蛛网萼开花物候、花部特征及繁育系统研究

为探讨蛛网萼(Platycrater arguta)传粉生物学特性,该研究以江西上饶广丰铜钹山国家级自然保护区、江西阳际峰国家级自然保护区蛛网萼为材料,采用野外观察和人工授粉等方法,对蛛网萼开花物候、花部形态及繁育系统进行了研究。结果表明:(1)蛛网萼为伞形花序,种群花期一般在6月中下旬至8月中旬,单花花期为2~3 d,花序花期持续10 d。两个保护区由于年均温度与光照的不同,花期进程有显著不同。(2)蛛网萼可孕花与不孕花从绿色变为白色时对访花昆虫有吸引作用,不孕花能够增加昆虫的访花频率。(3)蛛网萼花粉胚珠比(P/O)为2 520~3 100,杂交指数即是3或4。(4)繁育体系属于以异交为主,部分自交亲和,需要传粉者;熊蜂(Bombus sp.)、四条蜂(Apis florea)和油茶地蜂(Andrena cammelia)是蛛网萼的有效传粉昆虫。(5)套袋和人工授粉结果显示,蛛网萼为兼性自交和异交授粉,异株异花授粉能显著提高坐果率及结籽率,这主要与生境中有效传粉昆虫种类、数量少,花粉传递效率低,种群间基因流交流降低以及柱头自花及同株异花传粉等有关,从而表明在蛛网萼现有生境中植株的早期生殖成功受到影响。蛛网萼种群分布范围扩张以有性繁殖为主,无性繁殖作为重要补充及繁殖保障。     

An exception to Darwin's syndrome: floral position,protogyny, and insect visitation in Besseya bullii (Scrophulariaceae)

Darwin pointed out that plants with vertical inflorescences are likely to be outcrossed if the inflorescence is acropetalous (flowers from the bottom up), the flowers are protandrous (pollen is dispersed before stigmas are receptive), and pollinators move upward on the inflorescence. This syndrome is common in species pollinated by bees and flies, and very few exceptions are known. We investigated flowering phenology and pollinator behavior in Besseya bullii (Scrophulariaceae) and found that it did not fit Darwin's syndrome. The vertical inflorescence was acropetalous but the flowers were distinctly protogynous, so flowers with newly receptive stigmas appeared on the inflorescence above those with dehiscing anthers. A number of small insects visited B. bullii; bees in the family Halictidae (Augochlorella striata and Dialictus spp.) were most common. When insects moved between gender phases within inflorescences, they moved up more often than down (61% versus 39% of observations, respectively) but this difference was only marginally significant. Most visits were to male-phase flowers only, and this preference was more pronounced for pollen-foraging insects than for nectar-foraging insects. B. bullii was self-compatible, so its flowering characteristics potentially could result in considerable self-pollination. However, an average of 38% of the lowermost flowers opened before any pollen was available on the same inflorescence; these solo females had a high probability of outcrossing (though fruit set was relatively low in the bottom portion of the inflorescence). Upper flowers may also be outcrossed because downward insect movement was not uncommon. Therefore protogyny in B. bullii may not necessarily lead to more selfing than would protandry.     

Observations of the floral biology ofPrasophyllum odoratum (Orchidaceae,Spiranthoideae)

Prasophyllum odoratum is a vernal, nectariferous, terrestrial orchid that flowers profusely six to eight months following cyclical fires that disrupt sclerophyll woodlands. The morphology of the column and pollinarium is indicative of taxa placed within the subfam.Spiranthoideae. The orientation of the pollinaria to the stigma appears to prevent mechanical self-pollination. Both cross- and self-pollination appear to be effected by insects that forage within the brightly-colored, scented, non-resupinate flowers. Ants and drosophilid flies remove nectar, but do not appear to transport pollinaria between flowers. The primary pollinators are polytrophic flies in the fam.Syrphidae and opportunistic male bees in the genusLeioproctus (Colletidae). Approximately 52% of the flowers on a raceme set seed. The comparatively short floral tube ofP. odoratum reflects the dependence of this species on short-tongued insects to effect successful dispersal of pollinaria.     

