苏铁类植物传粉生物学研究进展(综述)

苏铁类植物是现存最古老的种子植物,研究其传粉特点,对于研究种子植物的起源与演化、植物与动物的协同进化以及苏铁类植物的繁殖机制、濒危机制有重要意义。本文从苏铁雌雄株开花物候学、传粉媒介及传粉机制等方面,对苏铁类植物传粉生物学相关研究进行综述,并提出今后该类植物传粉生物学研究的建议：对更多苏铁属种类未知的传粉机制进行研究;更广泛地应用排除法研究苏铁类特别是苏铁属植物的传粉媒介,进一步探讨传粉昆虫与苏铁类的共生关系问题。     

Reproductive biology of the South American cycad Zamia boliviana,involving brood-site pollination

Brood-site pollination mutualisms represent extreme levels of reciprocal specialization between plants and insects. Several studies have revealed intimate associations between cycads and their insect pollinators across different continents. However, the reproductive biology of South American cycads is still poorly understood, with limited empirical data available. Here, we investigated the plant–pollinator interactions of Zamia boliviana (Cycadales, Zamiaceae), which is distributed on savanna patches in Brazil and Bolivia. Our aim was to examine reproductive biology (strobili development and their visitors) to identify potential pollinators from the perspective of dioecy and expectations of obligatory mutualism. We monitored reproductive cohorts and registered the strobiliʼs visitors. We classified the visitorsʼ activities and described the behavior of the most active and recurring ones in both reproductive structures to ascertain the potential pollinators and their relationship with the Z. boliviana. In situ experiments were used to demonstrate efficacy in seed production. Although other insects visit the strobili, only one Coleoptera (Erotylidae: Pharaxonotha) was present seasonally. Pharaxonotha cerradensis was the single species capable of transporting pollen and developing a life cycle associated with polleniferous strobili, while concomitantly visiting ovuliferous strobili. Experimental tests associated with observational evidence in the cycad indicated brood-site pollination mutualism with the Erotylidae beetle, a potential pollinator of Z. boliviana. Our investigation confirmed a new case of obligatory mutualism between cycads and P. cerradensis in the New World. Future research on Zamia from South America should address pollination systems of this genus to better understand the ecology and evolution of plant–pollinator interactions.     

Plant connectivity underlies plant‐pollinator‐exploiter distributions in Ficus petiolaris and associated pollinating and non‐pollinating fig wasps

Mutualism is ubiquitous in nature, and nursery pollination mutualisms provide a system well suited to quantifying the benefits and costs of symbiotic interactions. In nursery pollination mutualisms, pollinators reproduce within the inflorescence they pollinate, with benefits and costs being measured in the numbers of pollinator offspring and seeds produced. This type of mutualism is also typically exploited by seed‐consuming non‐pollinators that obtain resources from plants without providing pollination services. Theory predicts that the rate at which pollen‐bearing ‘foundresses’ visit a plant will strongly affect the plant's production of pollinator offspring, non‐pollinator offspring, and seeds. Spatially aggregated plants are predicted to have high rates of foundress visitation, increasing pollinator and seed production, and decreasing non‐pollinator production; very high foundress visitation may also decrease seed production indirectly through the production of pollinators. Working with a nursery mutualism comprised of the Sonoran Desert rock fig, Ficus petiolaris, and host‐specific pollinating and non‐pollinating fig wasps, we use linear models to evaluate four hypotheses linking species interactions to benefits and costs: 1) foundress density increases with host‐tree connectivity, 2) pollinator production increases with foundress density, and 3) non‐pollinator production and 4) seed production decrease with pollinator production. We also directly test how tree connectivity affects non‐pollinator production. We find strong support for our four hypotheses, and we conclude that tree connectivity is a key driver of foundress visitation, thereby strongly affecting spatial distributions in the F. petiolaris community. We also find that foundress visitation decreases at the northernmost edge of the F. petiolaris range. Finally, we find species‐specific effects of tree connectivity on non‐pollinators to be strongly correlated with previously estimated non‐pollinator dispersal abilities. We conclude that plant connectivity is highly important for predicting plant‐pollinator‐exploiter dynamics, and discuss the implications of our results for species coexistence and adaptation.     

