Variation in fruit- and seed set among and within inflorescences of Melampyrum roseum var. japonicum (Scrophulariaceae)

Abstract Variations in fruit set and seed set among and within inflorescences of the annual herb, Melampyrum roseum var. japonicum, were studied. Under natural conditions, although the mean fruit set was slightly different among inflorescences, the mean seedset was not significantly different among inflorescences within the plants. In constrast, within the inflorescences, the flowers located at a lower position of the inflorescence and which opened earlier showed higher fruit set than those at a higher position and which opened later. However, the seed set of matured capsules were not significantly different from each other, regardless of the position of flowers within the inflorescences. Patterns of the fruit- and seed set under open pollination indicated that variation in seed reproduction of M. roseum is due to variation in fruit production. The results of clipping experiments of flowers revealed that there was no functional limitation in seed production among flowers located at various positions within the inflorescence. It seemed that the variation in the fruit set within the inflorescences of M. roseum was not attributable to 'architectural effects'. Reduction of the number of flowers within the inflorescences resulted in an increase of fruit set and seed weight, indicating that the flowers in an inflorescence compete for resources. This phenomenon supports the 'resource competition hypothesis', and variation in fruit set within the inflorescence is attributable to competition among flowers within the inflorescence for limited resources. Consequently, it was concluded that, under natural conditions, the early blooming flowers located at lower positions of the inflorescences obtain more resources and produce more fruits than the late blooming flowers located at higher positions in M. roseum .     

山罗花和天柱山罗花四个居群的数值分析

对山罗花和天柱山罗花的4个居群的15项形态特征进行了数值分析。结果表明:形态性状在4个居群间均存在一定程度的变异,居群间变异系数的平均值从小到大排列为:天柱山居群(天柱山罗花)、天柱山居群(山罗花)、黄山居群(山罗花)、鹞落坪居群(山罗花);天柱山罗花与山罗花种间的形态差异已达到极显著水平,山罗花的3个居群间部分性状也具有极显著的形态差异;以形态特征为基础的Q-聚类分析可以把天柱山罗花和山罗花聚为两类,但山罗花(天柱山居群)和其他2个居群在较远处聚在一起,R-聚类分析发现了强正相关关系、弱正相关关系、弱负相关关系的性状。     

Variability of nectar production and composition in Linaria vulgaris (L.) Mill. (Scrophulariaceae)

 We studied nectar characteristics during the long flowering period (late June to end of November) in two populations of Linaria vulgaris (L.) Mill. spontaneously growing in the Botanical Gardens of Siena University (Tuscany, central Italy). The two populations were close to each other but they differed in blooming period. Plants of population 1 sprouted in May and flowered from the end of June to the end of September. Population 2 sprouted at the end of August and flowered from September to the end of November. Differences in nectar production and composition were found between and within populations. Flowers of population 1 produced a very small amount of nectar (not collectable) that remained on the nectary surface. The quantity of nectar increased in late September, when each flower produced 2–3 μl of nectar that flowed into the spur. Total sugar concentration was 175.8 mg/ml in young flowers. Flowers of population 2 produced 5–8 μl of nectar with a total sugar concentration of 200.9 mg/ml in the young stage. In bagged senescent flowers nectar volume decreased in both populations and nectar sugar concentration decreased down to 11.6 mg/ml in population 2 and increased up to 289.6 mg/ml in population 1. For both populations, the decrease in nectar volume in bagged flowers may have been due to water loss by evaporation. In population 2, the decrease in sugar concentration may have been due to nectar reabsorption that was never observed in population 1. Nectar variability is discussed in relation to insect visits and seed set. Received August 14, 2002; accepted December 17, 2002 Published online: June 2, 2003     

Pollination Ecology and Effect of Nectar Removal in Macleania bullata (Ericaceae)1

The floral syndrome of Macleania bullataYeo (Ericaceae) reflects its adaptation to hummingbird pollination. Its flowers, however, are subject to high levels of nectar robbing. I examined the floral visitor assemblage of M. bullata in a tropical montane wet forest in southwestern Colombia, focusing on the behavior of the visitors. I also tested for the presence of nocturnal pollination and the effects of nectar removal on new nectar production. The principal floral visitors were the nectar robbing hummingbirds Ocreatus underwoodii (19.1% of visits) and Chlorostilbon mellisugus (18.9%). Only two species of long–billed hummingbirds visited the flowers of M. bullata as “legitimate” pollinators: Coeligena torquata (14.7% of visits) and Doryfera ludoviciae (14.3%). The remaining visits constituted nectar robbing by bees, butterflies, and other species of hummingbirds. Nocturnal pollination took place, although fruit set levels were 2.4 times higher when only diurnal pollination was allowed as opposed to exclusively nocturnal pollination. Nectar robbers removed floral nectar without pollinating the flower. Treatments of experimental nectar removal were carried out to examine if flowers synthesize more nectar after nectar removal. Nectar removal increased the total volume of nectar produced by each flower without affecting sugar concentration. Thus, nectar robbing can impose a high cost to the plants by forcing them to replace lost nectar.     

