Visit Inflorescences Research Articles

Sexual and natural selection on pollen morphology in Taraxacum.

Spiny pollen has evolved independently in multiple entomophilous lineages. Sexual selection may act on exine traits that facilitate male mating success by influencing the transfer of pollen from the anther to the body of the pollinator, while natural selection acts to increase pollen survival. We postulated that relative to sexual congeners, apomictic dandelions undergo relaxed selection on traits associated with male mating success. We explored sexual selection on exine traits by measuring the propensity for Taraxacum spp. pollen to attach to hairs of flower-visiting bumblebees (Bombus spp.) or flies (Diptera: Syrphidae and Muscoidea) and assessed natural selection by testing whether pollen traits defend against consumption. Pollen picked up by bumblebees exhibited a narrower subset of spine-spacing phenotypes, consistent with stabilizing selection. Flies picked up larger pollen from flowers than expected at random. Surveys of corbiculae (pollen basket) contents from foraging bumblebees and feces of flies showed that pollen grains consumed by both kinds of visitors are similar in spine characteristics and size to those produced by the donor. When bees visit inflorescences of apomictic T. officinale, they pick up pollen with spine-spacing phenotypes above the mean and shifted toward those of sexual T. ceratophorum. We demonstrate that traits under sexual selection during pollen pickup vary among pollinators, while natural selection for pollen defense is nil in T. ceratophorum. In hybrid zones between apomictic and sexual dandelions, pollen traits place apomictic donors at a dispersal disadvantage, potentially reinforcing reproductive isolation.

Visual and olfactory floral cues related to ambophilous pollination systems in Poaceae

Abstract Usually considered anemophilous, grasses (Poaceae) have been the subject of few studies that recorded insects visiting their flowers. Such visitors, with wind, could act as pollen vectors in a possible ambophilous system. Since colour and scent are floral cues attracting pollinating insects, we aimed to provide the first insights into how these cues could be involved in the attraction of pollinators by grasses. Chloris barbata, Paspalum maritimum (with two morphotypes), P. millegrana and Urochloa plantaginea were studied. We determined the role of each pollen vector (wind and insect) and we registered the frequency of floral visitors. Also, we characterized the colour reflectance of glumes, anthers and stigmas and we determined the colour space in the bee colour hexagon and the chemical composition of floral scents. The floral structures of each species reflect colour differently and are perceived differently by pollinators. Furthermore, the volatile organic compounds detected are similar to those found in entomophilous species. In two of the grass species, we registered eight species of visitors, including bees, wasps and flies. Overall, wind was the most important vector for reproductive success. Insects, however, may induce wind pollination by creating pollen clouds when they visit inflorescences.

New evidence for mammal pollination of Protea species (Proteaceae) based on remote-camera analysis

Flower visitation by small mammals is difficult to observe directly on account of their sensitivity to human presence and the nocturnal activity of some species. Their role in pollination has, thus, been inferred mostly from analysis of fur and faecal pollen loads of field-trapped animals. The development of motion-activated remote cameras allows for unprecedented insights into natural behaviours of small mammals on flowers. We used remote cameras to assess the identity of flower visitors, and the frequency and timing of their visitation to flower heads of four poorly studied Protea species (P. cordata, P. decurrens P. scabra and P. subulifolia) that were predicted to be rodent-pollinated on the basis of floral traits. Camera footage revealed that small mammals (typically three to six rodent species per Protea species) were frequent visitors to flower heads over one flowering season, making up 100% of visits to P. cordata and P. subulifolia, 98% of visits to P. decurrens, and 90% of visits to P. scabra. Rodents that are known pollinators of other ground Protea species, such as Acomys subspinosus, Micaelamys namaquensis and Rhabdomys pumulio, were observed to make contact with reproductive parts of the flowers, but further work would be required to demonstrate unequivocally that they are the main pollen vectors of these species. Mus minutoides was recorded for the first time to frequently visit inflorescences of P. subulifolia. Other visitors included genets that visited P. scabra inflorescences to lick nectar off florets, and birds that were relatively infrequent visitors to all species. Together with recent literature, the present study has shown that the utilisation of remote cameras in pollination studies provides an efficient, discreet method for observing vertebrate flower-visiting behaviour.

