scattered in pairs) and distance to the nearest Carapa procera (Meliaceae; a tree that produces seeds preferred by terrestrial vertebrates) on survival of seeds and seedlings were examined for the animal–dispersed tree species Virola michelii (Myristicaceae) in a mature forest‘at Paracou, French Guiana, in 1992 and 1993. We assessed the putative role of ground–dwelling mammalian herbivores, rodents, and ungulates that filter the seed shadow, acting either as dispersers or predators and thus modifying the original pattern of seed dispersal made by frugivores. We measured the effects of simulated seed burial by rodents using marked seeds and quantified the effect of protecting seeds and seedlings from ground–dwelling vertebrates on seedling germination and survival with fence exclosures in 1992. Dispersal pattern had short–term but no long–term effects on the proportion of V. michelii seeds that survived one year later as seedlings. In the short term, within six weeks, clumped seeds survived better than scattered seeds in both years. Marked seeds that were removed from their site of dispersal were eaten; rodents only rarely buried seeds of V. michelii, and seed burial reduced seed and seedling survivorship. The combined effect of the factors year and Carapa proximity significantly affected seed survival within six weeks. Although six–week seed survival was greater in 1993 than in 1992, seedling establishment was lower in 1993 than in 1992 following a lower rainfall regime during the key period of seed germination (February). One–year seed and seedling survivorship was similar between treatments and years. Seed survival and seedling establishment in V. michelii was dependent on vertebrates in the short term and on climate in the long term. Overall, seed and seedling survivorship depended on a combination of these factors.     

Morphology and intermittent germination characteristics of synaptospermy of Tribulus terrester

 蒺藜(Tribulus terrester)果实由5个集合繁殖体构成, 是一种常见的具集合繁殖体的一年生植物。该文对不同月份成熟的蒺藜果实及果实集合繁殖体的形态、活力、吸水率、萌发率及萌发速率进行了比较观察, 初步探讨其生态学意义。主要结果如下: 1)果实各集合繁殖体间在质量、附属物质量百分比、种子数、活力、吸水率、萌发率及萌发速率方面随其发育顺序依次减小, 存在显著差异; 2)果实平均活力及萌发率随成熟时间依次升高, 而吸水率依次降低, 平均活力及萌发率与果实成熟时间正相关, 而与吸水率负相关, 成熟时间越早, 活力及萌发率越低, 吸水率越高; 3)除9月最晚成熟的集合繁殖体在最适条件下均能萌发外, 其余月份的果实各集合繁殖体只能部分萌发, 且只有位于集合繁殖体长刺端的种子能萌发, 这种在当季只萌发部分种子, 剩下的种子仍然保持在一个扩散单元中并在数周、数月或数年间不规则地间隔萌发属于间歇性萌发。上述结果表明: 不同月份成熟果实及果实不同发育顺序的集合繁殖体在形态、活力及吸水率方面存在梯度变化, 这种变化可能是造成蒺藜间歇性萌发的主要原因, 这种萌发对策可以降低同胞后代间的竞争, 使其对可变环境中的生存风险进行有效的分摊, 为物种的延续提供保障。     

Animal dispersal dynamics promoting dioecy over hermaphroditism

Because of the separation of sexual function to male and female individuals, dioecious species have fewer pollen and seed bearers and thus experience disadvantages due to increased aggregation of reproductive function. Because of this disadvantage, models predict that dioecious females must have substantially more than twice the fecundity of hermaphrodites, yet empirical data suggest that female fecundity advantages are commonly much lower. Here, we incorporate animal foraging dynamics--and the heightened dispersal of seeds that may accompany increases in fecundity of dioecious females--into a spatially explicit mathematical model. We focus on the competition for germination sites with varying seed production, seed dispersal ability, and mortality, and we find that preferential foraging on dioecious females reduces the stringent fecundity requirements of dioecy to values in accordance with empirical estimates. This finding contributes to our understanding of the correlation between dioecy and fleshy fruits and highlights the importance of mutualist dispersers to dioecious species.     

