EFFECTS OF ENVIRONMENTAL STRESS ON COMPONENTS OF REPRODUCTION IN CLARKIA UNGUICULATA

The effects of stress on reproduction in Clarkia unguiculata were investigated by monitoring flower number, seed number and seed wt after subjecting plants to drought and heavy fruit loads, and by monitoring seed number after pollinating overage flowers. Fewer main-stem flowers were produced in drought stressed plants than in non-stressed plants. Drought stress did not affect overall seed numbers and seed wt in 1981, but did significantly affect seed number and wt in different flower age classes. Overall seed numbers were not affected by drought stress in 1982, but seed wt was significantly lower in plants with stressed ovules. Fewer flowers but more seeds per pollination were produced by plants in which all or ½ the flowers were pollinated than by plants in which ¼ or 1/6 of the flowers were pollinated. Seed wts were lowest in plants with a full fruit load and in fruits produced late in the growth cycle. Seed number was variable but high following pollination of flowers with 1–7 day old stigmas, and much lower in flowers with older stigmas.     

Reproductive biology of two Himalayan alpine gingers (Roscoea spp., Zingiberaceae) in China: pollination syndrome and compensatory floral mechanisms

According to the concept of pollination syndromes, floral traits reflect specialisation to a particular pollinator or set of pollinators. However, the reproductive biology of endemic, and often specialised, plants may require increased attention as climate change accelerates worldwide. Species of Roscoea endemic to the Himalayan region have striking orchid-like flowers with long corolla tubes, suggesting pollination by long-tongued insects. Until now, the reproductive biology of species of Roscoea has been poorly documented. We investigated the floral biology, breeding system and pollination ecology of R. cautleoides and R. humeana, from Hengduan Mountains, a global biodiversity hotspot in southwest China. We also tested whether floral longevity increases pollination success. Pollination experiments showed that the two species were self-compatible and depended on insects for fruit production. Over several flowering seasons we did not observe any potential pollinators with long tongues that matched the corolla tube visiting flowers in centres of distribution. The principal pollinators observed were pollen-collecting generalist bees, with low visitation frequencies. In general, members of the ginger family are characterised by short-lived (usually 1 day) flowers, but flowers of R. cautleoides and R. humeana last 8 and 6 days, respectively. Removing stigmas decreased fruit set in both study populations. Our results suggest that the original pollinators may have been long-tongued insects that are now absent from the Chinese Himalayas because habitats have responded to climate change. However, long-lived and self-compatible flowers, coupled with the presence of generalist pollinators, are traits that have allowed these gingers to reproduce and continue to persist in the alpine habitats.     

Pollination ecology of the Cerrado species Eschweilera nana (Lecythidaceae subfam. Lecythidoideae)

Eschweilera nana is pollinated by a guild of pollinators consisting of mostly bees. Effective pollinators are large bees able to force their way into the closed androecium to access nectar. The morphology of the flowers diminishes self pollination and promotes cross-pollination. Although many pollinators make diurnal visits to the flowers, fruit set was very low in comparison with the number of flowers produced. Breeding system tests yielded only two fruits, one produced by xenogamy and another one in the control test. The results of this study are consistent with studies of other Cerrado plants pollinated by guilds of insects and support the conclusion of other pollination studies of Lecythidaceae that fruit set is low in comparison with the high numbers of flowers produced.     

The impacts of pollination mode,plant characteristics and local density on the reproductive success of a scarce plant species, <Emphasis Type="Italic">Salix arbuscula</Emphasis>

Pollination failure represents one stage at which sexual reproduction of plants may be limited. It is therefore important to understand the pollination mechanism of the plant and how this may be affected by plant and population characteristics. This study examined the reproductive biology of a scarce montane willow species, Salix arbuscula, as part of a programme to determine ecological strategies for the conservation of montane willow scrub, an endangered habitat in the UK. The relative importance of insect and wind pollination, and the role of plant characteristics including plant size, catkin length, number of flowers and local density in determining reproductive success (number of fruit set) were investigated in three populations. Insect exclosures were used to determine the pollination mechanism. Our results suggest that S. arbuscula is predominantly insect-pollinated. In naturally pollinated plants, catkins with a higher proportion of ripe fruit were longer. Plants with more than two males in the local area and unbrowsed plants had a higher proportion of ripe fruit per catkin. The extent of wind pollination was very low, but differed between populations. The success of wind-only pollination was dependent on the number of males nearby, indicating that local density is more important in this type of pollination. Pollination mechanism and fruit set varied between the three populations observed, demonstrating the importance of multi-site comparisons. The number of males in the surrounding area had a positive effect on fruit set in both types of pollination, suggesting that Allee effects are likely to be operating in this species.     