Pollination Ecology and Endemic Adaptation of Pedicularis howellii Gray (Scrophulariaceae)

Abstract Pedicularis howellii , endemic to the Siskiyou Mountains of California-Oregon, is a root hemiparasite obligately dependent upon bumblebee pollinators that remove pollen by vibration from its short-tubed, nectarless, rostrate flowers, which reflect visible and ultraviolet (360nm) light attractive to Bombus foragers. All six Bombus species in the study area pollinated the plant, but only on P. howellii and P. racemosa were B. mixtus workers the most abundant pollinators among the seven bumblebee-pollinated plants studied, including Delphinium decorum, Dodecatheon jeffreyi, Penstemon newberryi, P. shastensis, and Phacelia heterophylla. Analysis of corbicular pollen loads of Bombus pollinators indicated that pollen foragers on Pedicularis species were less pollen-constant than all other bumblebee pollinators. Although P. howellii and P. racemosa blooming periods overlapped slightly, phenological isolation of blooming periods of plants sharing the same pollinators was not evident. Chemical soil analysis of its habitat and quadrat analysis of the population structure of Pedicularis howellii indicated that the plant grows in a moderately fertile forest soil and is restricted to the edge of forest canopy openings where sunlight favors development of plants to the flowering stage. The endemism of P. howellii is related to a similar "edge effect" survival of P. furbishiae in a boreal forest riparian habitat previously studied.     

Pollination system of the Pilosocereus leucocephalus columnar cactus (tribe Cereeae) in eastern Mexico

It has been suggested that there is a geographic dichotomy in the pollination systems of chiropterophilous columnar cacti: in intra‐tropical areas they are pollinated almost exclusively by bats, whereas in extratropical areas they are pollinated by bats, birds and bees. However, currently the studies are clumped both taxonomically (mainly Pachycereeae species) and geographically (mainly in the Tehuacan Valley and the Sonoran Desert). This clumping limits the possibility of generalising the pattern to other regions or cactus tribes. Only four of the 36 chiropterophilous cacti in Pilosocereus have been studied. Despite the tropical distribution of two Pilosocereus species, bees account for 40–100% of their fruit set. We examined how specialised is the pollination system of P. leucocephalus in eastern Mexico. As we studied tropical populations, we expected a bat‐specialised pollination system. However, previous studies of Pilosocereus suggest that a generalised pollination system is also possible. We found that this cactus is mainly bat‐pollinated (bats account for 33–65% of fruit set); although to a lesser degree, diurnal visitors also caused some fruit set (7–15%). Diurnal visitors were more effective in populations containing honeybee hives. P. leucocephalus is partially self‐compatible (14–18% of fructification) but unable to set fruit without visitors. Despite the variation in pollination system, P. leucocephalus shows more affinity with other columnar cacti from tropical regions than with those from extratropical regions. Although we report here that a new species of tropical Pilosocereus is relatively bat‐specialised, this Cereeae genus is more flexible in its pollination system than the Pachycereeae genera.     

Reproductive biology of the Red List species Polemonium caeruleum (Polemoniaceae)

The majority of flowering plants, including many rare and threatened species, are pollinated by animals, but little is known of pollination and breeding systems of many endangered species. Polemonium caeruleum (Polemoniaceae) is a red‐listed species and is regarded as dichogamous, self‐compatible and bee pollinated. However, some studies show that it is visited by a vast assemblage of anthophilous insects from many taxonomic orders and that breeding systems vary greatly between closely related taxa of this genus. Over a period of 3 years we investigated breeding system, dichogamy, nectar secretion and composition, insect visitations and pollen loads in flowers of P. caeruleum in north‐eastern Poland to determine whether the reproductive biology of the plant explains its rarity. Contrary to published data, our study plants were self‐incompatible and showed a high degree of outcrossing. Our experimental work confirmed the occurrence of protandry in this species, revealed that nectar is sucrose‐dominant and proline‐rich and, for the first time for Polemoniaceae, that nectar secretion and nectar sugar concentration in flowers of P. caeruleum is female‐biased. Although flowers were visited by at least 39 species of insects from five taxonomic orders, overall the plant exhibited many characters associated with bee pollination, and analysis of insect performance showed that bumblebees and honeybees are the key pollinators; occasionally hoverflies and butterflies may also be involved. We conclude that, in terms of pollination system, P. caeruleum demonstrates high apparent generalization, but low realized generalization, and is a functional specialist, as most pollinators belong to a single functional group (guild). Its conservation status, at least in our study population, cannot be explained in terms of the biological properties of its breeding or pollination systems; rather, the present decline of the species is caused by habitat loss. However, if this process and bumblebee decline in Europe continue, P. caeruleum populations may diminish in numbers and density and, owing to the self‐incompatibility of the species, quickly become severely pollen‐limited, thereby accelerating further local extinctions. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 173 , 92–107.     

