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.     

滨海湿地植物种群Allee效应驱动机制研究进展

Allee效应是指生物个体适应度与种群规模或密度之间呈正向关联的现象,因与植物种群动态和种群灭绝密切相关而受到生态学家的普遍重视。阐释多重胁迫下滨海湿地植物种群响应机制,从保护生物多样性和维持生态系统稳定性层面发展系统性生态修复措施成为相关研究关注的重点。本研究分别从遗传过程、花粉扩散过程和生物互作关系不同层面,总结分析了植物种群Allee效应驱动机制的研究进展。一方面,植物因遗传过程中近交衰退、遗传变异丧失、有害突变累积等遗传结构改变造成繁殖失败而引发Allee效应;另一方面,植物花粉扩散过程和动植物互作关系影响下的花粉限制也通过影响植物种群繁殖力成为驱动Allee效应的关键因素。滨海湿地水盐梯度变异及格局破碎化影响下,植物种群遭受Allee效应的风险需引起关注,维持滨海湿地植物种群适宜分布格局和生物连通过程成为缓解Allee效应的重要手段。结合生理学与化学生态学研究手段和长时间尺度动态监测技术,有助于进一步阐释环境及生物等多重胁迫下Allee效应的非线性驱动机制。     

Floral morph composition and pollen limitation in the seed set of <Emphasis Type="Italic">Nymphoides indica</Emphasis> populations

We investigated the floral morph composition and seed set of the populations in a heterostylous aquatic plant, Nymphoides indica O. Kuntze (Menyanthaceae). The bias of floral morph ratio in the populations was negatively correlated with the seed set. In the populations with biased floral morph ratio, the pollen on the stigma of the common morphs were dominated by pollen of the same morph, resulting in reduced seed set. The addition of pollen of the opposite morph on the stigmas of the common morph resulted in an increase of fruit and seed set rates. The intermorph pollination rate and the fruit and seed set rates of Nymphoides indica were highest when two floral morphs were close in the populations. Various insect species including Lepidoptera, Diptera and Hymenoptera visited the flowers. However, geitonogamous pollination was common because of the short flying distance of the pollinators. These results indicate that the seed set of Nymphoides indica is limited by the shortage of compatible pollens and that the success of intermorph pollination is influenced by spatial distribution of the two floral morphs. As Nymphoides indica is endangered, conservation of the populations with high fecundity is proposed by us.     

Is Echeveria gibbiflora (Crassulaceae) fecundity limited by pollen availability? An experimental study

1. An experimental approach, manually pollinating all the flowers of individual plants, was used to measure the effect of pollen limitation on female fecundity of the hummingbird-pollinated perennial shrub Echeveria gibbiflora in the ecological preserve of Pedregal de San Angel around México City, México. Eleven randomly selected plants were manually over-pollinated in all their flowers and another 11 were left to be freely visited by natural pollinators.
2. Manually pollinated plants produced significantly more fruit and seeds than control plants (1·38 and 1·74 times, respectively). There was no change in average mass of fruits.
3. Considering individual fruit production per plant sampled three times in one season, decreases in fruit mass and average seeds per fruit were observed within the same reproductive season for both treatments. For the manually pollinated plants, from the start to the end of the reproductive season, seed set decreased 55·9%; while in control plants seed set decreased 33·4% in the same period. For both treatments, average fruit mass decreased 26%.
4. Vegetative growth was not significantly different between control and experimental plants but hand-pollinated plants showed a smaller reproduction probability for the following year.
5. It is concluded that female fecundity in E. gibbiflora is limited by pollen early in the reproductive season and by resources in the middle and the end of the season.     

