Intraspecific variation in sex allocation in hermaphroditic Plantago coronopus (L.)

Models for sex allocation assume that increased expenditure of resources on male function decreases the resources available for female function. Under some circumstances, a negative genetic correlation between investment in stamens and investment in ovules or seeds is expected. Moreover, if fitness returns for investment in male and female function are different with respect to size, sex allocation theory predicts size‐specific gender changes. We studied sex allocation and genetic variation for investment in stamens, ovules and seeds at both the flower and the plant level in a Dutch population of the wind‐pollinated and predominantly outcrossing Plantago coronopus. Data on biomass of floral structures, stamens, ovules, seedset and seedweight were used to calculate the average proportion of reproductive allocation invested in male function. Genetic variation and (genetic) correlations were estimated from the greenhouse‐grown progeny of maternal families, raised at two nutrient levels. The proportion of reproductive biomass invested in male function was high at flowering (0.86 at both nutrient levels) and much lower at fruiting (0.30 and 0.40 for the high and low nutrient treatment, respectively). Androecium and gynoecium mass exhibited moderately high levels of genetic variance, with broad‐sense heritabilities varying from 0.35 to 0.56. For seedweight no genetic variation was detected. Significant among‐family variation was also detected for the proportion of resources invested in male function at flowering, but not at fruiting. Phenotypic and broad‐sense genetic correlations between androecium and gynoecium mass were positive. Even after adjusting for plant size, as a measure of resource acquisition, maternal families that invested more biomass in the androecium also invested more in the gynoecium. This is consistent with the hypothesis that genetic variation for resource acquisition may in part be responsible for the overall lack of a negative correlation between male and female function. Larger plants had a more female‐biased allocation pattern, brought about by an increase in seedset and seedweight, whereas stamen biomass did not differ between small and large plants. These results are discussed in relation to size‐dependent sex allocation theory (SDS). Our results indicate that the studied population harboured substantial genetic variation for reproductive characters.     

Size-dependent sex allocation in hermaphroditic plants: the effects of resource pool and self-incompatibility

The effects of the resource pool and resource obtained during a season for seed maturation and self-incompatibility on the size-dependency of evolutionarily stable sex allocation were analysed theoretically. In hermaphroditic plants, reproductive resources allocated between male and female function may not be paid from a single resource pool, because plants can mature seeds using not only reserved resources but also newly gained resources after flowering. But the resource investment to male function is limited to the flowering stage. Under the assumption of constant reserve efficiency and diminishing resource return per investment to leaves, large plants should use both reserved and newly gained resources for seed maturation, while small plants should use only new resources. When both reserved and new resources are used, the optimal allocation for self-compatible species is to invest a constant amount of resources into male function irrespective of resource size, because the female fitness curve increases linearly and the male curve decelerates due to local mate competition. In self-incompatible species, on the other hand, fitness gain per investment through male function and the optimal amount of resources invested in male function decrease with size. Thus a decrease in maleness with size should be emphasized more in self-incompatible species than in self-compatible one. When only new resources are used for seed growth, the female fitness curve as well as male one decelerates with investment. Consequently, the investment in both male and female functions should increase with size, in both self-compatible and self-incompatible species. The magnitude of reserve efficiency relative to efficiency of resource gain after flowering affects size-dependent pattern of sex allocation, while the cost of seed maturation relative to ovule production has little effect on it. The plant size variation in a population emphasizes size-dependency of sex allocation. When size variation is large enough, it is possible that large plants become complete female in self-incompatible species, but it is not in self-compatible species.     

Resource Allocation and the Evolution of Self-Fertilization in Plants

This article develops a simple evolutionarily stable strategy (ESS) model of resource allocation in partially selfing plants, which incorporates reproductive and sex allocation into a single framework. The analysis shows that, if female fitness gain increases linearly with resource investment, total reproductive allocation is not affected by sex allocation, defined as the fraction of reproductive resources allocated to male function. All else being equal, the ESS total reproductive allocation increases with increasing selfing rate if the fitness of selfed progeny is more than half that of outcrossed progeny, while the ESS sex allocation is always a decreasing function of the selfing rate. Self-fertilization is much more common in annual than in perennial plants, and this association has been commonly interpreted in terms of an effect of life history on mating system. The model in this article shows that self-fertilization can itself cause the evolution of the annual habit. Incorporating the effects of pollen discounting may not have any influence on total reproductive allocation if female fitness gain is a linear function of resource investment, although the evolutionarily stable sex allocation is altered. Evolution of the selfing rate is found to be independent of reproductive and sex allocation under the mass-action assumption that self- and outcross pollen are deposited simultaneously on receptive stigmas and compete for access to ovules.     