Pollination Ecology of Pedicularis punctata Decne. (Scrophulariaceae) in the Kashmir Himalaya

Abstract The pollination ecology of Pedicularis punctata was studied in the Pir Panjal Range of the Kashmir Himalaya in the summer of 1989. Its nectarless, rostrate, long-tubed flower was found to be pollinated exclusively by Bombus foragers vibrating pollen while the stigma contacted pollen in the pollinator's cervical crevice. Workers of Bombus tunicatus and B. flavothoracicus comprised 95% of its pollinators. Pollen-foraging fidelity of its pollinators was greatest where diversity of Bombus -pollinated plant species in three plant communities was least. Foragers on other plants carried virtually no Pedicularis pollen. P. punctata is a mid-season blooming species similar in its pollination syndrome to comparable species in other geographic regions. The enigmatic function of its long, nectarless corolla tube, even more exaggerated in other Asiatic species, requires further investigation.     

A Preliminary Study of the Pollination Ecology of Pedicularis (Scrophulariaceae) in Japan

Abstract An introductory study of the pollination ecology of six Japanese species of Pedicularis conducted in 1982 and 1983 indicated a close parallel between characteristics of floral mechanisms in Japan and those previously investigated in North America. Floral color, floral form, total dissolved solids in floral nectar, and polinator behavior on flowers of Japanese species are similar to those of North American species. Blooming phenology of Japanese species also corresponds to the North American sequence of long-tongued, nectar-foraging queen bumblebees (Bombus Latr.) pollinating nectariferous , earlier-blooming species nototribically and short-tongued, pollen-foraging workers pollinating nectarless, rostrate flowers of later-blooming ones sternotribically. Electrofocus analysis of peroxidase systems in two Japanese species indicated considerable intrapopulational heterozygosity. Nectar component analysis of two transboreal species indicated intraspecific differences in kinds of sugars between widely disjunct Japanese and North American populations. A tentative conclusion is that the Japanese and North American Pedicularis floras have evolved in a parallel manner from Himalayan migrants, while their transboreal elements are in process of vicariant diversification.     

Pollination Ecology of Pedicularis megalantha D. Don (Scrophulariaceae) in the Himachal Himalaya

Abstract In the summer of 1990, the pollination ecology of Pedicularis megalantha was studied in the montane-subalpine spruce-fir forest zone (2750-3050 m) on the north slope of Mt. Huttoo at Narkanda, Himachal Pradesh, in the Indian Himalaya. Its yellow, long-tubed, nectarless flower with a curled rostrum overarched by a broad, inverted lower corolla lip was pollinated exclusively by Bombus albopleuralis and B. tunicatus workers hanging inverted from the corolla and vibrating pollen from introrse anthers concealed within the galea and releasing pollen through a small ventral opening in the galea base. The stigma, protruding from the tip of the rostrum, contacted pollen deposited on the ventral side of the insect's thorax. Corbicular pollen loads from P. megalantha pollinators indicated equal numbers of monolectic and oligolectic foragers. P. megalantha appeared to suffer from competition for pollinators by Cynoglossum wallichii at one site but to be favored in a mixed plant community with nectariferous species offering a forage resource complementary to Pedicularis pollen. As in P. punctata , the long, nectarless corolla tube of P. megalantha appears to function in extending the rostrate vibration pollination mechanism beyond the plant's foliage, which would interfere with its function. It is not an adaptation for nectar-foraging lepidopteran pollinators. P. megalantha was also found to be a root hemiparasite.     