珍稀濒危沉水植物水菜花传粉生物学研究

水菜花(Ottelia cordata)是珍稀濒危的沉水植物,现仅分布在中国海南岛北部海口至文昌一带的淡水湿地,其造型优美,极具园艺观赏价值.然而,受人类活动影响,水菜花的生境急剧退缩且更加破碎化,濒临灭绝.为探究水菜花的繁殖特征和繁殖规律,该研究分析了水菜花的花部形态、性比、花粉活性、柱头可授性、反射光谱、花粉限制与无融合生殖及其传粉者类型与行为.结果表明:(1)水菜花雌雄异株,雌、雄个体的性比约为1∶2;水菜花雌、雄花形态相似,但雌花略大于雄花.(2)水菜花花粉活性和柱头可授性在花蕾期和开放期均较高.(3)中华蜜蜂(Apis cerana)是水菜花的主要传粉者,传粉效率较高且访问雄花的频率显著高于雌花.(4)水菜花雄蕊、雌蕊间的花色距离显著高于中华蜜蜂辨别的阈值(P＜0.001).(5)在自然授粉和人工授粉下,水菜花坐果率分别为95.29％和98.42％,并且不存在无融合生殖现象.综上所述,水菜花两性模拟的欺骗性传粉并不完美,传粉者可以从视觉上区分雌花和雄花;而由于水菜花雄花数量较多,传粉者低频率的\"错访\"足以达到水菜花雌花的繁殖需求.因此,在今后开展水菜花迁地保护、人工种群恢复等保育工作时,应重视水菜花种群大小、性别比例和当地传粉者种群数量.     

Pollination function transferred: modified tepals of Albuca (Hyacinthaceae) serve as secondary stigmas

Background and Aims

The stigma, a structure which serves as a site for pollen receipt and germination, has been assumed to have evolved once, as a modification of carpels, in early angiosperms. Here it is shown that a functional stigma has evolved secondarily from modified tepals in some Albuca species (Hyacinthaceae).

Methods

Deposition of pollen on Albuca floral organs by bees was recorded. Pollen germination and fruit set was measured in flowers that had pollen deposited solely on their tepals or had their tepal tips experimentally isolated or removed after pollination.

Key Results

Leafcutter bees deposit pollen onto the papillate apices of the inner tepals of Albuca flowers. Pollen germinates in tepal-derived fluid secreted 2 or 3 d after anthesis and pollen tubes subsequently penetrate the style during flower wilting. Application of cross-pollen to the inner tepal apices of A. setosa flowers led to high fruit set. No fruits were produced in pollinated flowers in which the inner tepals were mechanically isolated or removed.

Conclusions

Pollen capture by tepals in the Albuca clade probably evolved in response to selection for floral morphology that maximizes the accuracy of pollen transfer. These findings show how pollination function can be transferred among floral organs, and shed light on how the original angiosperm stigma developed from sporophylls.     

Reproductive strategies of animal-pollinated plants on high mountains: A review of studies from the “Third Pole”

Having hundreds of big mountains, the Qinghai–Tibetan Plateau and its southern boundary, the Hengduan Mountains Region, represent one of the world's biodiversity hotspots. In the so-called “Third Pole of the earth”, diverse effects of climate change and habitat heterogeneity could have driven the evolution of plant adaptive strategies. In this review, we collected and compiled recent sources of reproductive biology in animal-pollinated plants, stressing the questions that need further attention, including pollination system, pollen limitation, self-compatibility, and sexual system. We constructed plant–pollinator interaction networks based on the case studies from this region, showing that the majority of pollinators were bees, moths, butterflies, and flies were also important, and bats and birds were rare. As the unpredictable (cold, rainy or windy) weather affects pollinator activities, sexual reproduction seemed to be pollen limited, but available studies show that the exact pattern of pollen limitation is still under debate. Self-compatibility could be either a solution, or a result from pollen limitation. Moreover, plant sexual systems can be regarded as an integrated module that counters pollen limitation. As phylogenetic relationships were constructed, diverse genera experienced rapid radiation were revealed in these mountainous areas. Further studies of evolutionary transitions in reproductive systems of congeners will unveil potential factors shaping the general pattern of adaptive strategies in animal-pollinated plants. Further studies will be beneficial in using advanced new techniques, examining phenotypic selection under common gardens, and considering chemical ecology in interactions between plants and florivores, particularly in pollen fate.     