Can ants equal honeybees as effective pollinators of the energy crop Jatropha curcas L. under Mediterranean conditions?

Jatropha curcas L. is the subject of many research and breeding programs concerned with its potential as an oil crop for biodiesel production. Despite an increasing amount of information regarding this relatively new crop, pollination requirements of this plant are largely neglected. The aim of the study was to evaluate the relative significance of ants and honeybees as potential pollinators of J. curcas grown under Mediterranean conditions. Jatropha curcas plants bloomed throughout the summer and fall, peaking twice, in early summer and late fall. During this period, the plants were visited by 70 species of insects representing 45 families from seven orders, with most species rarely being observed. Ants and Honeybees were the most common species, accounting for >95% of all flower visits. The foraging behavior of the honeybees followed the pattern of bloom phenology, especially during the summer, and mostly promoted cross‐pollination. Ants on the other hand, mostly promoted self pollination showing no such correlative behavior, reacting often too late to nectar availability, and were highly susceptible to climatic changes. Pollinator exclusion treatments revealed that during summer, fruit and seed sets, as well as seed size and oil and protein contents, were relatively similar for ant and bee‐pollinated flowers. During fall, however, reproductive success of bee‐pollinated flowers was relatively high (66%), while fruit set of ant‐pollinated flowers was significantly reduced from 71 to 11%. In conclusion, while both groups are equal in their pollination effectiveness in the summer, during the fall the honeybees are almost the sole pollinators of the plant. Based on bloom phenology and pollination activity data, the honeybees are responsible for the pollination of more than 80% of the annual reproductive potential of J. curcas, under Mediterranean conditions.     

Pollinators and Reproductive Success of the Wild Cucurbit Cucurbita maxima ssp. andreana (Cucurbitaceae)

Abstract: We studied the reproductive success and pollinators of Cucurbita maxima ssp. andreana in different disturbed habitats where it grows naturally. Data were obtained from three populations. One grew within a soybean crop, the other within a corn crop, and the third in an abandoned crop field. Cucurbita maxima ssp. andreana is an annual vine with a flowering period from December to April. Male flowers appear first, thereafter female and male flowers appear together. Flower lifetime (9 h) was similar in male and female flowers. The pollinator guild was comparable for the three populations but some differences in the frequency of the insect species were observed. Native bees were the main pollinators in the population in the abandoned field, while beetles pollinated the populations in crop fields. These differences were not linked with the pre-emergent reproductive success, fruit and seed set, or fruit quality. This is a self-compatible plant. Fruit and seed set and fruit traits (total mass, width and length of fruits, number of seeds per fruit, and seed mass) did not show significant differences between hand-cross and hand-self pollinated flowers. This wild cucurbit is a generalist with respect to pollinator guild, and flower visitors seem to be highly efficient in pollen transference. Cucurbita maxima ssp. andreana is well adapted to disturbed habitats because plants ripened fruits successfully, regardless of the group of insects visiting flowers.     

Pollination intensity and potential seed set in Passiflora vitifolia

Summary Initial seed set and fruit set were pollen-limited in a Costa Rican population of Passiflora vitifolia, a self-incompatible species with 200–350 ovules per flower. Pollination intensity was measured by counting the number of allogamous pollen grains on stigmas of the large one-day flowers. Hand-pollinations demonstrated that 25–50 pollen grains are required for fruit set, and >450 are needed for maximum seed set, with a pollen:seed ratio of about 1.6:1.0. Hummingbirds (Phaethornis superciliosus) delivered sufficient allogamous pollen for maximum seed set to only 28% of the flowers examined. Naturally pollinated flowers yielded fewer fruits and fewer seeds per fruit than those pollinated by hand. Most pollen transferred by humming-birds was self-incompatible; emasculated flowers yielded higher seed set than flowers with intact anthers. Visitation rates did not provide a good index of effective pollination.There were significant differences in ovule number, maximum seed set, and maximum per cent seed set among individual vines. More than half of an individual's flowers failed to set fruit, whether pollinated by birds or by hand. In this population, maximum reproductive potential may be limited by maternal resources for fruit development, but seed set varies with pollination intensity. Pollen-limited seed set may be a disadvantage of self-incompatibility, especially in species with many-seeded fruits.     

