Fragment size, pollination efficiency and reproductive success in natural populations of wind-pollinated Polylepis australis (Rosaceae) trees

It is well known that habitat fragmentation is likely to negatively affect the reproductive success of a species. Despite this fact, studies on the effects of fragmentation on reproductive success in combination with effects on natural pollination of wind-pollinated tree species are very rare. In this study, we analyzed the relationships between fragment size, components of pollination efficiency, reproductive success and progeny vigour of the highly fragmented populations of the wind-pollinated treeline species Polylepis australis (Rosaceae) in Argentina. We conducted our study in the high mountains of Córdoba, comparing pollination efficiency and reproduction between four fragment sizes. Most of our results indicate that P. australis is currently insensitive to fragmentation. However, our study revealed also a linear increase in leaf area and biomass of 40-day-old seedlings with increasing fragment size. Inbreeding problems through fragmentation as well as decreased habitat quality in small fragments are discussed as possible causes for the impaired progeny vigour.     

Thread-forming structures in angiosperm anthers: Their diverse role in pollination ecology

This paper reviews the origin, nature, systematic distribution, and the respective function of the highly variable and diverse thread-forming structures in angiosperm anthers (including somewhat similar, rare features in ferns and gymnosperms). On one hand, such threads may function as pollen-connecting vectors in forming pollen dispersal units, as sporopollenin threads (viscin threads), e.g. in Onagraceae, or sporopollenin-less threads in surprisingly many other angiosperm families. On the other hand, as is known from theImpatiens — pollen basket, threads or ropes may be involved in pollen presentation. In addition, for the first time two new examples of pollen baskets in Boraginaceae and Scrophulariaceae are reported. InEchium the basket is formed by cellular elements from the modified septal regions, whereas inEsterhazya a similar effect is achieved in an analogous manner by trichomes of the epidermal layer of the thecal wall. There is obviously a different function of these seemingly very similar baskets: inEchium the feature acts preferably as a pollen presentation agent, whereas inEsterhazya the primary function is to prevent all the pollen from being dispersed too soon.     

Population size, pollination and reproductive success in two endangered Genista species

Habitat fragmentation often leads to small and isolated plant populations as well as decreased habitat quality. These processes can fundamentally disrupt the interactions between plants and pollinators and decrease reproductive success. This concerns especially self-incompatible, non-clonal species that depend on pollination for successful reproduction.In two rare and endangered heathland plant species, Genista anglica and G. pilosa, we examined pollination and reproduction in relation to population size. Eight populations of G. anglica and ten populations of G. pilosa were surveyed in the vicinity of Bremen, NW-Germany. We counted the visits of pollinators (honeybees, bumblebees, and other insects) and determined the reproductive output of the observed shoots.Contrary to our expectation to find increased pollinator visitation rates in larger populations of both Genista species, the number of flower-visiting insects was unrelated to the number of flowering shoots. Increasing shoot length had a positive and increasing temperature a negative impact on the number of visiting honeybees and bumblebees. Despite the general absence of population size effects on pollinator numbers, the number of fruits and seeds in G. anglica increased with increasing population size. Fruit and seed set in G. pilosa were negatively related to the number of ‘other insects’. Our field observations showed that larger populations of both Genista species flowered earlier than smaller populations and much earlier than reported in the literature. Flowering in large populations therefore tends to coincide less well with pollinator abundance, and this may cause a disruption of the temporal coincidence between flowering phenology and pollinator activity.     

Pollen wall stratification and pollination

Qualities of the stratified pollen walls were evaluated for their possible role in pollination (pollination modes, and pollen tube formation). The importance of studying pollen grains in their respective natural state is noted. Examples of pollen morphological features specific to pollination vectors are rare and difficult to demonstrate. However, some complex, but significant correlations are reported.     