The contribution of a pollinating seed predator to selection on Silene latifolia females

Interactions, antagonistic or mutualistic, can exert selection on plant traits. We explored the role of Hadena bicruris, a pollinating seed predator, as a selective agent on its host, the dioecious plant Silene latifolia. We exposed females from artificial-selection lines (many, small flowers (SF) vs. few, large flowers (LF)) to this moth. Infestation did not differ significantly between lines, but the odds of attacked fruits aborting were higher in SF females. We partitioned selection between that caused by moth attack and that resulting from all other factors. In both lines, selection via moth attack for fewer, smaller flowers contrasted with selection via other factors for more flowers. In LF females, selection via the two components was strongest and selection via moth attack also favoured increased fruit abortion. This suggests that the moths act as more of a selective force on flower size and number via their predating than their pollinating role.     

Floral adaptation and diversification under pollen limitation

Pollen limitation (PL) of seed production creates unique conditions for reproductive adaptation by angiosperms, in part because, unlike under ovule or resource limitation, floral interactions with pollen vectors can contribute to variation in female success. Although the ecological and conservation consequences of PL have received considerable attention in recent times, its evolutionary implications are poorly appreciated. To identify general influences of PL on reproductive adaptation compared with those under other seed-production limits and their implications for evolution in altered environments, we derive a model that incorporates pollination and post-pollination aspects of PL. Because PL always favours increased ovule fertilization, even when population dynamics are not seed limited, it should pervasively influence selection on reproductive traits. Significantly, under PL the intensity of inbreeding does not determine whether outcrossing or autonomous selfing can evolve, although it can affect which response is most likely. Because the causes of PL are multifaceted in both natural and anthropogenically altered environments, the possible outcrossing solutions are diverse and context dependent, which may contribute to the extensive variety of angiosperm reproductive characteristics. Finally, the increased adaptive options available under PL may be responsible for positive global associations between it and angiosperm diversity.     

Autonomous self‐pollination in the nectarless orchid Pogonia minor

The pollination biology of the nectarless orchid Pogonia minor was investigated in central Japan. The investigation revealed that the solitary flowers failed to attract pollinators, while high rates of fruit set were observed in the natural population. Comparable levels of fruit set were obtained in bagged, artificial self‐pollinated and artificial cross‐pollinated plants, indicating that the species is not pollinator‐limited for fruit set under natural conditions. Autonomous self‐pollination in P. minor resulted from a reduced rostellum, which allowed contact between the pollinia and the stigma. Self‐pollination is thought to be an adaptive response that provides reproductive assurance under conditions of pollinator limitation. Since pollen limitation is generally known to be frequent among deceptive orchids, strong pollen limitation is probably a driving force in the autonomous self‐pollination mechanism in the nectarless orchid P. minor.     

Among-species differences in pollen quality and quantity limitation: implications for endemics in biodiverse hotspots

Background and Aims

Insufficient pollination is a function of quantity and quality of pollen receipt, and the relative contribution of each to pollen limitation may vary with intrinsic plant traits and extrinsic ecological properties. Community-level studies are essential to evaluate variation across species in quality limitation under common ecological conditions. This study examined whether endemic species are more limited by pollen quantity or quality than non-endemic co-flowering species in three endemic-rich plant communities located in biodiversity hotspots of different continents (Andalusia, California and Yucatan).

Methods

Natural variations in pollen receipt and pollen tube formation were analysed for 20 insect-pollinated plants. Endemic and non-endemic species that co-flowered were paired in order to estimate and compare the quantity and quality components of pre-zygotic pollination success, obtained through piecewise regression analysis of the relationship between pollen grains and pollen tubes of naturally pollinated wilted flowers.

Key Results

Pollen tubes did not frequently exceed the number of ovules per flower. Only the combination of abundant and good quality pollen and a low number of ovules per flower conferred relief from pre-zygotic pollen limitation in the three stochastic pollination environments studied. Quality of pollen receipt was found to be as variable as quantity among study species. The relative pollination success of endemic and non-endemic species, and its quantity and quality components, was community dependent.

Conclusions

Assessing both quality and quantity of pollen receipt is key to determining the ovule fertilization potential of both endemic and widespread plants in biodiverse hotspot regions. Large natural variation among flowers of the same species in the two components and pollen tube formation deserves further analysis in order to estimate the environmental, phenotypic and intraindividual sources of variation that may affect how plants evolve to overcome this limitation in different communities worldwide.