PATTERNS OF FRUIT PRODUCTION IN A NEOTROPICAL ORCHID: POLLINATOR VS. RESOURCE LIMITATION

Patterns of growth, and of flower and fruit production, were monitored over two years in a population of the orchid Aspasia principissa Reichb. f. in central Panama. Observations and experimental manipulations were used to determine the relative importance of pollinator and resource limitation on fruit production. Within a season, fruit production was limited by pollinator availability. Fruit set for hand-pollinated flowers was over six times greater than that for naturally pollinated flowers. However, in plants that produced more than one fruit, fruit size declined in subsequent fruits, indicating that resources could limit seed production within a season. Plants producing fruits in 1986, on average, produced smaller shoots and inflorescences in 1987 relative to plants that flowered but produced no fruit in 1986. Thus, plants are likely to be resource limited over their lifetimes. Most individuals of reproductive size (82.5%) did not produce fruit over a three-year period. The reproductive dominance of a few individuals in this population of Aspasia principissa may have important implications for understanding the population structure of the species and the high species diversity of orchids.     

Pollen viability and limitation of seed production in a population of the circumpolar cushion plant, Silene acaulis (Caryophyllaceae)

Pollen viability among genders and limitation of female seed production in a natural trioecious population of the circumpolar cushion plant Silene acaulis was examined. Pollen viability was estimated by an in vitro pollen germination experiment. Both male and hermaphrodite flowers displayed large variation in pollen viability (0–53% in hermaphrodite and 0–54% in male flowers). There was a significant difference between genders in pollen viability: male plants had on average higher pollen viability than hermaphrodite plants. Resource and pollen limitation of seed production was studied by an experiment consisting of three treatments; (I) hand-pollination and removal of all other flowers on the cushion, (II) hand-pollination without removal of other flowers, and (III) open pollination without removal of flowers. Hand-pollination increased seed production, whereas removal of flowers had no effect on seed production. Abortion of pollinated ovules during seed development and seed mass did not differ among treatments. To control for effect of fruit number on seed production, data from naturally pollinated individuals was used. There was a positive correlation between both total number of seeds and fruit number, mean seed number per fruit and fruit number, respectively. These results indicate that seed production of 5. acaulis is mainly limited by pollen availability whereas resource competition between fruits is not important as a limiting factor. The possible role of male quality differences between genders and pollen limitation of seed production for maintenance of trioecious reproductive systems is discussed.     

The effect of pollination on resource allocation among sexual reproduction,clonal reproduction,and vegetative growth in <Emphasis Type="Italic">Sagittaria potamogetifolia</Emphasis> (Alismataceae)

In order to evaluate the effects of pollination on resource allocation in the marsh herb Sagittaria potamogetifolia, experimental manipulation of pollination efficiency on the pattern of resource allocation was accessed by the proportion of dry weight measurements of sexual, vegetative, and clonal organs. In trials where half of the flowers were pollinated, a significant increase of resource allocated to sexual production and decrease to vegetative production resulted compared to plants that received no pollination. In trials where pollination was 100%, these two reproductive components showed the same trend, but less dramatically. This may support the idea that the trade-offs would be more pronounced when the resource was scarce. Besides, a higher inflorescence production with a lower fruit reproduction occurred as a consequence of decreased pollination level. This increased inflorescence production may be a mechanism to promote outcrossing by enhancing floral attraction or by synchronizing reproductive activity with insect pollinators. Examination for possible trade-offs in resource allocation revealed that there was also a trade-off caused by pollination between fruits plus flowers and bulbils production, which might have detrimental effects on the survival of individuals and populations, but promotes outcrossing and genetic variability.     