Sex allocation in a simultaneously hermaphroditic marine shrimp

Two fundamental questions dealing with simultaneous hermaphrodites are how resources are optimally allocated to the male and female function and what conditions determine shifts in optimal sex allocation with age or size. In this study, I explored multiple factors that theoretically affect fitness gain curves (that depict the relationship between sex-specific investment and fitness gains) to predict and test the overall and size-dependent sex allocation in a simultaneously hermaphroditic brooding shrimp with an early male phase. In Lysmata wurdemanni, sperm competition is absent as hermaphrodites reproducing in the female role invariably mated only once with a single other shrimp. Shrimps acting as females preferred small over large shrimps as male mating partners, male mating ability was greater for small compared to large hermaphrodites, and adolescent males were predominant in the population during the breeding season. In addition, brooding constraints were not severe and varied linearly with body size whereas the ability to acquire resources increased markedly with body size. Using sex allocation theory as a framework, the findings above permitted to infer the shape of the male and female fitness gain curves for the hermaphrodites. The absence of sperm competition and the almost unconstrained brooding capacity imply that both curves saturate, however the male curve levels off much more quickly than the female curve with increasing level of investment. In turn, the predominance of adolescent males in the population implies that the absolute gain of the female curve is greater than that of the male curve. Last, the size-dependent female preference and male mating ability of hermaphrodites determines that the absolute gain of the male curve is greater for small than for large hermaphrodites. Taking into consideration the inferred shape of the fitness gain curves, two predictions with respect to the optimal sex allocation were formulated. First, overall sex allocation should be female biased; it permits hermaphrodites to profit from the female function that provides a greater fitness return than the male function. Second, sex allocation should be size-dependent with smaller hermaphrodites allocating more than proportionally resources to male reproduction than larger ones. This size-dependent sex allocation permits hermaphrodites to profit from male mating opportunities that are the greatest at small body sizes. Size-dependent sex allocation is also expected because the male fitness gain curve decelerates more quickly than the female gain curve and experiments indicated that resources are greater for large than small hermaphrodites. These two predictions were tested when determining the sex allocation of hermaphrodites by dissecting their gonad and quantifying ovaries versus testes mass. Supporting the predictions above, hermaphrodites allocated, on average, 118 times more to the female than to the male gonad and the proportion of resources devoted to male function was higher in small than in large hermaphrodites. A trade-off between male and female allocation is assumed by theory but no negative correlation between male and female reproductive investment was observed. In L. wurdemanni, the relationship between sex-specific investment and fitness changes during ontogeny in a way that is consistent with an adjustment of sex allocation to improve size-specific reproductive success.     

Size-dependent resource allocation among vegetative propagules and male and female functions in the forest herb Laportea bulbifera

Reproductive resource investment among vegetative propagules and male and female sexual function and their size-dependence were investigated in a perennial forest herb, Laportea bulbifera . A theoretical model based on fitness gain curves predicts that optimal investments in three reproductive modes will increase with plant size if fitness returns in all three modes increase but become saturated with investment. In a field population, large plants of L. bulbifera produced both male and female inflorescences with propagules, while small plants produced only vegetative propagules. Biomass of propagules, male inflorescences, and infructescences with achenes were all positively correlated with plant size. The increase in investment with plant size was larger for propagule production than for sexual reproduction. The relationship between propagule biomass and plant size was constant irrespective of year, while the relationship between the biomass of sexual reproductive organs and plant size differed between two successive years. Annual change of individual sex expression was investigated for 25 transplanted plants. Although each plant changed its sex expression variously among male, female and bisexual from year to year, 23 out of 25 plants produced both male and female inflorescences in at least one year. The number of viable (germinated and survived) offspring from seeds was not significantly different from the number from propagules. The production cost of a propagule was higher than that of a seed. Resource allocation theory does not seem to be applicable to size-dependent resource allocation, especially the allocation between seeds and propagules in this species.     