Development and Maintenance of a Cross-mixed Mating System in the Orchid Bulbophyllum orientale

Outbreeding is usually advantageous because inbreeding suffers from depression. Nevertheless, mixed mating is very common in nature. We found two co-existing plant types, self-compatible and self-incompatible, in populations of the orchid Bulbophyllum orientale. The floral parts of this plant form a device to promote cross-pollination. Rancid substances are excreted to lure pollinators to the labellum, and pollens are attached to pollinators through a delicate mechanism. Given that many inflorescences and flowers are present on a clone and each inflorescence, respectively, pollinating insects may continuously visit inflorescences of the same clone and flowers of the same inflorescence but rarely continuously visit different populations separated by large distances. Consequently, self-compatible plants produce seeds from both crossing and selfing, and self-incompatible plants only bear crossing seeds. Thus, a crossmixed mating system is created in the population. Individuals capable of producing both crossed and selfed seeds have better chances in natural selection. The strict crossing system is broken down, and a cross-mixed mating system consisting of both mixed mating and strict crossing is formed. The cross-mixed mating system fluctuates with varying behavior of pollinating insects. The mixed mating system is favored because a population has many clone individuals and because each individual has many multi-flower inflorescences in B. orientale. The partial strict crossing is retained, and it can counteract the latent harm caused by selfing and assist in the maintenance of this cross-mixed mating system. The successful evolution of flowering plants is demonstrated by the mode of attraction for pollinating insects, the smart use of the cross-pollinating facility, and the tradeoff between crossing and mixed mating.

Signal honesty and cost of pollinator rewards in Dalechampia scandens (Euphorbiaceae).

Most species of Dalechampia vines (Euphorbiaceae) attract bee pollinators with terpenoid resins secreted by a gland-like structure in the inflorescence. In some species, pollinating bees appear to preferentially visit inflorescences (blossoms) with large resin-producing glands, whereas in other species bees preferentially visit blossoms with large involucral bracts. In this study, the reliability of bract and gland size as signals of the quantity of resin produced in one species, D. scandens, was assessed. Whether resin secretion has a cost with respect to the number or mass of the seeds produced by a blossom was also examined. Measurements were made of bract size, gland size and the amount of resin secreted by blossoms of D. scandens maintained in a common environment, and the relationships between these traits were analysed. Resin production was also manipulated, and the effects of the manipulation were tested on seed set and seed mass. The amount of resin produced was better predicted by the size of the gland than by the size of the bract. Furthermore, when the effect of gland size was accounted for, bract size only weakly predicted the amount of resin produced. Neither an increase in resin secretion (by daily removal of the resin) nor a decrease (by removal of the resin gland) affected seed set or seed mass detectably, but resin production correlated positively with mean seed mass at the individual level once the size of the resin gland was accounted for. Gland size is a better indicator of the amount of reward than bract size, although the latter remained an honest signal of the quantity of resin produced. Resin secretion has no detectable cost in terms of seed production, but may be condition dependent, as suggested by a positive correlation with seed mass at the individual level.

Clonal growth and its effects on male and female reproductive success in Prunus ssiori (Rosaceae)