EVOLUTION OF DIOECY IN BUCHLOE DACTYLOIDES (GRAMINEAE): TESTS FOR SEX-SPECIFIC VEGETATIVE CHARACTERS,ECOLOGICAL DIFFERENCES,AND SEXUAL NICHE-PARTITIONING

Buchloe dactyloides is a perennial dioecious grass in which male and female inflorescences are so strikingly dimorphic that they were originally assigned to different genera. The objective of this paper is to present the results of tests for sex-specific vegetative characters, ecological differences, and sexual niche-partitioning, combining them with prior information on the reproductive biology of Buchloe for an evaluation of the key factors leading to the evolution of dioecy and sexual dimorphism. Field and greenhouse data were collected from Oklahoma and Kansas populations on vegetative characters, allocation to reproduction, and relative growth and competitive success along resource gradients. Except for greater susceptibility to leaf rust by males, there were no significant differences between males and females in vegetative characters, total biomass, or reproductive effort. Field studies of spatial distributions of males and females failed to show any relation to soil, topography, or soil moisture. In a 45-month greenhouse experiment starting at the seedling stage, the relative growth and competitive success of randomly paired individuals showed no evidence for differential competitive success or for niche-partitioning of males and females. The “outcrossing advantage” and subsequent sexual specialization of the female inflorescence appear to be the major factors underlying this dimorphic system.     

THE CONSEQUENCES OF DIOECY FOR SEED DISPERSAL: MODELING THE SEED-SHADOW HANDICAP

Abstract.— Recent evidence has suggested that clades of dioecious angiosperms have fewer extant species on average than those of cosexual (hermaphroditic and monoecious) relatives. Reasons for the decrease in speciation rates and/or increase in extinction rates are only beginning to be investigated. One possibility is that dioecious species suffer a competitive disadvantage with cosexuals because only half of the individuals in a dioecious population are seed bearing. When only females produce seed, offspring will be more spatially clumped and will experience more local resource competition than when every individual produces seed. We examine two spatially explicit models to determine the effect of a reduction in seed dispersers on the invasibility and persistence of dioecious populations. Even though dioecious females were allowed to produce twice as many seeds as cosexuals, our results show that a reduction in the number of seed dispersers causes a decrease in the ability of dioecious progeny to find uninhabited sites, thus reducing persistence times. These results suggest that the maintenance of dioecy in the presence of hermaphroditic competitors requires a substantial increase in relative fitness and/or a large dispersal advantage of dioecious seeds.     

The “Foliage is the Fruit” hypothesis: Buchloe dactyloides (Poaceae) and the shortgrass prairie of North America

Janzen proposed that foliage of herbaceous plants may serve as the attractant for large herbivore dispersal of seeds. Such herbivore dispersal was envisioned to select for traits enhancing ingestion and passage of viable seeds through the animal. We tested this “Foliage is the Fruit” (FF) hypothesis by collecting and collating appropriate data from Buchloe dactyloides (buffalograss), one of the two dominant grasses of the shortgrass prairie. Passage of buffalograss diaspores through cattle had a positive effect on germination and seedling growth from intact diaspores, damage other than that due to mastication (15%) was minimal, and retention time was 1–5 days. This combination of retention time and migratory herbivores during the northward expansion of shortgrass prairie should have enhanced migration of buffalograss northward to Montana from its area of origin in central Mexico, and our comparisons with its five close dioecious relatives (the “Buchloe group”) showed that buffalograss does possess a suite of distinctive FF traits. Lab analyses of foliage quality and digestibility also confirmed the high quality of its foliage. After reviewing comparable data for Bouteloua gracilis (blue grama), we conclude that buffalograss and blue grama, which dominate major portions of the largest North American steppe Province, provide strong support for the FF hypothesis.     

Leaky dioecy in <Emphasis Type="Italic">Diospyros</Emphasis> (Ebenaceae) endemic to the Island of Mauritius

Dioecy, a rather rare phenomenon in the plant kingdom seems to be more prevalent on oceanic islands. The high incidence of dioecy on these islands could result from dioecious colonists among which a small percentage show leaky dioecy, which is an ability to self-fertilise. In this study, we report the occurrence of leaky dioecy in one of the 11 extant Diospyros species endemic to Mauritius. Female flowers on the leaky dioecious plants were artificially pollinated and bagged. Populations of D. egrettarum, D. leucomelas, D. melanida, D. revaughanii, D. tessellaria were all male-biased with a ratio of at least 2:1. Leaky dioecy occurred only in one Diospyros species, D. egrettarum where hermaphrodite plants represented 2% of the populations studied. Seeds collected from them had the same germination rate (approximately 40%) as the ones obtained from strictly unisexual female plants of D. egrettarum. The fact that leaky dioecy led to the production of fertile seeds opens the possibility that a single pioneer Diospyros plant could have played a major role in the establishment of reproductively viable populations in Mauritius.     