Variation in lifetime male fitness in Ipomopsis aggregata: tests of sex allocation theory

Sex allocation theory assumes that a shift in allocation of resources to male function both increases male fitness and decreases female fitness. Moreover, the shapes of these fitness gain functions determine whether hermaphroditism or another breeding system is evolutionarily stable. In this article, I first outline information needed to measure these functions in flowering plants. I then use paternity analysis to describe the shapes of the fitness gain functions in natural populations of the hermaphroditic herb Ipomopsis aggregata. I also explore the relationships of male fitness (number of seeds sired) and female fitness (number of seeds produced) to the number of flowers produced by a plant. Plants with greater investment of biomass in the androecium, compared to the gynoecium and seeds, showed increased success at siring seeds, assumed by the models. That sex allocation trait, however, explained only 9% of the variance in estimates of male fitness. The shapes of the fitness gain functions were consistent with theoretical expectations for a hermaphroditic plant, but the model predicted a more female-biased evolutionarily stable strategy (ESS) allocation than was observed. These results lend only partial support the classical sex allocation model.     

Effects of phenological constraints on sex allocation in cosexual monocarpic plants

The effects of two phenological constraints in resource investment to reproduction – resource limitation at the flowering stage and unpredictability of resources gained after flowering – on the resource allocation between male and female functions in monocarpic plants are considered using the ESS (evolutionarily stable strategy) approach. The model predicts that the sex allocation including the seed maturation stage has a female bias, when the quantity of reproductive resources available at flowering is small compared with that which is obtained after flowering, or when the cost of seed maturation relative to ovule production is low. The fluctuation of the quantity of resources available for seed maturation favors overproduction of ovules. As a result, more resources are allocated to female function and less to male function at flowering. The ESS allocation depends on the variability of resources and the cost of seed maturation relative to ovule production. The probability that total resource allocation has a female bias becomes higher than 0.5, and it depends on the cost of seed maturation relative to ovule production rather than resource variability. On the other hand, the probability that resource allocation has a female bias decreases with resource variability if we assume that the floral sex ratio is fixed. Future studies of plant sex allocation would profit by taking account of the phenological process of reproduction such as ovule production or seed maturation.     

Increased maleness at flowering stage and femaleness at fruiting stage with size in an andromonoecious perennial, Veratrum nigrum

Theory predicts that cosexual plants should adjust their resource investment in male and female functions according to their size if female and male fitness are differentially affected by size.However,few empirical studies have been carried out at both the flowering and fruiting stages to adequately address size-dependent sex allocation in cosexual plants.In this paper,we investigated resource investment between female and male reproduction,and their size-dependence in a perennial andromonoecious herb,Veratrum nigrum L.We sampled 192 flowering plants,estimated their standardized phenotypic gender,and assessed the resource investment in male and female functions in terms of absolute dry biomass.At the flowering stage,male investment increased with plant size more rapidly than female investment,and the standardized phenotypic femaleness (ranging from 0.267 to 0.776) was negatively correlated with plant size.By contrast,female biased allocation was found at the fruiting stage,although both flower biomass and fruit biomass were positively correlated with plant size.We propose that increased maleness with plant size at the flowering stage may represent an adaptive strategy for andromonoecious plants,because male flowers promote both male and female fertility by increasing pollinator attraction without aggravating pollen discounting.     

Allocation of resources to male and female functions in hermaphrodites

The question of"how a self-fertile hermaphrodite will distribute the resources that it allocates to reproduction is studied by means of the ESS approach. Different models of the relations between allocation to male function, the male and female fertilities, and the selfing rate, yield different conclusions about how much resource should be allocated to male function. Values below a half are obtained with one model, while another can give values greater than a half. Even with no selfing, values other than a half are usually obtained; with both models studied, the values decrease with increasing selling. If the selfing rate is assumed to be independent of the fraction of resources allocated to male function, it can be shown that the ESS allocation to male function always decreases as selling increases. The types of relations that might be expected in species with different types of breeding biology, and some data on allocation to male function, are reviewed.
The implications for the fitness of male- and female-sterility mutations are discussed. It is argued that the concavity or convexity of the curve relating female fertility to male fertility is not a good guide to when hermaphroditism should exist when there is some selfing. Even with a concave relation, male-sterility mutants can have a higher fitness than hermaphrodites, if there is some selling and inbreeding depression. Also, when the selfing rate depends on allocation to male I unction, an hermaphrodite ESS does not always exist when the function is concave (as it does when there is no selfing), and such an ESS may exist when the relation is convex. The fitness of male- or female-sterility mutants may also depend on the existence of 'fixed costs'. It is shown that these do not ailed the ESS allocation of resources.     