Pollination and seed predation by moths on Silene and allied Caryophyllaceae: evaluating a model system to study the evolution of mutualisms

Nursery pollinators, and the plants they use as hosts for offspring development, function as exemplary models of coevolutionary mutualism. The two pre-eminent examples--fig wasps and yucca moths--show little variation in the interaction: the primary pollinator is an obligate mutualist. By contrast, nursery pollination of certain Caryophyllaceae, including Silene spp., by two nocturnal moth genera, Hadena and Perizoma, ranges from antagonistic to potentially mutualistic, offering an opportunity to test hypotheses about the factors that promote or discourage the evolution of mutualism. Here, we review nursery pollination and host-plant interactions in over 30 caryophyllaceous plants, based on published studies and a survey of researchers investigating pollination, seed predation, and moth morphology and behavior. We detected little direct evidence of mutualism in these moth-plant interactions, but found traits and patterns in both that are nonetheless consistent with the evolution of mutualism and merit further attention.     

Impact of plant flowering phenology on the cost/benefit balance in a nursery pollination mutualism,with honest males and cheating females

This study documents the flowering phenology and its potential consequences on a nursery pollination mutualism between a dioecious plant, in which honest male plants, but not cheating females, allow the specific pollinator to reproduce within inflorescences. Very few pollinators were found to emerge during plant anthesis, leading to a low (if any) potential benefit through pollen dispersal. This opens the question why male plants do not also cheat their pollinators. Female plants flowered late in the season, when many males had just achieved their own anthesis, which increased the efficiency of pollen transfer. Finally, some late‐flowering males reached their anthesis simultaneously with females, which open the possibility for pollinator to choose between honest males and cheating females. Nevertheless, female plants were found to produce fruits, even though fruit production was limited by pollen (and pollinator) supply, meaning that cheating was not entirely retaliated by the mutualistic partner.     

Dynamics of plant–pollinator–robber systems

Plant–pollinator–robber systems are considered, where the plants and pollinators are mutualists, the plants and nectar robbers are in a parasitic relation, and the pollinators and nectar robbers consume a common limiting resource without interfering competition. My aim is to show a mechanism by which pollination–mutualism could persist when there exist nectar robbers. Through the dynamics of a plant–pollinator–robber model, it is shown that (i) when the plants alone (i.e., without pollination–mutualism) cannot provide sufficient resources for the robbers’ survival but pollination–mutualism can persist in the plant–pollinator system, the pollination–mutualism may lead to invasion of the robbers, while the pollinators will not be driven into extinction by the robbers’ invasion. (ii) When the plants alone cannot support the robbers’ survival but persistence of pollination–mutualism in the plant–pollinator system is density-dependent, the pollinators and robbers could coexist if the robbers’ efficiency in translating the plant–robber interactions into fitness is intermediate and the initial densities of the three species are in an appropriate region. (iii) When the plants alone can support the robbers’ survival, the pollinators will not be driven into extinction by the robbers if their efficiency in translating the plant–pollinator interactions into fitness is relatively larger than that of the robbers. The analysis leads to an explanation for the persistence of pollination–mutualism in the presence of nectar robbers in real situations.     

Variable nursery pollinator importance and its effect on plant reproductive success

Nursery pollination, in which insects use as hosts the very plants they pollinate, ranges from obligate mutualism to parasitism. In the non-obligate interaction between Greya moths and the host Lithophragma sp., the relative density of nursery pollinators and copollinators, which do not use plant tissues for larval development, is a key determinant of the interaction’s outcome. Silene (Caryophyllaceae) nursery pollination by Hadena moths (Lepidoptera: Noctuidae), studied primarily in Europe, is considered antagonistic because copollinators comprise a substantial proportion of the pollinator community. However, there are few studies that ascertain the direction of the Silene–Hadena interaction by taking into account both pollinator service and seed predation. Here, we report a novel comprehensive evaluation of the direction of the interaction between North American Hadena ectypa on Silene stellata, by comparing the relative contributions of nursery and copollinators to S. stellata pollination and relate this to variation in fruit predation and reproductive success of S. stellata across multiple sites and years. Hadena ectypa pollinator importance (pollen deposited/visit/h) varied between years, resulting from variable visitation rate. Copollinator importance was higher than H. ectypa in 1 year and equivalent in another. In two of three sites, lowered H. ectypa activity was not correlated with a significant decrease in plant reproductive success, indicating a negative interaction. Although pollinator service by H. ectypa is substantial in this system, copollinators’ service is at least as great, and when the cost of fruit predation is factored in, the net effect of the interaction is parasitism of host plants.     