In vitro pollination of angiosperm ovules with gymnosperm pollen grains

Summary Pollen grains of the gymnosperm species Ephedra distachya and Pinus wallichiana germinated abundantly on the in vitro cultured placentae of the angiosperm species Nicotiana tabacum, Melandrium album and Allium moly. Some P. wallichiana pollen tubes entered the micropyles of M. album. Embryological observations of cross-pollinated M. album ovules 2 or 3 d after cross-pollination revealed the presence of pollen tube remnants within the embryo sacs. Karyological disturbances in the two- and three-celled proembryos and endosperm nuclei indicated their probable hybrid origin. In some crosses, gynogenetic haploid proembryos were also noticed.     

Pollinator activity and pollination success of Medicago sativa L. in a natural and a managed population

Medicago sativa L. is an important cash crop in the arid region of northwest China. Pollinator activity is an essential aspect of pollination success, but the relationships between pollinator visitation rate and seed set still need further study of M. sativa. We investigated the following characteristics of M. sativa in natural and managed populations: floral traits, pollinator activity, and breeding system. Our results indicated the management could affect the number of flowers produced; however, there was no detectable effect on the seed set per flower. We found the percentage of seeds among pollinated flowers in the managed population was significantly higher than that in the natural population. Moreover, the increase in the proportion of pollinated flowers could significantly increase seed set per flower, and pollinator visitation rate was the important limiting factor for seed set in both populations. Andrena lebedevi Popov was found to be the most frequent pollinator in both populations. Outcrossing was dominant in the breeding system and insect pollination played an important role in outcrossing. Our study suggested that proper management (artificial selection) could promote pollination success of M. sativa.     

Floral display and pollination success in Senecio jacobaea (Asteraceae): Interactive effects of head and corymb size

The self-sterile Senecio jacobaea (Asteraceae) presents its rayed heads in large, compound inflorescences (corymbs). I examined the role of head and corymb size in pollinator attraction, and whether the positive effect of intact rays (if any) depends on the size of the corymb. Using female fertility as a measure of pollination success, I assessed the performance of stems representing four experimentally produced character combinations: (1) few heads without rays, (2) many heads without rays, (3) few heads with rays, and (4) many heads with rays. The proportion of flowers setting fruit was higher for intact stems (treatments 2, 4) than for stems on which the majority of the heads had been removed (treatments 1, 3), suggesting selection for maximum inflorescence production. By contrast, experimental removal of all rays had a relatively weak negative effect on fruit set, with few-headed stems (treatment 1) experiencing a greater reduction than stems with many heads (treatment 2). These results suggest that clusters of heads produce a synergistic effect on pollinator attraction, allowing plants to maintain high visitation rates even if there are drastic reductions in the basic attraction units. Hence, the number of heads and the attractiveness of the individual heads interacted in their effect on pollination success. Fruit set per flower differed greatly between sites and was positively correlated with plant density.     

Seed set inCichorium intybus L. by pollination of flowers developedin vitro

Formation of viable seeds ofCichorium intybus L. was achieved in anin vitro system. Flower formation, pollination, fertilization, embryogenesis and seed development occurredin vitro on chicory root explants on culture medium lacking plant growth regulators. After flower induction under a 24-h daylength treatment, the explants were transferred to a 16-h daylength at 40 E m^-2s^-1 irradiance for pollination and further seed development. Negative results were obtained when root explants were maintained continuously under a 24-h daylength during the whole culture period. Lower seed set was obtained when the cultures were at low irradiance. The need of a dark period and adequate level of irradiance are suggested as important factors to obtain viable seeds. The developedin vitro system can be used as a model to study the factors controlling the reproductive processes, and for the study of self-incompatibility in chicory.     