Pollination ecology ofOxalis violacea (Oxalidaceae) following a controlled grass fire

Vernal grass fires may encourage profuse flowering in clonal, colonies ofOxalis violacea. Long-styled colonies appear to be more floriferous than short-styled colonies and set a greater number of capsules. Individual flowers of both morphs live one or two days, change position on their respective pedicels and advertise nectar concealed at the base of the floral throat. AlthoughDiptera, Hymenoptera, andLepidoptera forage for nectar, bees (Andrenidae,Anthophoridae, Halictidae, andMegachilidae) probably make the only effective pollen transfers between the two morphs. Both male and female bees may transport pollen of both morphs and short-tongued bees (e.g.,Augochlorella spp.,Dialictus spp.) may be more common but as effective as pollinators as long-tongued bees (e.g.,Calliopsis andreniformis andHoplitis spp.). The conversion rate of flowers into capsules is only 13–17%. The spreading style in the short-styled morph is interpreted as an adaptation restricting insect-mediated, self-pollination but encouraging bee-stigma contact during nectar foraging.     

Flowering phenology,pollen flow and fruit production in the andean shrub Befaria resinosa

Summary In the eastern Andes of Colombia, the shrub Befaria resinosa (Ericaceae) has peaks of flowering that are separated by extended periods of low flower production. The effect that these fluctuations in flower production have on pollen flow was investigated by using fluorescent dye as a pollen analog. Dye applied to open flowers was dispersed over long distances more often during low flower production than during high flower production. Whether enhanced pollen dispersal during flowering lows is of benefit to individual plants is not clear. The proportion of flowers that set fruit is positively correlated with flower abundance, negating the possibility that increased pollen dispersal results in a higher rate of fruit production due to outbreeding effects. It is also difficult to attribute the pattern of fruit production to changes in pollinator visitation rates, which are negatively correlated with flower abundance in the case of hummingbirds and not correlated at all with flower abundance in the case of insects. An opportunistic, large-bodied hummingbird (Colibri coruscans) visits B. resinosa during high flowering and may be a particularly effective pollinator, accounting for some of the increase in the proportion of flowers setting fruit. Rainfall is positively correlated with flower production and may be an important factor in shaping flowering phenology, but it is not significantly correlated with the proportion of flowers setting fruits. The possibility that low-level flowering may counteract inbreeding that results from peak flowering is discussed.     

Pollen limitation in three sympatric species ofVaccinium (Ericaceae) in the Upper Ardennes, Belgium

The reproductive success of three co-flowering species ofVaccinium (V. myrtillus, V. vitis-idaea andV. uliginosum) was studied in one heathland of the Upper Ardennes, Belgium, during three years (1988–1990). The purpose was to examine whether pollen limitation, flower position and flowering phenology may influence patterns of fruit set in these three sympatric species. I quantified fruit and seed set following supplementary hand-pollinations and compared this to natural fruit set. On the same plants, I also quantified fruit and seed set in relation to the spatial position of the flowers on the ramet and their temporal sequence of blooming. Hand-pollination had no significant effect on fruit set inV. vitis-idaea andV. uliginosum, but significantly increased seed number per fruit in 1989. InV. myrtillus both fruit and seed set were increased by supplementary pollination, but significantly in only one year. Analyses of position effects revealed that the fruits in the lower positions in the ramet did not mature preferentially and did not contain more seeds inV. uliginosum and inV. vitis-idaea. Flowering phenology also had no significant effect for these species. InV. myrtillus hand-pollinated flowers showed a seasonal decline in seed number, and control (naturally pollinated) flowers showed a seasonal increase in fruit set. Fruit and seed set appear to be pollen-limited rather than resource-limited inV. uliginosum. In the two other species, unfavorable weather (frosts) could be a more important cause of low fruit and seed set.     

Flowering phenology of <Emphasis Type="Italic">Ulex europaeus</Emphasis>: ecological consequences of variation within and among populations

Reproductive phenology of gorse (Ulex europaeus L., Genisteae, Fabaceae) is unusual in that the onset and duration of flowering vary greatly among individuals within populations: some plants initiate flowering in autumn or winter and continue flowering through spring, others initiate flowering in early spring. To understand the origin of this diversity and its ecological consequences, we investigated flowering phenology of randomly sampled individuals from five different natural populations in Brittany (France). Reproductive success was evaluated for individuals with contrasting flowering patterns, from 16 natural populations. Flower production, pod production, seed production and seed predation were estimated. Plants initiating flowering in spring produced larger numbers of flowers and pods over a shorter period than plants flowering from winter to spring, which produced few flowers and pods at a time but over a longer period. Pod production of long-flowering plants did not differ significantly between winter and spring, but their pods were more intensively attacked by seed predators in spring than in winter. We discuss our results in relation to biotic and abiotic parameters. We postulate that long-flowering can be interpreted as a bet-hedging strategy, spreading the risk of pod failure (rotting or freezing) in winter and of seed predation in spring.     