Establishment of chasmogamous and cleistogamous seedlings of an ant-dispersed UNDERSTORY HERB,CALATHEA MICANS (Marantaceae)

This study compares the establishment success of cleistogamous (CL, obligately selfed) and chasmogamous (CH, potentially outcrossed) seeds of the neotropical understory herb, Calathea micans (Marantaceae). In this species, CH and CL seeds are morphologically identical and are both dispersed by ants. I measured dispersal distances and analyzed seedling recruitment and seedling size for ant-planted CH and CL seeds, a protocol made possible by the fact that the seed coat of C. micans can be indelibly marked and remains attached to the base of the seedling for a few months. Seeds were taken by ants from experimental depots placed in natural conditions. In a second experiment, I planted CH and CL seeds in gap and understory sites to determine the effects of seed type and light on germination percentage, date of emergence, and seed and seedling survivorship. Ant-planted CH and CL seedlings did not differ in dispersal distance. CH and CL seeds did not differ significantly in recruitment probability and seedling size in either experiment. However, for the ant-planted seedlings, CH recruitment was higher in the understory than in the gap, while CL recruitment was uniform across light environments. In conclusion, I found a difference in the establishment success of CH and CL seeds in this understory herb, only after dispersal by ants in field conditions.     

Seed Dispersal of a High Quality Fruit by Specialized Frugivores: High Quality Dispersal?1

Dispersal quality, as estimated by the cumulative effects of dispersal, germination, seed predation, and seedling survival, was examined for Beilschmiedia pendula (Lauraceae) in Monteverde, Costa Rica. I determined the pattern of dispersal by finding seeds deposited by birds, protected the seeds from seed predators with cages to assess germination and seedling survival, and examined seed predation rates with marked seeds. Seed predation, germination, and seedling survival were compared between seeds naturally dispersed by birds and seeds placed at randomly located sites. Approximately 70 percent of seeds dispersed by birds (N= 244) were deposited <10 m from crown edges of fruiting B. pendula trees, although some seeds were dispersed at least 70 m away. Larger seeds were more likely to be dispersed under or close to the parent trees, and larger seeds produced larger seedlings. Seed size was not correlated directly with seedling survival, but larger seedlings at three months were most likely to survive one year. Seed predation by mammals and insects and seedling mortality due to fungal pathogens were concentrated beneath the crowns of parent trees. Seedlings and saplings were more abundant beneath fruiting B. pendula trees, but individuals farther away were taller on average. Thus, dispersal is beneficial for B. pendula, but such benefits appear most pronounced at a small spatial scale; seeds dispersed >30 m from the crown edges actually had a lower probability of survival than those dispersed 10–20 m. Only 10 percent of B. pendula. seeds received high‐quality dispersal in terms of landing in the zone with the highest per seed probability of seedling survival 10–20 m from parental crowns.     

潮间带盐沼植物种子及实生苗漂浮起动临界剪切应力研究

盐沼是分布在海陆过渡区域,以大型草本植物为优势种的潮间带生态系统。在潮间带生态系统中,盐沼植物的种子和实生苗在潮流作用下的漂浮起动是盐沼植物自然扩散的重要前提,决定了盐沼植物能否实现有效扩散和长距离传播。然而,目前缺乏有关盐沼植物繁殖体在复杂潮滩环境下漂浮起动扩散过程的定量研究。以长江口典型盐沼先锋物种海三棱藨草(Scirpus mariqueter)为研究对象,应用U-GEMS微观侵蚀系统,测定了在不同沉积物底质条件下,海三棱藨草种子及不同萌发阶段实生苗漂浮起动时的临界剪切应力,定量分析不同萌发阶段和沉积物底质对海三棱藨草种子和实生苗漂浮起动的影响。研究结果表明：(1)不同种子萌发阶段和沉积物底质对海三棱藨草种子和实生苗漂浮起动的临界剪切应力均有极显著影响(P<0.01);(2)随着萌发阶段的进展,海三棱藨草实生苗漂浮起动所需的临界剪切应力逐渐减小,因而随潮流漂浮起动进而扩散的机会也相应增大;(3)相比于淤泥质潮滩底质,海三棱藨草种子和实生苗在粉砂质潮滩更易于漂浮起动。研究结果丰富了盐沼植物在潮间带自然扩散过程和机理的研究,也为今后长江口及其他区域开展高效、低成本、以种子为修复...     