Generalist diurnal pollination provides greater fitness in a plant with nocturnal pollination syndrome: assessing the effects of a Silene – Hadena interaction

Nursery pollination in Caryophyllaceae species by Hadena and Perizoma moths has been extensively described in the last few decades. Evidence across multiple pairs of species shows that such pollination systems constitute relatively specialized interactions, shifting between parasitism and mutualism depending on the presence of effective co‐pollinators. In this work, we describe a new specific Silene–Hadena interaction, the Silene ciliata–Hadena consparcatoides system. Although S. ciliata presents a typical nocturnal pollination syndrome, diurnal flower visitors have also been recorded, which motivated us to evaluate the costs and benefits of this nursery moth pollination to the plant. We experimentally induced two pollination regimes at non‐overlapping day‐night periods in a natural population of S. ciliata, and compared their effects on plant reproductive success from flower to seedling stages. Flower scent composition of S. ciliata and antennal responses of H. consparcatoides to this scent were recorded to evaluate the specificity of olfactory signals in this interaction system. In accordance with its nocturnal pollination syndrome, S. ciliata emitted a greater amount of flower scent compounds during the night. Some of the predominant scent compounds, such as benzaldehyde, benzyl acetate and methyl salicylate elicited signals in the antennae of H. consparcatoides. Diurnal pollination produced more fruits per flower than nocturnal pollination, but the latter produced higher brood size resulting in similar overall fecundity. However, seeds generated from diurnal pollination were heavier and germinated better. We conclude that despite its nocturnal pollination syndrome, S. ciliata achieved similar reproductive success and higher offspring vigour under the diurnal pollinator regime. Although H. consparcatoides is specialized in S. ciliata, its shortage or absence would not jeopardize the reproductive success of its host plant. On the contrary, the seed predation exerted by this nursery pollinator shifts the interaction towards parasitism.     

High Temperatures Result in Smaller Nurseries which Lower Reproduction of Pollinators and Parasites in a Brood Site Pollination Mutualism

In a nursery pollination mutualism, we asked whether environmental factors affected reproduction of mutualistic pollinators, non-mutualistic parasites and seed production via seasonal changes in plant traits such as inflorescence size and within-tree reproductive phenology. We examined seasonal variation in reproduction in Ficus racemosa community members that utilise enclosed inflorescences called syconia as nurseries. Temperature, relative humidity and rainfall defined four seasons: winter; hot days, cold nights; summer and wet seasons. Syconium volumes were highest in winter and lowest in summer, and affected syconium contents positively across all seasons. Greater transpiration from the nurseries was possibly responsible for smaller syconia in summer. The 3–5°C increase in mean temperatures between the cooler seasons and summer reduced fig wasp reproduction and increased seed production nearly two-fold. Yet, seed and pollinator progeny production were never negatively related in any season confirming the mutualistic fig–pollinator association across seasons. Non-pollinator parasites affected seed production negatively in some seasons, but had a surprisingly positive relationship with pollinators in most seasons. While within-tree reproductive phenology did not vary across seasons, its effect on syconium inhabitants varied with season. In all seasons, within-tree reproductive asynchrony affected parasite reproduction negatively, whereas it had a positive effect on pollinator reproduction in winter and a negative effect in summer. Seasonally variable syconium volumes probably caused the differential effect of within-tree reproductive phenology on pollinator reproduction. Within-tree reproductive asynchrony itself was positively affected by intra-tree variation in syconium contents and volume, creating a unique feedback loop which varied across seasons. Therefore, nursery size affected fig wasp reproduction, seed production and within-tree reproductive phenology via the feedback cycle in this system. Climatic factors affecting plant reproductive traits cause biotic relationships between plants, mutualists and parasites to vary seasonally and must be accorded greater attention, especially in the context of climate change.     