Self‐pollination and parthenocarpic ability in developing ovaries of self‐incompatible Clementine mandarins (Citrus clementina)

This study aimed to determine if self‐pollination is needed to trigger facultative parthenocarpy in self‐incompatible Clementine mandarins (Citrus clementina Hort. ex Tan.). ‘Marisol’ and ‘Clemenules’ mandarins were selected, and self‐pollinated and un‐pollinated flowers from both cultivars were used for comparison. These mandarins are always seedless after self‐pollination and show high and low ability to develop substantial parthenocarpic fruits, respectively. The time‐course for pollen grain germination, tube growth and ovule abortion was analyzed as well as that for carbohydrates, active gibberellins (GA₁ and GA₄), auxin (IAA) and abscisic acid (ABA) content in the ovary. ‘Clemenules’ showed higher pollen grain germination, but pollen tube development was arrested in the upper style 9 days after pollination in both cultivars. Self‐pollination did not stimulate parthenocarpy, whereas both un‐pollinated and self‐pollinated ovaries set fruit regardless of the cultivar. On the other hand, ‘Marisol’ un‐pollinated flowers showed greater parthenocarpic ovary growth than ‘Clemenules’ un‐pollinated flowers, i.e. higher ovule abortion rate (+21%), higher fruit set (+44%) and higher fruit weight (+50%). Further, the greater parthenocarpic ability of ‘Marisol’ paralleled higher levels of GA₁ in the ovary (+34% at anthesis). ‘Marisol’ ovary also showed higher hexoses and starch mobilization, but lower ABA levels (?64% at anthesis). Self‐pollination did not modify carbohydrates or GA content in the ovary compared to un‐pollination. Results indicate that parthenocarpy in the Clementine mandarin is pollination‐independent with its ability to set depending on the ovary hormone levels. These findings suggest that parthenocarpy in fertile self‐incompatible mandarins is constitutively regulated.     

Persistently low fruiting success in the Mediterranean pipevine Aristolochia baetica (Aristolochiaceae): a multi-year study

Low fruit set is common in many plant species and may be caused by a variety of factors, such as predation, resource limitation or deficient pollination, or it may be an evolutionary strategy. In this paper, we investigate factors that affect fruit set in Aristolochia baetica (Aristolochiaceae), a Mediterranean pipevine found in southwest Spain. Fruit production was monitored in two populations over 4 years (2002-2005), and the causes of flower or fruit loss were determined. Experimental hand-pollinations were performed, and germinated pollen grains on the stigmas of open-pollinated flowers were quantified. Fruit set was always very low (4-14%). Floral abscission initially reduced reproductive output by more than 50%; then herbivory (6-12%) and fruit abortion (8-26%) caused further reductions. Given that the number of efficiently pollinated flowers was always higher than that of ripe fruits, and that xenogamous hand-pollination did not increase fruit set in relation to open-pollination, the final fruit production of A. baetica seems not to be pollen-limited. Fruit abortion of effectively pollinated flowers supports the idea that resource availability limits fruit set. In A. baetica, fruit abortion could lead to mate selection of the best quality fruits. Moreover, the initiated fruits that finally abort could also satiate predators, contributing to increase progeny fitness.     

Dioecious plants are more precocious than cosexual plants: A comparative study of relative sizes at the onset of sexual reproduction in woody species

The reproductive capacities of dioecious plant species may be limited by severe pollen limitation and narrow seed shadows for the two reasons. First, they are unable to self‐pollinate, and seed production occurs only with pollinator movement from males to females. Second, only 50% of the individuals in populations contribute to seed production. Despite these handicaps, dioecious plants maintain their populations in plant communities with cooccurring cosexual plants, and no substantial difference in population growth rates has been found between dioecious and cosexual plants. Hence, dioecious plants are thought to mitigate these disadvantages by adopting ecological traits, such as insect pollination, animal‐dispersed fleshy fruits, and precocious flowering. We studied the relationship between flowering and plant size in 30 woody species with different sex expressions, leaf habits, fruit types, and maximum plant sizes. The study site was located in an evergreen broad‐leaved forest on the island of Honshu, Japan. A phylogenetic linear regression model showed that dioecious species tended to mature at smaller sizes than did cosexual taxa. At the population level, given equal plant densities and reproductive efforts, the precocity of dioecious plants could serve as one of the factors that mitigate the limitations of pollen and seed‐shadow handicaps by increasing the density of reproductive individuals in the population. At the individual level, smaller size of onset of flowering may play a role in enhancing reproductive success over a lifetime by increasing reproductive opportunities. We discussed the possible effect of the relationship between precocity and some ecological traits of dioecious plants, such as small flowers pollinated by unspecialized insects, fleshy fruit dispersed by animals, and their preferential occurrence in the tropics and in island habitats. The universality of precocity among dioecious plants should be investigated in diverse plant communities. Such studies will increase our understanding of the evolution of plant breeding systems.     