Facultative Sex Allocation and Sex‐Specific Offspring Survival in Barrow's Goldeneyes

Sex allocation theory predicts that females should bias their reproductive investment towards the sex generating the greatest fitness returns. The fitness of male offspring is often more dependent upon maternal investment, and therefore, high‐quality mothers should invest in sons. However, the local resource competition hypothesis postulates that when offspring quality is determined by maternal quality or when nest site and maternal quality are related, high‐quality females should invest in the philopatric sex. Waterfowl – showing male‐biased size dimorphism but female‐biased philopatry – are ideal for differentiating between these alternatives. We utilized molecular sexing methods and high‐resolution maternity tests to study the occurrence and fitness consequences of facultative sex allocation in Barrow's goldeneyes (Bucephala islandica). We determined how female structural size, body condition, nest‐site safety and timing of reproduction affected sex allocation and offspring survival. We found that the overall sex ratio was unbiased, but in line with the local resource competition hypothesis, larger females produced female‐biased broods and their broods survived better than those of smaller females. This bias occurred despite male offspring being larger and tending to have lower post‐hatching survival. The species shows strong female breeding territoriality, so the benefit of inheriting maternal quality by philopatric daughters may exceed the potential mating benefit for sons of high‐quality females.     

How geitonogamous selfing affects sex allocation in hermaphrodite plants

Does the mode of self-pollination affect the evolutionarily stable allocation to male vs. female function? We distinguish the following scenarios. (1) An ‘autogamous’ species, in which selfing occurs within the flower prior to opening. The pollen used in selfing is a constant fraction of all pollen grains produced. (2) A species with ‘abiotic pollination’, in which selfing occurs when pollen dispersed in one flower lands on the stigma of a nearby flower on the same plant (geitonogamy). The selfing rate increases with male allocation but a higher selfing rate does not mean a reduced export of pollen. (3) An ‘animal-pollinated’ species with geitonogamous selfing. Here the selfing rate also increases with male allocation, but pollen export to other plants in the population is a decelerating function of the number of simultaneously open flowers. In all three models selfing selects for increased female allocation. For model 3 this contradicts the general opinion that geitonogamous selfing does not affect evolutionarily stable allocations. In all models, the parent benefits more from a female-biased allocation than any other individual in the population. In addition, in models 2 and 3, greater male allocation results in more local mate competition. In model 3 and in model 2 with low levels of inbreeding depression, hermaphroditism is evolutionarily stable. In model 2 with high inbreeding depression, the population converges to a fitness minimum for the relative allocation to male function. In this case the fitness set is bowed inwards, corresponding with accelerating fitness gain curves. If the selfing rate increases with plant size, this is a sufficient condition for size-dependent sex allocation (more allocation towards seeds in large plants) to evolve. We discuss our results in relation to size-dependent sex allocation in plants and in relation to the evolution of dioecy.     

Genetic and environmental control of temporal and size-dependent sex allocation in a wind-pollinated plant

Sex allocation in hermaphrodites can be affected by spatial and temporal variation in resources, especially in plants where size-dependent gender modification is commonplace. The evolution of sex allocation will depend on the relative importance of genetic and environmental factors governing patterns of investment in female and male function. In wind-pollinated plants, theoretical models predict a positive relation between size and male investment because of the fitness advantages associated with more effective pollen dispersal. Theory also predicts that the timing and allocation to each sex function should depend on available resources. We grew maternal half-sibling families of annual, wind-pollinated, Ambrosia artemisiifolia in sun and shade treatments to investigate these predictions. There was significant genetic variation for female and male flower production in both sun and shade treatments. Size-dependent sex allocation occurred in the direction predicted by theory, with male flower production increasing more rapidly in larger plants. The timing of sex function also varied, with significant genetic variation for dichogamy within environments and plasticity of this trait between environments. Protandry was expressed more commonly in the sun and protogyny in the shade. The occurrence of dynamic sex allocation with changing size and experimental treatment indicates the potential for adaptive responses under different ecological conditions.     

雌雄同花植物的性分配

性分配理论假定雌雄功能之间存在着trade-off,对一种性别的投入增多必然会减少对另一性别的投入。雌雄功能投入的适合度曲线的形状决定了哪种繁育系统是进化稳定的。因此,性分配理论可以解释植物繁育系统的进化,尤其被认为是雌雄异株进化的选择机制之一。目前的实验研究分别在物种间、种群间、个体间及花间四个层次上进行:自交率的程度对物种和种群的性分配都有影响;虫媒和风媒植物的性分配是个体大小依赖的;而且花序内花的性分配模式受昆虫访花行为的影响。相对于理论,性分配的实验研究明显滞后,随着分子标记技术的普及,性分配理论将会获得更大的发展。繁殖分配需要进一步与性分配理论结合,尤其在空间尺度上资源分配与繁育系统变化的研究是很有意义的。     