Reproductive system and fitness of Vriesea friburgensis,a self‐sterile bromeliad species

Reproductive biology and plant fertility are directly related to many aspects of plant evolution and conservation biology. Vriesea friburgensis is an epiphytic and terrestrial bromeliad endemic to the Brazilian Atlantic rainforest. Hand‐pollination experiments were used to examine the reproductive system in a wild population of V. friburgensis. Plant fertility was assigned considering flower production, fruit and seed set, seed germination, and pollen viability. Self‐sterility observed from spontaneous selfing and manual self‐pollination treatments may be the consequence of late‐acting self‐incompatibility. Hand‐pollination results indicated no pollen limitation in the population studied. Floral biology features such as a few daily open flowers, nectar production, and sugar concentration corroborate hummingbirds as effective pollinators, although bees were also documented as pollinators. Components of fitness such as high flower, fruit, and seed production together with high seed and pollen viability indicate that this wild population is viable. From a conservation point of view, we highlight that this self‐sterile species depends on pollinator services to maintain its population fitness and viability through cross‐pollination. Currently, pollinators are not limited in this population of V. friburgensis. Conversely, the maintenance and continuous conservation of this community is essential for preserving this plant–pollinator mutualism.     

Can chemical signals,responsible for mutualistic partner encounter,promote the specific exploitation of nursery pollination mutualisms? – The case of figs and fig wasps

In nursery pollination mutualisms, where pollinators reproduce within the inflorescence they pollinate, floral scents often play a major role in advertizing host location and rewards for the pollinator. However, chemical messages emitted by the plant that are responsible for the encounter of mutualist partners can also be used by parasites of these mutualisms to locate their host. Each species of Ficus (Moraceae) is involved in an obligatory nursery pollination mutualism with usually one pollinating fig wasp (Hymenoptera: Chalcidoidea: Agaonidae). In this interaction, volatile compounds emitted by receptive figs are responsible for the attraction of their specific pollinator. However, a large and diverse community of non-pollinating chalcidoid wasps can also parasitize this mutualism. We investigated whether the chemical message emitted by figs to attract their pollinator can promote the host specificity of non-pollinating fig wasps. We analysed the volatile compounds emitted by receptive figs of three sympatric Ficus species, namely, Ficus hispida L., Ficus racemosa L., and Ficus tinctoria G. Forster, and tested the attraction of the pollinator of F. hispida ( Ceratosolen solmsi marchali Mayr), and of one species of non-pollinating fig wasp [ Philotrypesis pilosa Mayr (Hymenoptera: Chalcidoidea: Pteromalidae)] to scents emitted by receptive figs of these three Ficus species. Analysis of the volatile compounds emitted by receptive figs revealed that the three Ficus species could be clearly distinguished by their chemical composition. Behavioural bioassays performed in a Y-tube olfactometer showed that both pollinator and parasite were attracted only by the specific odour of F. hispida . These results suggest that the use by non-pollinating fig wasps of a specific chemical message produced by figs could limit host shifts by non-pollinating fig wasps.     

攀枝花苏铁传粉生物学研究

在攀枝花苏铁(Cycas panzhihuaensis L.Zhou et S.Y.Yang)自然群体中,雌雄株在数量上基本相等,但雄株的无性系产量是雌株的1.31倍,小孢子叶球的数量是大孢子叶球的2.21倍,呈现偏雄现象。小孢子叶球散粉次序是从轴基部向顶部和从小孢子叶的基部向顶部进行的,散粉高峰出现在午后,风传花粉浓度在2.55m内随着距离增加而迅速下降,而在2.55m以外维持在一个较低的水平上。在大孢子叶球内发现有两种蚂蚁和一种蜚蠊类昆虫在活动,没有发现这些昆虫对大孢子叶球的破坏,小孢子叶球则几乎没有昆虫探访。清晨在大孢子叶叶片上出现许多水样液滴,可能起着将大孢子叶叶片上沉积的花粉传递至胚珠的作用。研究表明,在攀枝花苏铁的传粉过程中,风是将花粉从小孢子叶球传至大孢子叶球的唯一媒介,大孢子叶球内活动的昆虫和大孢子叶叶片上的液滴同样起着传粉媒介作用,但不排除风传花粉一步到位的可能性。     