AbstractClonal growth can increase not only floral display but also geitonogamy and may affect sexual reproduction both positively and negatively. A clonal woody species, Prunus ssiori, was partially self‐incompatible according to a pollination experiment. Its main pollinators, bumble bees, were often observed to consecutively visit inflorescences within a tree. Clone identification revealed that its genets formed mutually exclusive patches. These features suggest frequent geitonogamous pollination. In a 6.24‐ha plot, 212 trees belonged to 59 genets, and 42 genets consisted of a single tree, whereas the rest contained two or more clonal trees. The largest genet had 65 trees and occupied 0.4 of a hectare. Fruit set was measured in 127 inflorescences sampled from nine maternal trees at the center of the plot. Paternal genets of 107 of their 300 seeds were assigned in the plot using microsatellites. There were no selfed seeds. Male reproductive success (the probability that individual trees of each genet sired a seed) increased as tree size increased, as the distance between the trees and maternal trees decreased, when the genet did not contain the maternal trees, and when the genet consisted of a single tree. Female reproductive success (fruit set in individual inflorescences of each maternal tree) increased as the within‐tree geitonogamy index, which reflected the frequency of pollination within the maternal tree, decreased. These results suggest that clonal growth reduces male reproductive success, at least, in P. ssiori, because of pollen discounting.

Synchronization between temporal variation in heat generation, floral scents and pollinator arrival in the beetle‐pollinated tropical Araceae Homalomena propinqua

AbstractInflorescences of beetle‐pollinated plants, such as Araceae, show temporal heat generation, the role of which varies among plants. Homalomena propinqua is a common understory herb in the lowland dipterocarp forests of Borneo. Two species of beetle, Parastasia bimaculata Guerin (Scarabaeidae) and Dercetina sp. (Chrysomelidae), are known to visit inflorescences of this species and subsequently transfer its pollen. In this study, to examine the role of heat generation by inflorescences of H. propinqua, especially as an attractant of pollinators, measurements of the temperature of spadices, behavioral experiments with beetles and chemical analyses of floral scents were carried out. As a result, spadices of H. propinqua exhibited heat generation from 06:30 hours (dawn) until 09:30 hours on both the first and second days of flowering, and this paralleled the arrival of the beetle pollinators. Behavioral tests showed that both beetle pollinators were attracted to spadices significantly more than spathes. Floral scents of H. propinqua were composed of 18 compounds, the main one being 2‐butanol, a highly volatile low molecule compound. The amount of floral scents increased temporally between 07:00 hours and 08:00 hours on the first day of flowering, which was consistent with the arrival of pollinators and heat generation by the spadices. These results indicate that the heat generated by spadices may promote temporal volatilization of floral scents, especially highly volatile compounds such as 2‐butanol, and as a result temporally attracting beetle pollinators.

Aggregation of Micropterix maschukella moths on inflorescences of common elder: mating at foraging sites (Lepidoptera Micropterigidae)

We investigated mechanisms underlying distribution of an archaic moth, Micropterix maschukella, among inflorescences of the adult's principal food plant, common elder Sambucus nigra. Moths aggregate on certain inflorescences within a plant, preferring inflorescences at early stages of flowering. Females visit inflorescences to feed with pollen; they do not search for conspecific groups and even avoid densely populated inflorescences. In contrast, males visit inflorescences mainly for mating; they feed only seldom and preferentially land on inflorescences with high number of conspecific individuals. Mating was more frequent on inflorescences with higher density of moths. Mating strategy of morphologically archaic Micropterigidae, classified as ‘explosive breeding strategy’, has significantly deviated from pheromone-mediated location of females which is considered ancestral for the order Lepidoptera.

A weevil pollinating the Canary Islands date palm: between parasitism and mutualism.

Palm pollination systems are highly diverse, including by wind and by several different groups of insects. Many palm species are associated with more or less specific pollinating weevils that are also floral herbivores. For many such palms, the importance of these "palm flower weevils" as pollinators has not been examined. Here we describe a new ex situ method of demonstrating insect pollination when pollinator exclusion is not possible. We show that Neoderelomus piriformis beetles carry pollen and deposit it on the stigma of Phoenix canariensis. Up until now, pollination systems in Phoenix have been unclear, despite the economic importance of the date palm P. dactylifera. We demonstrate here that small weevils that visit inflorescences and often inconspicuously hide there could be efficient pollinators.