The foraging behaviour of a nectar feeding marsupial,Petaurus australis

Summary The foraging behaviour of non-flying nectar feeding mammals has been examined rarely. The exudivorous yellow-bellied glider (Petaurus australis) was observed to feed extensively (70% of the total feeding observation time) on the nectar of all species of Eucalyptus present at a site in southeastern Australia. Gliders harvested nectar, and presumably pollen also, whenever eucalypt flowers were available and selected trees with 2–3 times as many flowers as that on trees randomly selected along a transect. The abundance of flowering trees varied temporally and, at times when few flowering trees were present, gliders chose trees with fewer flowers than at times when flowering trees were abundant. When flowering trees were superabundant or scarce, there was no relationship between the number of flowers in a tree and the duration of visits by gliders. However, at intermediate levels of abundance, the amount of time a glider spent in a tree was related to the number of flowers in a tree. Gliders devoted 90% of the time outside their dens to foraging and the above relationship is suggested to reflect two foraging options which maximize net energy gain for different abundances of flowering trees. Although gliders spent considerable lengths of time in individual trees feeding, initial deposition of cross pollen when gliders first arrive in a tree may be substantial and thus, may provide significant amounts of outcrossing for these eucalypts.     

Reproductive biology ofFrangula alnus (Rhamnaceae) in southern Spain

Various aspects of the reproductive biology of the perennial hermaphroditeFrangula alnus Mill. were studied in two populations located in the province of Cádiz, southern Spain. Flowering extends from the second week of May to early July. The small, whitegreenish, entomophilous flowers are incompletely protandrous and last 8–10 days, but pollen transfer takes place only on days 1–3. A very weak, pleasant odour along with nectar and pollen attract over 45 insect species, of which 21 are probable pollinators. These are mainlyDiptera but also includeHymenoptera and the unusual (as flower visitors)Mecoptera. Reproduction is exclusively sexual and strictly xenogamous, with pollen transfer depending solely on insect vectors. Although flower morphology and individual flower phenology do not fully prevent self-pollination, and geitonogamy can easily take place, the level of autogamy was negligible. Therefore, some self-incompatibility mechanism is operative in this species. Only 2.8% of open-pollinated flowers set fruit. At the flower level, fruit initiation was apparently limited by availability of cross-pollen, which in turn seemed influenced by the structure of the population. The seed/ovule ratio in ripe fruits was ca. 50%. Predispersal (maternal) reproductive success (percent ovules becoming filled seeds) was 1.42%. For mature individuals this corresponded to ca. 430 to 1560 potential offspring per year.     

Flowering biology ofGeonoma irena andG. cuneata var.sodiroi (Arecaceae)

The phenology and flowering of two sympatric understory palms from western Ecuador, until recently regarded as conspecific, is described.Geonoma irena Borchs. flowers throughout the year. Anthesis lasts 11–14 weeks per inflorescence, with overlapping male and female phases. Flowers open in the midmorning, and are visited mainly by meliponid and halictid bees.Geonoma cuneata var.sodiroi (Burret)Skov flowers from December to April, with a distinct peak in Feburary. Anthesis lasts 6–8 days per inflorescence, with non-overlapping male and female phases. Flowers open at dawn, and are visited mainly by drosophilid and sphaerocerid flies. The flowering pattern of the two species match different specific behavioural features of their insect visitors. The study provides an example of how differences in reproductive biology may act as an important barrier to gene flow between related, co-occurring taxa.     