Pollination Biology of Cycas panzhihuaensis L. Zhou et S.Y.Yang

The population of cone-bearing cycad, Cycas panzhihuaensis L. Zhou et S. Y. Yang, was male-biased. Although the number of male individuals was almost equal to that of female individuals, the clonal and cone production of male individuals was 1.31 and 2.21 times as much as that of female individuals respectively. The sequence of pollen shedding was from the base to the top of the cone and microsporophyll. The peak of daily pollen shedding occurred at noon and in the afternoon. The airborne pollen concentration decreased quickly within 2.55 m and finally maintained at a low level along with the distance from emitting male cone. The megastrobilus was transformed into a receptive state at the beginning of pollination due to the regular morphological changes of megasporophylls. Two kinds of ants and one kind of cockroaches were found to be active within the megas- trobili during pollination, albeit causing no tissue damage. The microstrobili gave off a strong odor of fennel that could dispel all the insects nearby. The sterile foliar structure of the megasporophyll was able to secret aqueous droplets at dawn which might function as transporting adhered pollen grains by dislodging and accumulating them on or near micropyles during the process of droplets falling. Resuits from field observation showed that pollination of C. panzhihuaensis might be accomplished by different pollinators. Pollen grains were firstly wind-transported from microstrobili to megastrobili and then insects and secreted droplets on the megasporophyll either directly or indirectly carried the pollen grains to ovules within a megastrobilus. However, insects might play as a subsidiary pollinator due to the preferential concentration of airborne pollen grains transported to the megasporophylls.     

Is there a floral parasite mutualism in cycad pollination? the pollination biology of Encephalartos villosus (Zamiaceae)

Observations and experiments were carried out over 5 yr to distinguish between wind and insect pollination in the cycad Encephalartos villosus Lemaire (Zamiaceae). They were also designed to determine whether a pollination mutualism exists between E. villosus and Antliarhinus zamiae (Thunberg) (Coleoptera: Brentidae), an obligate ovule parasite that routinely parasitizes a large proportion of the ovules. The percentage of fertilized ovules dropped slightly when wind was excluded from the megastrobilus. However, when insects were excluded by either net bags or insecticide there was a substantial decrease in the proportion of fertilized ovules. Five beetle species belonging to four families were found on the strobili at the time of pollination. Using data on the effectiveness of pollen transfer to the receptive ovule, as well as data on abundance and pollen loads, a pollinator importance value (PIV) was determined for each beetle species and a pollinator importance index (PII) was determined for each population. PII values showed that an undescribed weevil (Porthetes sp., Curculionidae) was consistently the most important pollinator. A. zamiae and an undescribed beetle species within the Xenoscelinae (Languriidae) played a minor role in pollination, and their contributions varied from year to year and between populations. Two additional beetle species, Metacucujus goodei Endrödy-Younga (Boganiidae) and a second species of Xenoscelinae, had very low PII values and probably had little or no effect on pollination. Low PIV scores for A. zamiae were a result of its low numbers on the microstrobilus and the tendency of the beetles to remain on the outside of the megastrobilus. In the interaction between E. villosus and A. zamiae, the cycad does not appear to benefit significantly from a pollination service and I interpret this to mean that the relationship is antagonistic rather than mutualistic. There is, however, a possible mutualism between Porthetes sp. and E. villosus.     