The effects of seed size and pericarp on seedling recruitment and biomass in Cryptocarya alba (Lauraceae) under two contrasting moisture regimes

Establishment success of plants derived from large seeds has been proposed to be greater than that of those derived from smaller ones, particularly under unfavourable conditions of moisture. Therefore, the advantages conferred by large seeds in terms of seedling performance may be modulated by abiotic conditions. The effect of seed size on Cryptocarya alba seedling performance (as determined by seedling recruitment and seedling size) was evaluated under two contrasting rainfall regimes (wet and dry year regime), simulated in the laboratory. It was also determined whether the presence of a pericarp, which had been shown to reduce germination, decreases desiccation and if this counterbalances the greater recruitment of seeds without a pericarp, especially under unfavourable conditions of moisture. Large seeds had a greater probability of recruitment and their seedlings attained a greater biomass, independently of the amount of water applied. In the simulated wet year regime, seeds with a pericarp showed a greater probability of recruitment than those lacking a pericarp. However, seedlings derived from both seed types attained a similar biomass. Under the dry year regime, seeds with and without a pericarp showed similar recruitment probabilities and their seedlings had similar biomasses. These results do not support the assumption that under favourable conditions of moisture, individual differences in seed size would not matter in term of seedling performance. A possible explanation in this case, is the presence of recalcitrant seeds in C. alba, which determines a very short time period for germination following dispersal. Therefore, any attribute that increases germination (e.g., large seeds) would be advantageous, independently of the prevailing abiotic conditions.     

Patterns of molecular evolution in dioecious and non‐dioecious Silene

Dioecy (i.e. having separate sexes) is a rather rare breeding system in flowering plants. Such rareness may result from a high probability of extinction in dioecious species because of less efficient dispersal and the costs of sexual selection, which are expected to harm dioecious species' survival on the long term. These handicaps should decrease the effective population size () of dioecious species, which in turn should reduce the efficacy of selection. Moreover, sexual selection in dioecious species is expected to specifically affect some genes, which will evolve under positive selection. The relative contribution of these effects is currently unknown and we tried to disentangle them by comparing sequence evolution between dioecious and non‐dioecious species in the Silene genus (Caryophyllaceae), where dioecy has evolved at least twice. For the dioecious species in the section Melandrium, where dioecy is the oldest, we found a global reduction of purifying selection, while on some, male‐biased genes, positive selection was found. For section Otites, where dioecy evolved more recently, we found no significant differences between dioecious and non‐dioecious species. Our results are consistent with the view that dioecy is an evolutionary dead end in flowering plants, although other scenarios for explaining reduced cannot be ruled out. Our results also show that contrasting forces act on the genomes of dioecious plants, and suggest that some time is required before the genome of such plants bears the footprints of dioecy.     

Preference of an insular flying fox for seed figs enhances seed dispersal of a dioecious species

Interactions among multiple species form complex networks of interdependences and are considered primary factors in the generation and maintenance of biodiversity. Pteropodid bats are keystone species that provide important ecosystem services of pollination and seed dispersal in the tropics and subtropics. In this study, we investigated the utilization and preference of food resources by the insular frugivorous flying fox Pteropus dasymallus. We found that fig species constituted the major portion of the diet of the flying fox (94.6%). When foraging, the flying fox preferred seed figs from female trees over gall figs from male trees in functionally dioecious fig species. Germination experiments showed a significantly higher percentage of germination for fig seeds in feces than those from pellets and ripe figs (feces: 80.2%, pellets: 23.4%, ripe figs: 32.9%). Considering the active selection of seed figs and avoidance of gall figs by foraging flying foxes, we suggest that the abundance of seed figs accurately represents food availability for dioecy. This preference for seed figs or viable seeds can effectively promote the survival of pollinating wasps and might reinforce the evolution of dioecism in figs. In addition, the effects of gut passage on seed germination, in combination with the capacity of flying foxes to travel long distances, may substantially contribute to the efficiency of flying foxes as seed dispersers.     

How do sessile dioecious species cope with their males?

In terrestrial plants the segregation of male and female reproductions on different individuals results in the seed-shadow handicap: males do not disperse any seed so that the number of local patches reached by seeds is potentially reduced in dioecious populations in comparison to hermaphrodite populations. An analytical model, incorporating a lottery-based recruitment and dispersal stochasticity, was built. The spatially mediated cost of the seed-shadow handicap has been assessed considering the criterions for the invasion of a resident hermaphrodite species by a dioecious species and the reverse invasion, both species having the same demographic parameters but assuming a likely higher fecundity for dioecious females. The reciprocal invasion of a dioecious and hermaphrodite species differing only by their fecundity is never possible. The seed-shadow handicap disappears when the dispersal or survival rate is high enough. This latter point is due to dispersal stochasticity, which allows for the existence of empty patches. A low fecundity and an aggregated seed distribution increase dispersal stochasticity and increase the positive impact of a low mortality rate on the relative competitivity of dioecy and hermaphroditism. Adding a dispersal cost has a comparable effect but also requires higher dispersal rates for the dioecious invasion.     