Phylogeny and radiation of pollination systems in DISA (Orchidaceae)

We studied the patterns of adaptive radiation in Disa, a large orchid genus in southern Africa. A cladogram for 27 species was constructed using 44 morphological characters. Pollination systems were then mapped onto the phylogeny in order to analyze pathways of floral evolution. Shifts from one pollination system to another have been a major feature of the evolutionary diversification of Disa. Unlike many plant genera that are pollinated mainly by a single group of insects, radiation in Disa has encompassed nearly all major groups of pollinating insects; in all, 19 different specialized pollination systems have been found in the 27 species included in this analysis. Another striking pattern is the repeated evolution of broadly similar pollination systems in unrelated clades. For example, butterfly-pollinated flowers have evolved twice; showy deceptive flowers pollinated by carpenter bees, twice; long-spurred flowers pollinated by long-tongued flies, four times; night-scented flowers pollinated by moths, three times; and self-pollination, three times. This suggests that a few dominant pollinator species in a region may be sufficient to generate diversification in plants through repeated floral shifts that never retrace the same pathways.     

Corolla herbivory, pollination success and fruit predation in complex flowers: an experimental study with Linaria lilacina (Scrophulariaceae)

BACKGROUND AND AIMS: Herbivory on floral structures has been postulated to influence the evolution of floral traits in some plant species, and may also be an important factor influencing the occurrence and outcome of subsequent biotic interactions related to floral display. In particular, corolla herbivory may affect structures differentially involved in flower selection by pollinators and fruit predators (specifically, those ovopositing in ovaries prior to fruit development); hence floral herbivores may influence the relationships between these mutualistic and antagonistic agents. METHODS: The effects of corolla herbivory in Linaria lilacina (Scrophulariaceae), a plant species with complex flowers, were considered in relation to plant interactions with pollinators and fruit predators. Tests were made as to whether experimentally created differences in flower structure (resembling those occurring naturally) may translate into differences in reproductive output in terms of fruit or seed production. KEY RESULTS: Flowers with modified corollas, particularly those with lower lips removed, were less likely to be selected by pollinators than control flowers, and were less likely to be successfully visited and pollinated. As a consequence, fruit production was also less likely in these modified flowers. However, none of the experimental treatments affected the likelihood of visitation by fruit predators. CONCLUSIONS: Since floral herbivory may affect pollinator visitation rates and reduce seed production, differences among plants in the proportion of flowers affected by herbivory and in the intensity of the damage inflicted on affected flowers may result in different opportunities for reproduction for plants in different seasons.     

Genetic engineering of parthenocarpic fruit development in tomato

Parthenocarpy was engineered in two genotypes of Lycopersicon esculentum Mill. by using the DefH9-iaaM chimeric gene. The parthenocarpic trait consists of fruit set and growth in the absence of fertilization. Seedless parthenocarpic fruits were obtained from emasculated flowers, and fruits with seeds from pollinated flowers. All parthenocarpic tomato plants analysed expressed the DefH9-iaaM gene during flower development. The fruit set percentage of emasculated transgenic flowers was similar to that of control plants. In 7 out of 8 independent transgenic plants, the fresh weight of fruits derived from pollinated or emasculated flowers did not significantly differ from that of fruits obtained by pollination of the control plants. The pH of the parthenocarpic fruit was generally unaffected and the soluble solid concentration was either unchanged or increased. Thus, the DefH9-iaaM gene is a genetic tool that might be used to improve tomato productivity.     

Day–night fluctuations in floral scent and their effects on reproductive success in <Emphasis Type="Italic">Lilium auratum</Emphasis>

We examined the contribution of diurnal and nocturnal pollination to male and female reproductive success in Lilium auratum. Plants were bagged for either 12 h during the day or at night to allow either only nocturnal or only diurnal visitors to forage throughout the flowering period. We found that there was no significant difference in the seed:ovule ratio among diurnally pollinated, nocturnally pollinated, or control flowers. However, in terms of male reproductive success, it was more advantageous for the plants to be pollinated both diurnally and nocturnally: the numbers of pollen grains remaining in diurnally pollinated or nocturnally pollinated flowers were significantly greater than those in control flowers. The total amount of floral volatiles of L. auratum was significantly higher at night than during the day. The constituents of floral scent of all time series examined were mostly monoterpenoids, many of which serve as attractants for nocturnal hawkmoths. Such nocturnally biased floral scent emission of L. auratum might achieve male reproductive success by attracting nocturnal visitors, which may suggest that the relative contribution of floral scent in this species is biased towards male reproductive success.     