Sexual dimorphism,survival, and parental investment in relation to offspring sex in a precocial bird

Differential growth rate between males and females, owing to a sexual size dimorphism, has been proposed as a mechanism driving sex‐biased survival. How parents respond to this selection pressure through sex ratio manipulation and sex‐biased parental investment can have a dramatic influence on fitness. We determined how differential growth rates during early life resulting from sexual size dimorphism affected survival of young and how parents may respond in a precocial bird, the black brant Branta bernicla nigricans. We hypothesized that more rapidly growing male goslings would suffer greater mortality than females during brood rearing and that parents would respond to this by manipulating their primary sex ratio and parental investment. Male brant goslings suffered a 19.5% reduction in survival relative to female goslings and, based on simulation, we determined that a female biased population sex ratio at fledging was never overcome even though previous work demonstrated a slight male‐biased post‐fledging survival rate. Contrary to the Fisherian sex ratio adjustment hypothesis we found that individual adult female brant did not manipulate their primary sex ratio (50.39% male, n = 645), in response to the sex‐biased population level sex ratio. However, female condition at the start of the parental care period was a good predictor of their primary sex ratio. Finally, we examined how females changed their behavior in response to primary sex ratio of their broods. We hypothesized that parents would take male biased broods to areas with increased growth rates. Parents with male biased primary sex ratios took broods to areas with higher growth rates. These factors together suggest that sex‐biased growth rates during early life can dramatically affect population dynamics through sex‐biased survival and recruitment which in turn affects decisions parents make about sex allocation and sex‐biased parental investment in offspring to maximize fitness.     

多年生龙胆属植物个体大小与花期资源分配研究

于各物种花中前期对青藏高原东部高寒草甸6种多年生龙胆属植物花期的繁殖分配和性分配进行分析,结果表明:(1)多年生龙胆属植物的植株个体越大,繁殖投入越高,繁殖分配越低;(2)随着植物个体的增大,对雌性、雄性和吸引结构的投入都在增加,这可保证资源的充分利用,不会因为单一部分的增加而造成资源的浪费;(3)6种龙胆属植物中,有4种其性分配结果与性别分配(SDS)的理论预测一致,即大个体更偏向雌性器官的资源投入,但麻花艽(Gentiana atraminea)和达乌里秦艽(Gentiana dahurica)的性分配与个体大小则没有表现出负相关,可能与其本身具有的雌雄异熟———雄性先熟特点有关;(4)资源在雌雄功能间的分配没有表现出权衡关系,可能是由于植物必须在许多不同生活史性状之间进行资源分配,而不是两两之间非此即彼.     

Resource manipulation reveals flexible allocation rules to growth and reproduction in a Mediterranean evergreen oak

Aims In plants, resource allocation to growth and reproduction may depart from trade-off expectations if (i) investment in growth and reproduction relies on different resource pools, (ii) allocation to reproduction is dependent upon reaching some growth threshold or (iii) reproduction is developmentally linked to growth, both functions relying on the same resource pool. We examined the effects of enhanced resource level on patterns of resource allocation to growth and reproduction in holm oak (Quercus ilex sbsp. ballota), a Mediterranean evergreen tree.Methods In the experimental year (2003), we manipulated the amount of soil nutrients in autumn (to increase nutrient uptake during shoot elongation in the following spring) and soil water in summer (to increase water uptake during acorn growth). Indicators of growth and male and female reproduction were estimated in the pre-experimental (2002), experimental (2003) and post-experimental (2004) years.Important findings Fertilized trees produced significantly longer shoots, but the number of female flowers per shoot was not affected by treatments. The production of male catkins was also enhanced by fertilization. Irrigation did not affect the production of female flowers or abortion rates. Growth and female reproduction showed no consistent relationship in untreated trees, but resource addition elicited a growth-female reproduction trade-off in the experimental year. The sign of this significant relationship changed in the post-experimental year, indicating the existence of lagged effects of resource manipulation on acorn production. Overall, patterns of allocation to growth and reproduction varied as a function of sex, resource availability and year, a result consistent with extreme allocational plasticity in holm oak.     