Foraging Behaviour of Marsupial Pollinators in a Population of Banksia spinulosa

Spool-and-line tracking was used to investigate the foraging behaviour of three marsupial species (Petaurus breviceps, Antechinus stuartii and Cercartetus nanus) which regularly visit inflorescences of the Australian native, Banksia spinulosa (Proteaceae). Although there were as many as 10 open inflorescences on a plant, 72% of movements by animals were to inflorescences on a different plant. Furthermore. nearly 70% of these movements were over 5 m in length, and movements ranged up to 59 m. Inter-plant movements were greater for P. breviceps than other species, particularly late in the flowering season when fewer inflorescences were available. This suggests that patterns of pollen flow in this population of B. spinulosa may vary spatially and temporally

Pollination in Geonoma macrostachys and Three Congeners, G. acaulis, G. gracilis, and G. interrupta

AbstractA continuous 15 month study of the floral ecology of four syntopic understorey palm species of Genoma was conducted in Amazonian Peru lowland rainforest.The spicate inflorescences of G. macrostachys, G. acaulis and G. gracilis are strictly protandrous and the plants are functionally dioecious. Data suggest that in G. macrostachys and G. acaulis pollination is based on a mimicry system, the pistillate flowers mimicking the staminate ones in colour, shape and scent. Pollen‐collecting meliponine bees (Hymenoptera, Apidae, Meliponinae) and pollen‐feeding syrphid flies (Diptera, Syrphidae) which visit inflorescences during both sexual stages are the pollinators of G. macrostachys. Geonoma acaulis is pollinated by small pollen‐feeding weevils (Coleoptera, Curculionidae, Derelomini) that visit male and female spikes.Additionally, in G. macrostachys another pollinator type, viz. euglossine bees (Hymenoptera, Apidae, Euglossinae), which are attracted and rewarded by both types of flowers may account for long‐distance pollination.The palm G. gracilis shows a very distinct pollination system. Although opportunistic insect visitors are attracted to the inflorescences of this species it seems to be mainly anemophilous because pollen becomes powdery during an thesis.The branched inflorescences of G. interrupta are also protandrous, but unlike the other species of Geonoma observed, staminate and pistillate anthesis of individual flowers are, for the most, overlapping. A broad spectrum of visitors is attracted (bees, wasps, flies, and beetles), which all may act as pollinators. Outcrossing is especially encouraged during the purely female phase at the end of the flowering cycle when there are no more staminate flowers in the inflorescence.Effects on the reproductive biology and population structure of different pollination systems and breeding system are discussed.

Pollination ecology of Yucca elata : An experimental study of a mutualistic association.

The pollination biology of a population of 250 Yucca elata (Liliaceae) plants was studied in southern New Mexico. Yucca elata and the prodoxid yucca moth Tegeticula yuccasella have a mutualistic association that is essential for the successful sexual reproduction of both species. However, a wide range of other invertebrate species visit flowers during the day and at night. Our aim was to quantify the role of yucca moths and other invertebrate visitors in pollination and fruit set, using manipulative field experiments. Inflorescences were bagged during the day or night (N=12 inflorescences) to restrict flower visitors to either nocturnal or diurnal groups. Yucca moths were active exclusively nocturnally during the flowering period and thus did not visit inflorescences that were unbagged during the day. None of the 4022 flowers exposed only to diurnal visitors set fruit, whereas 4.6% of the 4974 flowers exposed only to nocturnal visitors (including yucca moths) produced mature fruit. The proportion of flowers producing fruit in the latter treatment was not significantly different from unbagged control inflorescences. In a series of experimental manipulations we also determined that: (1) flowers opened at dusk and were open for two days on average, but were only receptive to pollen on the first night of opening; (2) pollen must be pushed down the stigmatic tube to affect pollination; and (3) most plants require out-cross pollination to produce fruit. The combination of these results strongly suggests that yucca moths are the only species affecting pollination in Y. elata, and that if another species was to affect pollination, it would be a rare event.