A supplementary contribution of ants in the pollination of an orchid, Epipactis thunbergii, usually pollinated by hover flies

It has been controversial how extensively ants contribute to pollination, and we evaluated the contribution of the Japanese carpenter ant, Camponotus japonicus, to the pollination of an orchid, Epipactis thunbergii. Two-year field studies revealed that (1) the ant workers foraged even in cool/cloudy conditions and accordingly visited orchid flowers more frequently (about 40% of all the visitors) than hover flies, the principle pollinators (10–20%), and that (2) the flower-visiting ants occasionally removed pollinia from the anther and then delivered pollen onto the stigmatic surface of other flowers, although self-pollination might frequently occur in the consecutive visits of flowers within an inflorescence. An artificial pollination experiment with pollinia which had been transferred to the ant integument showed that (3) the treated flowers produced as many fruits and seeds as control flowers. We concluded that C. japonicus workers could actually pollinate E. thunbergii flowers and their relative importance as pollinators appeared to be largely dependent on the abundance of flower-visiting workers or weather conditions during the flowering period, which mainly determined the availability of hover flies.     

Contrasting breeding systems in twoEriotheca (Bombacaceae) species of the Brazilian cerrados

The pollination biology and breeding systems ofEriotheca pubescens andE. gracilipes have been studied. These two species occur as trees in cerrado vegetation, the neotropical savannas of Central Brazil, with partially sympatric distributions. They have similar phenology and floral structure, although the flowers ofE. pubescens are larger. Both species have nectar flowers pollinated by largeAnthophoridae bees but the main pollinators of each species differ in size. The species have markedly different breeding systems: late-acting self-incompatibility inE. gracilipes and apomixis stimulated by pollination inE. pubescens.     

Pollen and nectar as a reward in the basal epidendroid Psilochilus modestus (Orchidaceae: Triphoreae): A study of floral morphology, reproductive biology and pollination strategy

Psilochilus modestus Barb. Rodr. is a basal epidendroid orchid occurring in both the semi-deciduous and Atlantic rain forests of the state of São Paulo, southeastern Brazil. This species presents a perfect flowering synchrony within populations, since all the mature buds of each plant open simultaneously in the morning hours of the same day. These flowers are available only for 1 day and are pollinated by several species of small solitary and social native bees. These bees exploit both pollen and nectar as a reward. The bees collecting pollen promote a higher fruit set and perform mainly self-pollination while those collecting nectar, which are less numerous, are responsible for an increase in cross-pollinations. P. modestus is self-compatible but pollinator dependent. Natural fruit set (open pollination) is low when compared with the numbers obtained under manual self- and cross-pollination. Low fruit set in natural conditions is related to deficient pollen transfer, and pollinator inefficiency seems to be the main factor. Some factors, such as the small amount of nectar produced, the low number of flowers per inflorescence and their availability for 1 day only added to the perfect flowering synchrony seem to be responsible for the increase of cross-pollinations. The offering of both pollen and nectar as a reward can represent a transitional condition in basal Epidendroideae. Based on floral morphology, reward production and pollinator behavior, the relationship of P. modestus with the basal and most derived groups within Orchidaceae is discussed.     

Fruit set in a deceptive orchid: The effect of flowering phenology,display size,and local floral abundance

We investigated the effect of flowering time, display size, and local floral density on fruit set in Tolumnia variegata, a pollination-limited orchid that offers no reward to its pollinator(s). During 1990, natural variation in flowering time, display size, and fruit set were monitored in 508 plants at one locality in Puerto Rico. The following season, orchid floral abundance per host tree (Randia aculeata) was manipulated to investigate its effect on fruit set. Four floral abundance treatments were established (700, 500, 300, and 100), each replicated four times. Flowering time was the most important trait affecting fruit set. The proportion of plants setting at least one fruit was significantly high early and late in the season, but low during the flowering peak. Thus, strong disruptive selection differential on flowering phenology was found. Display size had little effect on fruit set. A weak, but significant disruptive selection differential on display size was found. Orchid floral abundance per host tree had a significant effect on fruit set. Early in the season, T. variegata flowers with intermediate number of conspecific flowers exhibited a greater probability of setting fruit than those in host trees with fewer or more flowers. Our results show that flowering phenology may be evolutionarily unstable, possibly a consequence of the deception pollination system. Furthermore, a deception strategy would be relatively unsuccessful in populations where plants are found in either very dense or sparse patches.     