Diverse pollinator communities enhance plant reproductive success

Understanding the functional consequences of biodiversity loss is a major goal of ecology. Animal-mediated pollination is an essential ecosystem function and service provided to mankind. However, little is known how pollinator diversity could affect pollination services. Using a substitutive design, we experimentally manipulated functional group (FG) and species richness of pollinator communities to investigate their consequences on the reproductive success of an obligate out-crossing model plant species, Raphanus sativus. Both fruit and seed set increased with pollinator FG richness. Furthermore, seed set increased with species richness in pollinator communities composed of a single FG. However, in multiple-FG communities, highest species richness resulted in slightly reduced pollination services compared with intermediate species richness. Our analysis indicates that the presence of social bees, which showed roughly four times higher visitation rates than solitary bees or hoverflies, was an important factor contributing to the positive pollinator diversity–pollination service relationship, in particular, for fruit set. Visitation rate at different daytimes, and less so among flower heights, varied among social bees, solitary bees and hoverflies, indicating a niche complementarity among these pollinator groups. Our study demonstrates enhanced pollination services of diverse pollinator communities at the plant population level and suggests that both the niche complementarity and the presence of specific taxa in a pollinator community drive this positive relationship.     

New frontiers in competition for pollination

Background

Co-flowering plant species frequently share pollinators. Pollinator sharing is often detrimental to one or more of these species, leading to competition for pollination. Perhaps because it offers an intriguing juxtaposition of ecological opposites – mutualism and competition – within one relatively tractable system, competition for pollination has captured the interest of ecologists for over a century.

Scope

Our intent is to contemplate exciting areas for further work on competition for pollination, rather than to exhaustively review past studies. After a brief historical summary, we present a conceptual framework that incorporates many aspects of competition for pollination, involving both the quantity and quality of pollination services, and both female and male sex functions of flowers. Using this framework, we contemplate a relatively subtle mechanism of competition involving pollen loss, and consider how competition might affect plant mating systems, overall reproductive success and multi-species interactions. We next consider how competition for pollination might be altered by several emerging consequences of a changing planet, including the spread of alien species, climate change and pollinator declines. Most of these topics represent new frontiers whose exploration has just begun.

Conclusions

Competition for pollination has served as a model for the integration of ecological and evolutionary perspectives in the study of species interactions. Its study has elucidated both obvious and more subtle mechanisms, and has documented a range of outcomes. However, the potential for this interaction to inform our understanding of both pure and applied aspects of pollination biology has only begun to be realized.Key words: Alien plants, climate change, competition for pollination, facilitation, mating system, mechanism, Lythrum, Mimulus, pollinator visitation, sexual function, invasive species, pollen loss     

Plant reproductive susceptibility to habitat fragmentation: review and synthesis through a meta-analysis

The loss and fragmentation of natural habitats by human activities are pervasive phenomena in terrestrial ecosystems across the Earth and the main driving forces behind current biodiversity loss. Animal-mediated pollination is a key process for the sexual reproduction of most extant flowering plants, and the one most consistently studied in the context of habitat fragmentation. By means of a meta-analysis we quantitatively reviewed the results from independent fragmentation studies throughout the last two decades, with the aim of testing whether pollination and reproduction of plant species may be differentially susceptible to habitat fragmentation depending on certain reproductive traits that typify the relationship with and the degree of dependence on their pollinators. We found an overall large and negative effect of fragmentation on pollination and on plant reproduction. The compatibility system of plants, which reflects the degree of dependence on pollinator mutualism, was the only reproductive trait that explained the differences among the species' effect sizes. Furthermore, a highly significant correlation between the effect sizes of fragmentation on pollination and reproductive success suggests that the most proximate cause of reproductive impairment in fragmented habitats may be pollination limitation. We discuss the conservation implications of these findings and give some suggestions for future research into this area.     

Geographical matching of volatile signals and pollinator olfactory responses in a cycad brood-site mutualism

Brood-site mutualisms represent extreme levels of reciprocal specialization between plants and insect pollinators, raising questions about whether these mutualisms are mediated by volatile signals and whether these signals and insect responses to them covary geographically in a manner expected from coevolution. Cycads are an ancient plant lineage in which almost all extant species are pollinated through brood-site mutualisms with insects. We investigated whether volatile emissions and insect olfactory responses are matched across the distribution range of the African cycad Encephalartos villosus. This cycad species is pollinated by the same beetle species across its distribution, but cone volatile emissions are dominated by alkenes in northern populations, and by monoterpenes and a pyrazine compound in southern populations. In reciprocal choice experiments, insects chose the scent of cones from the local region over that of cones from the other region. Antennae of beetles from northern populations responded mainly to alkenes, while those of beetles from southern populations responded mainly to pyrazine. In bioassay experiments, beetles were most strongly attracted to alkenes in northern populations and to the pyrazine compound in southern populations. Geographical matching of cone volatiles and pollinator olfactory preference is consistent with coevolution in this specialized mutualism.     