Effects of season and population size on pollination and reproductive output in a Mediterranean shrub

• Pollinator guilds may change throughout extended flowering periods, affecting plant reproductive output, especially in seasonal climates. We hypothesised a seasonal shift in pollinator guild and an autumn reduction in pollinator abundance, especially in small and sparse populations.
• We recorded pollinator identity, abundance and behaviour in relation to flower density from plant to population throughout the extended flowering of Ononis tridentata. We evaluated female reproductive output by recording pollination success and pre‐dispersal seed predation in eight populations of contrasting size and density. Offspring quality was also characterised through seed weight and germination.
• A diverse guild of insects visited O. tridentata in spring, while only Apis mellifera was observed in autumn. Visitation frequency did not vary seasonally, but the number of flowers per foraging bout was lower, and seeds were heavier and had a higher germination rate in autumn. Plant and neighbourhood flowering display were not related to pollinator visitation frequency or behaviour. However, the rate of fertilised ovules, seed set and autumn flowering display size were positively related to population density.
• The maintenance of pollination in autumn enhances the reproductive performance of O. tridentata due to higher quality of autumn seed, and to a large reduction in seed predator pressure. We also suggest that observed changes in pollinator behaviour could be one of the processes behind seasonal variation in seed performance, since geitonogamous crosses were less likely to occur in autumn.

     

不同年际间异子蓬种子大小、萌发能力及结实格局

异子蓬(Borszczowia aralocaspica)为中亚荒漠特有种,在我国仅分布于新疆,其果实具有二型性。对同一生长地2006、2007、2008年异子蓬种子的大小、萌发特性及结实格局进行比较,结果表明:(1)年份和种子类型对种子大小和重量均有显著影响(P<0.05)。(2)2种类型种子具有不同的萌发行为,褐色种子萌发率高(>90%),萌发速度快,而黑色种子萌发率低(2006年的萌发率为31%),萌发速度慢;2种类型种子的萌发指数在不同年际间均差异显著。(3)不同年际间,种子总数、褐色种子数、黑色种子数均具有极显著差异(P<0.001),且随个体的增大黑色种子的比例逐渐减小,褐色种子的比例逐渐增大,并且黑色种子数目均高于褐色种子数目。该研究为深入认识异型种子的生态适应对策提供理论基础。     

The evolution of bat pollination: a phylogenetic perspective

Background

Most tropical and subtropical plants are biotically pollinated, and insects are the major pollinators. A small but ecologically and economically important group of plants classified in 28 orders, 67 families and about 528 species of angiosperms are pollinated by nectar-feeding bats. From a phylogenetic perspective this is a derived pollination mode involving a relatively large and energetically expensive pollinator. Here its ecological and evolutionary consequences are explored.

Scope and Conclusions

This review summarizes adaptations in bats and plants that facilitate this interaction and discusses the evolution of bat pollination from a plant phylogenetic perspective. Two families of bats contain specialized flower visitors, one in the Old World and one in the New World. Adaptation to pollination by bats has evolved independently many times from a variety of ancestral conditions, including insect-, bird- and non-volant mammal-pollination. Bat pollination predominates in very few families but is relatively common in certain angiosperm subfamilies and tribes. We propose that flower-visiting bats provide two important benefits to plants: they deposit large amounts of pollen and a variety of pollen genotypes on plant stigmas and, compared with many other pollinators, they are long-distance pollen dispersers. Bat pollination tends to occur in plants that occur in low densities and in lineages producing large flowers. In highly fragmented tropical habitats, nectar bats play an important role in maintaining the genetic continuity of plant populations and thus have considerable conservation value.     

Seed germination and seedling allogamy in Rosmarinus officinalis: the costs of inbreeding

• Self‐pollination by geitonogamy is likely in self‐compatible plants that simultaneously expose a large number of flowers to pollinators. However, progeny of these plants is often highly allogamous. Although mechanisms to increase cross‐pollination have been identified and studied, their relative importance has rarely been addressed simultaneously in plant populations.
• We used Rosmarinus officinalis to explore factors that influence the probability of self‐fertilisation due to geitonogamy or that purge its consequences, focusing on their effects on seed germination and allogamy rate. We experimentally tested the effect of geitonogamy on the proportion of filled seeds and how it influences germination rate. During two field seasons, we studied how life history and flowering traits of individuals influence seed germination and allogamy rates of their progeny in wild populations at the extremes of the altitudinal range. The traits considered were plant size, population density, duration of the flowering season, number of open flowers, flowering synchrony among individuals within populations and proportion of male‐sterile flowers.
• We found that most seeds obtained experimentally from self‐pollination were apparently healthy but empty, and that the proportion of filled seeds drove the differences in germination rate between self‐ and cross‐pollination experiments. Plants from wild populations consistently had low germination rate and high rate of allogamy, as determined with microsatellites. Germination rate related positively to the length of the flowering season, flowering synchrony and the ratio of male‐sterile flowers, whereas the rate of allogamous seedlings was positively related only to the ratio of male‐sterile flowers.
• Rosemary plants purge most of the inbreeding caused by its pollination system by aborting the seeds. This study showed that the rates of seed germination and allogamy of the seedlings depend on a complex combination of factors that vary in space and time. Male sterility of flowers, length of the flowering season and flowering synchrony of individuals within populations all favour high rates of cross‐pollination, therefore increasing germination and allogamy rates. Flowering traits appear to be highly plastic and respond to local and seasonal conditions.