Variability in Pollen Load: Implications for Reproduction and Seedling Vigor in a Rare Plant, Silene douglasii var. Oraria

Habitat fragmentation can markedly influence the levels of pollen deposition and seed production in natural populations, and rare plants may be especially susceptible to any associated reductions in pollen quantity and quality. In order to ascertain the potential for pollen limitation of maternal fitness in a rare plant, Silene douglasii var. oraria, which is endemic to western coastal prairies, we counted ovules and measured conspecific and heterospecific pollen deposition on stigmas collected from open-pollinated plants. We further investigated the effect of increasing pollen intensity on fruit production, seed number and weight, as well as several measures of progeny vigor. Three levels of outcross pollen were added to plant stigmas for comparison with autogamous and open pollination in the largest naturally occurring population. Both seed and fruit production were significantly greater (P<0.05) for supplemented versus nonsupplemented stigmas, but flowers receiving different levels of pollen addition were statistically indistinguishable. Seed germination and seedling survival were also lowest for the offspring of nonsupplemented flowers; however, in natural populations, opportunities for pollen competition are very limited since open-pollinated flowers averaged fewer viable pollen grains than ovules. Seed production was equivalent for open- and autogamously pollinated flowers in 1996, indicating that natural pollen transfer may have involved mostly self pollen. Overall, the low reproductive success of var. oraria likely reflects both low pollen quantity and quality. Multiyear empirical studies of pollen intensity in field populations are needed so that we can better understand the fitness consequences of pollen limitation in rare perennials.     

A multi-year study of factors affecting fruit production in Aristolochia paucinervis (Aristolochiaceae)

Pollen limitation, resource limitation, fruit abortion, and predation have all been proposed as factors explaining low fruit set in hermaphroditic plants. We conducted a 5-year study combining field observations and pollination experiments to determine the causes of the low fruit set in Aristolochia paucinervis, a Mediterranean species with a specialized pollination system in two populations in SW Spain. Fruit initiation was markedly low, and between 28.6 and 75.0% of the flowering stems did not initiate any fruit. In most flowers, the number of germinated pollen grains was less than the number of ovules, and supplemental pollination significantly increased fruiting, indicating deficient pollination. In A. paucinervis, autonomous self-pollination seems to be a decisive factor in fruit production because the number of germinated pollen and the fruit set from flowers bagged before anthesis were similar to those in free-pollinated flowers. Only in 2005 did flowers that were successfully pollinated outnumber ripened fruits, suggesting that other factors limit fruiting. We found a significant positive correlation between tuber mass and fruit set. Deficient pollination and lack of resources could explain the low fruit set, but the relative consequences seem to vary spatially and temporarily.     

Early blooming's challenges: extended flowering season, diverse pollinator assemblage and the reproductive success of Gynodioecious Daphne laureola

BACKGROUND AND AIMS: The scarcity and unpredictability of active pollinators during late winter in temperate areas tends to favour extended flowering seasons and increased floral longevity in early blooming species, which are usually pollinated by diverse sets of insects. Daphne laureola is a gynodioecious woody perennial that flowers from January to April in southern Spain, a period characterized by cold temperatures, frequent rains and irregular snowfalls. METHODS: Pollinators were excluded at four different times during the flowering season in order to determine the effect of decreased exposure to pollinators on fruit set in female and hermaphrodite individuals. The role of nocturnal and diurnal pollination on reproductive success in each gender was simultaneously evaluated by selective exclusion. KEY RESULTS: A 50 % reduction in the flowering period decreased fruit set of females by 50 %, whereas the corresponding decrease in self-compatible hermaphrodites was only approx. 25 %. Day-active hymenopterans and lepidopterans were infrequent visitors, and nocturnal pollinators were inefficient, suggesting that pollen beetles, Meligethes elongatus, were the main pollinators of D. laureola in the study region. CONCLUSIONS: Beetles were less abundant in pollenless females, although discrimination did not apparently result in pollination limitation of female reproduction. A preference of beetles for sunny locations emphasized the relevance of abiotic conditions for pollination of this early blooming shrub.