Limited seed dispersal shapes fine-scale spatial genetic structure in a Neotropical dioecious large-seeded palm

Seed and pollen dispersal contribute to gene flow and shape the genetic patterns of plants over fine spatial scales. We inferred fine-scale spatial genetic structure (FSGS) and estimated realized dispersal distances in Phytelephas aequatorialis, a Neotropical dioecious large-seeded palm. We aimed to explore how seed and pollen dispersal shape this genetic pattern in a focal population. For this purpose, we genotyped 138 seedlings and 99 adults with 20 newly developed microsatellite markers. We tested if rodent-mediated seed dispersal has a stronger influence than insect-mediated pollen dispersal in shaping FSGS. We also tested if pollen dispersal was influenced by the density of male palms around mother palms in order to further explore this ecological process in large-seeded plants. Rodent-mediated dispersal of these large seeds occurred mostly over short distances (mean 34.76 ± 34.06 m) while pollen dispersal distances were two times higher (mean 67.91 ± 38.29 m). The spatial extent of FSGS up to 35 m and the fact that seed dispersal did not increase the distance at which male alleles disperse suggest that spatially limited seed dispersal is the main factor shaping FSGS and contributes only marginally to gene flow within the population. Pollen dispersal distances depended on the density of male palms, decreasing when individuals show a clumped distribution and increasing when they are scattered. Our results show that limited seed dispersal mediated by rodents shapes FSGS in P. aequatorialis, while more extensive pollen dispersal accounts for a larger contribution to gene flow and may maintain high genetic diversity. Abstract in Spanish is available with online material.     

ECOLOGICAL CORRELATES OF REPRODUCTIVE TRAITS OF MEXICAN RAIN FOREST TREES

Sexual systems of 139 tree species from a tropical rain forest at Los Tuxtlas, Mexico were investigated to: 1) estimate the relative proportions of hermaphroditic, monoecious, and dioecious species; 2) describe flowers, fruits, and seeds in terms of size and weight; 3) describe flowering and fruiting phenology; and 4) correlate sexuality to pollination and dispersal syndromes, and the successional status occupied in the forest. Hermaphroditism occurred in 63% of the species, monoecism in 9%, and dioecy in 27%. Nondioecious species had larger flowers, but dioecious species had more seeds per fruit. The dioecious condition was associated with small flowers pollinated with unspecialized insects and fleshy fruits dispersed by animals at both species and generic levels. Reproductive traits were more correlated among nondioecious species than dioecious species. Pioneer species had more seeds per fruit, and longer flowering and fruiting periods, but persistent species produced heavier seeds and fruits. Flower and fruit morphological traits, sexual systems, and tree guilds are related in a comprehensive way, and a flow model based on data from this study is presented.     

Spatial seed and pollen games: dispersal,sex allocation,and the evolution of dioecy

The evolutionary forces shaping within‐ and across‐species variation in the investment in male and female sex function are still incompletely understood. Despite earlier suggestions that in plants the evolution or cosexuality vs. dioecy, as well as sex allocation among cosexuals, is affected by seed and pollen dispersal, no formal model has explicitly used dispersal distances to address this problem. Here, we present a game‐theory model as well as a simulation study that fills in this gap. Our model predicts that dioecy should evolve if seeds and pollen disperse widely and that sex allocation among cosexuals should be biased towards whichever sex function produces more widely dispersing units. Dispersal limitations stabilize cosexuality by reinforcing competition between spatially clumped dispersal units from the same source, leading to saturating fitness returns that render sexual specialization unprofitable. However, limited pollen dispersal can also increase the risk of selfing, thus potentially selecting for dioecy as an outbreeding mechanism. Finally, we refute a recent claim that cosexuals should always invest equally in both sex functions.     

Spit it out: Monkeys disperse the unorthodox and toxic seeds of Clivia miniata (Amaryllidaceae)

Seeds of many Amaryllidaceae are unorthodox (recalcitrant) and toxic, and cannot survive ingestion, yet are packaged in brightly colored fruits suggestive of zoochory. Seed dispersal and germination of the understory amaryllid, Clivia miniata, were investigated in KwaZulu‐Natal, South Africa. Motion‐activated cameras revealed that samango monkeys (Cercopithecus mitis labiatus) are the primary disperser of C. miniata seeds. They eat the mesocarp and, to a lesser extent, the exocarp, and spit the large (13 mm diameter) seeds whole and cleaned onto the forest floor. Most seeds were dispersed farther than 1 m from the parent. Experimental removal of the fruit pulp had a small positive effect on the rate of seed germination, but did not affect subsequent seedling growth rates. The main advantages of monkey dispersal of Clivia seeds appear to be short‐distance dispersal away from the dense foliage of clumped parent plants and occasional long‐distance dispersal through cheek‐pouching behavior.