Pollination by hummingbirds and bees in eight syntopic species and a putative hybrid of Ericaceae in Southeastern Brazil

We report on flowering phenology, floral morphology, pollinators, and nectar for eight species and a putative natural hybrid belonging to Agarista, Gaultheria and Gaylussacia that occur syntopically in a montane area. The campanulate to tubular flowers of eight out of nine Ericaceae taxa are primarily pollinated by either hummingbirds or bees. Flowering overlaps in all species but slight differences of floral shape, colour, and nectar characterize pollination by each pollinator group. Differences in floral traits are not large enough to exclude secondary pollinators. Thus, either the main pollinators of a species belonging to its syndrome, or secondary pollinators of a species belonging to different syndromes, may allow for inter-specific crosses.     

Male-biased sex ratio and promiscuous pollination in the dioecious island treeLaurus azorica (Lauraceae)

Pollination ofLaurus azorica (Lauraceae), a dioecious Macaronesian tree, was studied. Male and female trees had the same size distribution. The population had 2.5 times as many male trees as females. In addition, males produced more flowers, and their inflorescences lasted longer. Individual flower lifetime and length of flowering season were the same in both sexes. Between the years of observation, one tree changed sex. Pollinators wereHalictinae bees and the flyTachina canariensis. The bees collected pollen and nectar and the fly collected nectar from both sexes. Both species visited other plants as well. The evolution of breeding systems inLauraceae is discussed.     

矮紫金牛的开花生物学与繁育系统研究

矮紫金牛(Ardisia humilis)是优良的野生观赏植物。为探究该植物开花生物学与繁育系统特征,促进其杂交选育与园林应用,该研究以同质园引种的矮紫金牛为对象,对其开花物候、访花昆虫种类及访花行为进行观测,采用花粉离体萌发法和联苯胺-过氧化氢法,对花粉活力与柱头可授性进行检测,结合配子显微观测法和控制性授粉实验,对其繁育系统进行分析。结果表明：(1)花期为5月中下旬至6月中上旬,盛花期在5月底,单花、单株和群体水平的花期分别为1、17～20、25 d。(2)开两性花,雌蕊先熟,与雄蕊成熟期部分重叠,柱头可授性滞至雄蕊凋谢后1 d。(3)杂交指数(OCI)值为4,花粉/胚珠比(P/O)值为5.61×10³,显示其繁育系统以异交为主,部分自交亲和,需要传粉者。(4)自然授粉的结实率最高(平均52.96%),其次是自花授粉(52.29%)和人工异株授粉(50.33%),三者差异不显著(P> 0.05),但均显著高于人工同株授粉的结实率(28.67%)(P<0.05),显示矮紫金牛不仅异交亲和性强,还具有很强的自动自花授粉能力。(5)主要传粉昆虫包括隧蜂科...     

Flower development and reproductive continuity in MediterraneanRuscus aculeatus L. (Liliaceae)

Summary Ruscus aculeatus is a subandroecious species widespread in Mediterranean environments. Our studies on floral differentiation show that the unisexual flowers pass through a stage in which both androecial and gynoecial primordia are initiated. The hypothesis that dioecy has arisen secondarily from hermaphroditism is discussed. Data on flowering phenology of Mediterranean populations ofR. aculeatus showed it has a long flowering season (about 7 months). This phenology is similar to that of the Mediterranean species originated before the development of the Mediterranean climate. Members of the family Ruscaceae where present in Laurasia during the tropical Tertiary and the present study on flower and fruit morphology and reproductive phenology reveals forR. aculeatus a list of characters generally reported for tropical species. Small and greenish flowers, fleshy fruits, few large seeds, and resprouting capacity, together with long flowering season and continuous availability of ripe fruits, occur all together inR. aculeatus. It constitutes a tropical reproductive syndrome which might have survived the climatic fluctuations of the Quaternary, the establishment of the Mediterranean climate, and the present anthropogenic disturbs.     

Pollination system of Holcoglossum rupestre (Orchidaceae): A special and unstable system

The pollination system of Holcoglossum rupestre was studied in northwestern Yunnan. The species is self-compatible but pollinator-dependent and offers nectar as a reward to visitors. A species of beetle, Hybovalgus bioculatus Kolbe, is identified as the pollinator among all visitors observed. The beetles carried the pollinia in two different positions, i.e. on the buttock and the foreleg, and pollinated the flowers by two different mechanisms. The analysis suggests that Holcoglossum rupestre and its pollinator may be in an unstable pollination relationship. The natural fruit set is low, which is attributed to the low visiting frequency of pollinator and the effective mechanism to prevent self-pollination.