Pollination biology and breeding system of Zeyheria montana (Bignoniaceae)

The reproductive biology of Zeyheria montana was studied through field observations of flower visitors and floral events, controlled manual pollinations, and observations of pollen tube growth and ovule penetration by fluorescence microscopy. Analysis of secretory areas of the nectar chamber was made by flower dissections and histology of serial sections. The flower lasted 6–8 days, but pollen exposure and stigma receptivity occurred only up to the end of the first and second days, respectively. Pollination was effected by several species of hummingbirds, especially Colibri serrirostris. The flowers present a rudimentary, non-functional disc, and secretion of nectar is performed by corolla-borne glandular trichomes. Only hand cross-pollinated and natural-pollinated flowers set fruits. Artificially self-pollinated and non-pollinated flowers dried off after anthesis without presenting any swelling of the ovary. Almost all the ovules in selfed and crossed pistils were penetrated 96 h after pollination. However, a delay in ovule penetration in self-pollinated pistils was verified, which indicates the occurrence of late-acting self-incompatibility.We are grateful to Fundo de Apoio ao Ensino e à Pesquisa (UNICAMP) for financial support, and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for the fellowship granted to the first author (this work is part of a Ph.D. thesis presented to UNICAMP, Campinas, SP, Brazil).     

Roles of species-preferential seed dispersal by ants and endozoochory in Melampyrum (Orobanchaceae)

Aims Melampyrum pratense and M. subalpinum are two myrmecochorous species, which possess similar habitat requirements and frequently occur together. Despite this, their population sizes differ markedly. Melampyrum pratense populations are usually very large, whereas M. subalpinum has rather small and isolated populations. We suggest that such an imbalance might be partially influenced by the difference in ant-mediated seed-removal rates. Genus Melampyrum is considered to be exclusively myrmecochorous, though to achieve the recent distribution of some Melampyrum species during the Holocene myrmecochory would be highly insufficient. We suggest that endozoochory takes place in the long-distance migration, whereas myrmecochory is important for the removal of seeds on a local scale.Methods For seed-preference analysis, M. pratense and M. subalpinum mixed seed samples were placed around Formica polyctena anthills. After a period of time, the remaining seeds of both species were counted for each sample. The results were analysed by analysis of variance and generalized linear mixed-effect model. To test myrmecochorous removal distances, M. pratense seeds were covered with fluorescent dactyloscopic powder and placed in the vicinity of a large ant trail. The area around the starting plot was searched in the dark using UV LED torchlight 7h after the beginning. The distance from the starting plot was measured for each seed found. Birds, rodents, leporine and a ruminant were fed with M. pratense seeds and fresh plants to test the possibility of endozoochorous dispersal of the species. Animal droppings were searched for intact seeds.Important findings Our field studies show that from mixed seed samples, containing both species, ants significantly preferred the seeds of M. pratense. This may be one of factors that has positive influence on M. pratense success in seed dispersal on mixed stands and consequently in the colonization of favourable sites. Experiments focusing on ant-mediated dispersal distance revealed that F. polyctena ants are able to move seeds over a distance of 36 m in only 7h. This distance is among the furthest known myrmecochorous removals of forest plant seeds. A new Melampyrum seed disperser Oligolophus tridens (Opiliones) was observed repeatedly. Our pilot study documented that Melampyrum seeds are able to pass through the digestive tract of a cow intact. This suggests that large ruminants such as deer, bison or forest-grazing livestock may function as important long-distance dispersers of Melampyrum species.     

Nocturnal Versus Diurnal Pollination Success in Isertia laevis (Rubiaceae): A Sphingophilous Plant Visited by Hummingbirds

Abstract: Isertia laevis (Rubiaceae) possesses flowers with traits typical for the pollination syndrome of sphingophily. Diurnal flower observation showed that nine different hummingbirds (Trochilidae) and one flower piercer (Coerebidae) were frequent visitors. Their activity on the flowers peaked in the morning hours. Very low nectar volumes were found in the morning (8.00 h) in unbagged flowers. Nectar volumes, however, reached their peaks (27 μl) at night (2.00 h) in bagged, as well as in unbagged flowers. At night few individuals of sphingids were observed. Pollination experiments showed that flowers presented to nocturnal pollinators from 18.00 h to 6.00 h had low fruit set (14 %) but high seed set (59 %). Flowers accessible from 6.00 h to 18.00 h for diurnal flower visitors showed high fruit set of 63 % but low seed set of 14 %. This suggests that pollination of individual flowers is less effective during daytime. Regarding relative reproductive success, i.e., efficiency of pollination defined as fruit set x seed set, both diurnal and nocturnal pollinators, however, are equally successful. We conclude that frequently occurring, but not very effective pollinators contribute substantially to seed production, when the expected pollinators are scarce.