     

Variation in predation costs with Chiastocheta egg number on Trollius europaeus: how many seeds to pay for pollination?

1. In obligate plant/seed parasite–pollinator mutualisms, the plant is exclusively pollinated by an insect whose larvae are specific seed predators. Hence, outcomes of the interaction for the plant can vary with the number of eggs laid and the number of seeds eaten per larva. 2. In the work reported here, predation by Chiastocheta larvae on seeds of Trollius europaeus was analysed as a function of the number of eggs laid on the flower. Flowers with an increasing number of eggs were bagged in three populations and seeds were counted after the end of larval predation, in order to assess whether there was competition among larvae. 3. Seed predation on single‐egg flowers was high and variable (mean per population ranging from 15 to 40% of the developed seeds). Seed predation increased weakly with increasing egg load and was lower than gross seed production (always < 85%) whatever the number of eggs laid. This corresponds to a strong decrease in seed consumption per larva with increasing egg load, i.e. severe larval competition for resources. 4. The results suggest that both interference among Chiastocheta larvae and carpel dehiscence may protect T. europaeus seeds from total predation. Estimates of seed predation based on egg load observed in 20 natural populations in the French Alps typically ranged from 30 to 60%. The interaction was always beneficial for the plant and there was no risk of total seed destruction by Chiastocheta larvae, favouring stability of the mutualism.     

濒危植物夏蜡梅(Sinocalycanthus chinensis)的开花物候与传粉成功

野外定点观测了夏蜡梅在3个群体的开花物候进程,分别计算了结实率和结籽率,并分析了始花日和开花同步性等开花物候指数对其传粉成功的影响,还进一步从个体水平分析了开花时间对传粉成功的影响.结果如下:夏蜡梅的花期在5月上旬到6月下旬,开花物候参数在不同群体间存在较明显的差异,而各群体的开花进程均呈明显的"单峰型",且开花同步性高,为"大量开花模式".群体内各开花物候参数与传粉成功相关性不明显;群体间开花物候参数中的始花日和开花中值日与结实率呈极显著的负相关,终花日与结实率和结籽率分别呈极显著和显著的负相关.个体水平不同开花时间对结实率有着显著影响(F=15.960,df=3,P＜0.01),而对结籽率影响不大(F=2.358,df=3,P=0.073).相同海拔高度小生境不同对夏蜡梅的传粉成功影响不大,但不同海拔高度对夏蜡梅的传粉成功影响显著.作为一种濒危物种,夏蜡梅这种"集中开花模式"可以吸引更多的传粉昆虫,有助于其获得更多的传粉成功,但增加了其花粉在个体内及邻近个体间的传递,不利于花粉在群体间的扩散,而导致了一定程度的自交和近交衰退,这可能是夏蜡梅群体遗传变异性低、遗传分化明显及濒危的一个原因.     

Types of pollination and seed dispersal in Mediterranean plants

Abstract

Selected examples of pollen and seed dispersal in Mediterranean plants are described. The aspects of pollination considered are: comparison between cleistogamous and chasmogamous forms in the same species; differences in attractants and rewards; duration of pollen viability according to pollination syndrome. The aspects of seed dispersal considered are: presence or absence of specialized structures for dispersal; examples of active, passive and induced dispersal; animals involved in seed dispersal and their reward; type and functions of elaiosomes.     