GEOGRAPHIC VARIATION IN REPRODUCTIVE BEHAVIOR AND SIZE STRUCTURE OF THE AUSTRALIAN CYCAD MACROZAMIA COMMUNIS (ZAMIACEAE)

Macrozamia communis is a common cycad that occurs in eastern New South Wales, Australia, where it forms an understory in various forest or woodland communities. Leaf number of reproductive individuals as well as of nonreproductive ones, taken as an indication of size class, varies clinally from north to south, with reproductive individuals in southern populations having mean leaf numbers about 12 times greater than those at the northern end of the range of this species. Female cone size and mature ovule weight appear to vary also along this gradient. Using leaf number as a predictor of sexual maturity, from 37 to 100% of the individuals present in a population were judged to be mature. The percent of mature individuals participating in the 1987 coning episode ranged from none in three southern populations to 68% elsewhere. In 9 of 10 samples more males than females participated in the 1987 coning episode, with a collective sex ratio slightly male biased for all populations sampled. In three population samples average cone numbers for male and female plants were equal. In two samples males produced more cones per plant than females. Leaf numbers of males and females in individual populations were equal. Few individuals producing cones in 1987 showed evidence of recent prior cone production, suggesting that successive cone production by both sexes is separated by an interval of several years. The periodicity with which fire is used as a fire suppression method may affect the frequency of cone production in some populations, perhaps preventing it entirely. The apparent absence of recruitment in some populations may result from long-term seed collection by humans for horticultural purposes as well as the very poor seed dispersal that appears to characterize this cycad throughout its range. The weevil Tranes internatus was observed occupying the internal tissues of female cones; this insect may be involved in the pollination of M. communis.     

高榕雌花期传粉榕小蜂和欺骗性小蜂的繁殖特点

榕树及其专一性传粉榕小蜂组成了动植物界最为经典的协同进化关系,传粉榕小蜂演化出欺骗性是非常罕见的。在雌雄同株的高榕隐头果内,共存着一种传粉榕小蜂Eupristina altissima和一种欺骗性的小蜂Eupristina sp.,两种小蜂在雌花期进入隐头果内繁殖,但有不同的繁殖特点。对比研究了两种小蜂从成虫羽化到产卵和传粉这个阶段的雌蜂个体大小、孕卵量及繁殖差异,结果表明:羽化期两种雌蜂的平均个体小,经飞行小个体的雌蜂易死亡,大个体雌蜂到达接受树,但通过苞片通道,一些个体较大的传粉榕小蜂被夹死导致进入果腔的雌蜂相对小,而欺骗性小蜂易通过苞片以至进入果腔的雌蜂个体较大。两种未产卵雌蜂均表现为个体大者孕卵量较多,但两种雌蜂的平均孕卵量没有差异。即使有充足雌花资源产卵,两种雌蜂均未产完所有卵,产卵后两种雌蜂卵巢中的卵量均显著减少,遗留下的卵量两种小蜂间没有差异。传粉榕小蜂只有部分个体传完所携带花粉,并表现为传粉越成功的雌蜂,产卵越多。存在种内竞争时,两种小蜂的产卵量均减少,传粉榕小蜂的传粉效率也降低。在种间竞争背景下,欺骗性小蜂产卵更成功,传粉榕小蜂的产卵和传粉量均受到极大抑制。研究结果说明雌花期隐头果内传粉榕小蜂只适量利用雌花资源产卵繁殖后代,更有效地传粉繁殖榕树种子,这可能是维持榕-蜂互惠系统稳定共存的重要机制之一;欺骗者稳定存在需降低与传粉者的直接竞争,而欺骗者和传粉者分散在不同果内,甚至是不同的树上繁殖是理想的繁殖策略。