Size-dependent sex allocation within flowers of the annual herb Clarkia unguiculata (Onagraceae): ontogenetic and among-plant variation

The relative allocation of resources to male and female functions may vary among flowers within and among individual plants for many reasons. Several theoretical models of sex allocation in plants predict a positive correlation between the resource status of a flower or individual and the proportion of reproductive resources allocated to female function. These models assume that, independent of resource status, a negative correlation exists between male and female investment. Focusing on the allocation of resources within flowers, we tested these theoretical predictions and this assumption using the annual Clarkia unguiculata (Onagraceae). We also sought preliminary evidence for a genetic component to these relationships. From 116 greenhouse-cultivated plants representing 30 field-collected maternal families, multiple flowers and fruits per plant were sampled for gamete production, pollen?:?ovule ratio, seed number, ovule abortion, seed biomass/fruit, mean individual seed mass, and petal area. If sex allocation changes as predicted, then (1) assuming that flowers produced early have access to more resources than those produced later, basal flowers should exhibit a higher absolute and proportional investment in female function than distal flowers and (2) plants of high resource status (large plants) should produce flowers with a higher proportional investment in female function than those of low resource status. Within plants, variation in floral traits conformed to the first prediction. Among plants and families, no significant effects of plant size (dry stem biomass) on intrafloral proportional sex allocation were observed. We detected no evidence for a negative genetic correlation between male and female investment per flower, even when controlling for plant size.     

DOES THE TRADE-OFF BETWEEN GROWTH AND REPRODUCTION SELECT FOR FEMALE-BIASED SEXUAL ALLOCATION IN COSEXUAL PLANTS?

We analyzed sexual allocation in cosexual plants while taking the trade-off between growth and reproduction into consideration and showed that this trade-off does not select for female-biased sexual allocation. There are two problems in sexual allocation: optimizing the amount of resources allocated to reproduction in a growing season and equalizing the resources allocated to the male and the female functions. If these two are possible at the same time, equal resource allocation to the male and the female functions is the evolutionarily stable strategy (ESS; given that the fitness gains through the male and the female functions are proportional to the amount of the resources allocated to these functions). Biased sexual allocation only occurs when constraints make it impossible to simultaneously optimize allocation to reproduction and allocation to male and female functions. However, even if female-biased sexual allocation occurs due to the addition of other constraints, the trade-off between growth and reproduction itself is not an important factor that selects for female-biased sexual allocation.     

Variation in floral sex allocation in Polygonatum odoratum (Liliaceae)

BACKGROUND AND AIMS: It is well known that resource allocation to male and female functions can be highly variable in hermaphroditic plants. The purpose of this study was to investigate variations in sexual investment at different levels (flower, plant and population) in Polygonatum odoratum, a plant with sequentially opening flowers. METHODS: Pollen and ovule production in base, middle and top flowers of P. odoratum flowering shoots from two natural populations were quantified. Plant measurements of phenotypic and functional gender were calculated in both populations. Total leaf number was used to investigate the relationship between gender assessments and plant size. KEY RESULTS: Pollen and ovule production varied depending on flower position, although the precise pattern differed between both studied populations; only investment in female floral function decreased markedly from base to top flowers in both populations. The frequency distribution of phenotypic gender and their relationship with plant size differed between populations. Phenotypic and functional gender were correlated in both populations. CONCLUSIONS: Sexual investment in P. odoratum has shown a marked variability within plants, among plants, and between populations, which confirms the importance of analysing sex expression in plants of this type. Differences in relative investment in male and female components (phenotypic gender) are reflected in the functional gender and it would be expected that the evolution of sexual specialization in Polygonatum odoratum would be promoted.     

Patterns of resource allocation in the dioecious alpine herb Aciphylla simplicifolia (Apiaceae)

Abstract Patterns of reproductive and vegetative biomass allocation were compared in male and female plants of the alpine herb Aciphylla simplicifolia. Male and female plants had similar vegetative biomass but differed in the pattern of resource allocation. Inflorescences of males and females were similar in weight at the time of flowering, but differed in biomass allocation to some structures within the inflorescences, particularly those associated with ovule production and pollinator attraction (number and size of flowers). At the time of fruit production, female inflorescences were 2.6 times heavier than at flowering with developing fruit six times heavier than flowers. In addition to the increase in biomass allocated to structures associated with the provisioning and dissemination of seed, support structures (main and side stalks) were also heavier. As a result of this additional investment of resources at the time of fruit production, the reproductive effort (RE) of female plants was much higher than that of males: 37% of above ground biomass compared with 21% for males. Differences in RE did not change with plant size; however, allocation to reproduction appeared to be a constant proportion of biomass over nearly all plant sizes sampled. These results show that sex‐specific resource allocation can be a complex of temporal and morphological patterns.