Cycad cone and angiosperm floral volatiles: Inferences for the evolution of insect pollination

The chemistry of the volatile emissions of male cones of four putatively insect-pollinated cycad (Cycadales) species and cones of both sexes of one wind-pollinated cycad species was analysed using GC-MS Zamia furfuracea, Macrozamia moorei, and Encephalartos altensteinii had blends consisting primarily of monoterpenoids, benzenoids, and in two causes, a di-unsaturated aliphatic hydrocarbon, while that of Zamia pumila was dominated by methyl salicylate, with sesquiterpenes and aliphatic hydrocarbons also present. In contrast, the wind-pollinated Cycas rumphii contained a series of highly alcohols, ketones and esters. The compounds classes found in the cycads are potent herbivore deterrents, and there is no apparent difference in this regard between insect- and wind-pollinated species. The results suggest convergent evolution in the gymnospermous cycads and magnoliid angiosperms of the olfactory cues that attract pollinating insects; the data are consistent with the hypothesis that early chemical attractants for pollinators evolved from herbivore deterrents.     

Transference of function in the pollination system of theOchnaceae

Most members of theOchnaceae possess poricidal anthers that are emptied by pollen collecting bees performing vibrational foraging. In several genera, such asTyleria, Adenarake, and various species ofSauvagesia, however, pollen is released by vibration from the anthers through the porus of a novel structure formed by staminodia. These envelop the androecium and gynoecium. Anthers enclosed in this envelope are often longicidal.     

Spatio-temporal variation in pollen limitation and reproductive success of two scape morphs in Primula farinosa

In plant populations where reproductive output is limited by pollinator visitation, plants with attractive floral displays should have a selective advantage. We examined the effect of inflorescence height on pollination success in Primula farinosa, which is dimorphic for scape length. To test the hypothesis that fruit and seed initiation are more strongly pollen-limited in the short-scaped than in the long-scaped morph, and that this difference is affected by spatio-temporal variation in pollen limitation, we conducted a hand-pollination experiment in four populations over 2 yr. Pollen limitation of fruit initiation varied among populations and years, and was stronger in the short-scaped than in the long-scaped morph. The results suggest that interactions with pollinators will need to be considered for a full understanding of the maintenance of this striking polymorphism. The study also shows that, although pollen limitation is likely to vary in space and time in many plant species, such variation is not necessarily associated with variation in selection on floral characters.     

Community studies in pollination ecology in the high temperate Andes of central Chile II. effect of temperature on visitation rates and pollination possibilities

Visitation rates and mean numbers of visits per flower per day are determined at three altitudinal levels (2 200–3 600 m) in the high Andes of central Chile from quantified observations of flowers visitors to a total of 134 species of plants, studied over three flowering seasons. Significant altitudinal decreases in the mean no. visits/flower/minute and per day were recorded, with Level III flowers, on the average, being pollinated only about 1/2 as frequently and to as low as 1/4 as frequently in certain months, as Level I flowers. Visitation rates are generally highest in early and mid-summer at all altitudes. — The lower visitation rates at the higher elevations are due to lower insect abundance relative to plant resources and lower levels of activity for the insects present, stemming from the generally lower ambient temperatures. Seasonal differences in visitation rates may also be related to differences in insect abundance levels. The total probability of ovule pollination cannot be estimated directly from the pollination rates, because stigmas are probably receptive for longer periods at the higher elevations. When differences in the duration of stigma receptivity are estimated from differences in flower lifelength, the probability of pollination in Level III is not very different from that expected in Level I. However, for some months, the deficit in Level III may still be substantial. — These results underline the inherent dangers of predicting pollination possibilities directly from pollination rates. They also suggest that the impoverished pollination conditions assumed in hypotheses predicting higher amounts of self-compatibility at high altitudes might not be justified for all high temperate mountains.First part of this series:Arroyo & al. (1982).