Enhanced UV-Reflection Facilitated a Shift in the Pollination System of the Red Poppy, Papaver rhoeas (Papaveraceae)

Evolutionary change is considered a major factor influencing the invasion of new habitats by plants. Yet, evidence on how such modifications promote range expansion remains rather limited. Here we investigated flower color modifications in the red poppy, Papaver rhoeas (Papaveraceae), as a result of its introduction into Central Europe and the impact of those modifications on its interactions with pollinators. We found that while flowers of Eastern Mediterranean poppies reflect exclusively in the red part of the spectrum, those of Central European poppies reflect both red and ultraviolet (UV) light. This change coincides with a shift from pollination by glaphyrid beetles (Glaphyridae) to bees. Glaphyrids have red-sensitive photoreceptors that are absent in bees, which therefore will not be attracted by colors of exclusively red-reflecting flowers. However, UV-reflecting flowers are easily detectable by bees, as revealed by visual modeling. In the North Mediterranean, flowers with low and high UV reflectance occur sympatrically. We hypothesize that Central European populations of P. rhoeas were initially polymorphic with respect to their flower color and that UV reflection drove a shift in the pollination system of P. rhoeas that facilitated its spread across Europe

The Carpenter Bee Xylocopa pubescens as an Agricultural Pollinator in Greenhouses

Many greenhouse crops depend on bees for pollination. Global declines of honeybee populations, and their limited efficiency in pollinating some greenhouse food-plants, motivate the search for additional pollinators. We evaluated the carpenter bee X. pubescens, a local species to Israel, as a pollinator of greenhouse-grown honeydew melons, in comparison to honeybees. We recorded the bees' daily and seasonal activity patterns in relation to floral nectar levels, frequencies and durations of flower visits, and fruit quantity and quality. The bees' daily foraging schedule on melon did not correlate with nectar yield and nectar production patterns by the flowers. Visit durations per flower were shorter for X. pubescens than for honeybees. Pollination by both bees resulted in similar fruit mass and seed numbers, but X. pubescens pollination increased fruit set threefold as compared to honeybee pollination. We conclude that X. pubescens can effectively pollinate melons in enclosures

Variability in Nectar Production and Yield, and their Relation to Pollinator Visits, in a Mediterranean Shrub

Nectar yields (standing crops) in flowers within an individual plant are often highly variable. This variability may be a by-product of the foraging activity of insect pollinators. Alternatively, plants may be selected to produce highly variable rewards to reduce consecutive visitation by risk-averse pollinators, thus diminishing within-plant pollen transfer. This study evaluated the roles of pollinator control vs. plant control over nectar variability in the bee-pollinated shrub Rosmarinus officinalis L. We sampled nectar production, yield and pollinator visits in three shrubs of one population over 17 days during one blooming season. Nectar production rates were highly variable (CV=1.48), and increased after rainy days. Nectar yields were even more variable (CV=2.16), and decreased with increasing temperatures. Pollinator visit rates decreased with variability in nectar yields, increased with flower number per shrub, and were unaffected by variability in nectar production rates. Repeated sampling of marked flowers revealed no correlation between their nectar yields and production rates. These findings support the role of reward variance in reducing pollinator visits, but suggest that plants are not in complete control of this variability. Rather, plant-generated variability can be modified by intensive foraging activity of pollinators. Such pollinator control over nectar variability is likely to reduce the selective advantage of plant-generated reward variation. Plant-controlled variability may provide evolutionary advantage when pollinator activity is insufficient to generate reward variation.Geitonogamy; Honeybee; Rosmarinus officinalis; Nectar variability

Pollination ecology of the red Anemone coronaria (Ranunculaceae): honeybees may select for early flowering

Large red bowl-shaped flowers characterize the Mediterranean “poppy guild” plants, and were suggested to reflect convergence for beetle pollination. However, the earliest-blooming species in this guild, Anemone coronaria (L.), starts flowering about a month before beetle emergence. Early flowering can be adaptive if the plant receives sufficient pollination by other means during this period. We investigated A. coronaria’s pollination prospects throughout its flowering season by monitoring its flowering phenology, the composition of the surrounding insect community, and insect visitors. Clear protogyny precluded self pollination, and anthesis occurred gradually over several days. Released pollen was quickly collected by insects, suggesting no major role for wind pollination. Beetles, flies and bees were trapped at the study site throughout the flowering period. Honeybees were the main anemone visitors during the first seven weeks of flowering, and were joined by Glaphyrid beetles in the remaining three weeks. Early- and late-blooming flowers had similar female reproductive success. We propose that effective pollination by honeybees may allow anemones to bloom in early spring and thereby reduce competition for pollinators with later-blooming species. Our results support previous evidence for pollination of red flowers by bees, and for the importance of generalization in pollination interactions in heterogeneous environments.

The Signaling Function of an Extra-floral Display: What Selects for Signal Development?

The vertical inflorescences of the Mediterranean annual Salvia viridis carry many small, colorful flowers, and are frequently terminated by a conspicuous tuft of colorful leaves ("flags") that attracts insect pollinators. Insects may use the flags as indicators of the food reward in the inflorescences, as long-distance cues for locating and choosing flowering patches, or both. Clipping of flags from patches of inflorescences in the field significantly reduced the number of pollinators that arrived at the patches, but not the total number of inflorescences and flowers visited by them. The number of flowers visited per inflorescence significantly increased with inflorescence size, however. Inflorescence and flower visits rates signific antly increased with patch size when flags were present, but not after flag removal. 6% of the plants in the study population did not develop any flag during blooming, yet suffered no reduction in seed set as compared to flag-bearing neighboring individuals. These results suggest that flags signal long-distance information to pollinators (perhaps indicating patch location or size), while flower-related cues may indicate inflorescence quality. Plants that do not develop flags probably benefit from the flag signals displayed by their neighbors, without bearing the costs of flag production. Thus, flagproducing plants can be viewed as altruists that enhance their neighbors' fitness. Greenhouse-grown S. viridis plants allocated = 0.5% of their biomass to flag production, and plants grown under water stress did not reduce their biomass allocation to flags as compared to irrigated controls. These findings suggest that the expenses of flag production are modest, perhaps reducing the cost of altruism. We discuss additional potential evolutionary mechanisms that may select for the maintenance of flag production.

The Use of Numerical Information by Bees in Foraging Tasks

The ability of invertebrates to perform complex cognitive tasks is widely debated. Bees utilize the number of landmarks en-route to their destination as cues for navigation, but their use of numerical information in other contexts has not been studied. Numerical regularity in the spatial distribution of food occurs naturally in some flowers, which contain a fixed number of nectaries. Bees that collect nectar from such flowers are expected to increase their foraging efficiency by avoiding return visits to empty nectaries. This can be achieved if bees base their flowerdeparture decisions on the number of nectaries they had already visited, or on other sources of information that co-vary with this number. We tested, through field observations and laboratory experiments, whether bees adapt their departure behavior to the number of available food resources. Videorecorded observations of bumblebees that visited Alcea setosa flowers with five nectaries revealed that the conditional probability of flower departure after five probings was 93%. Visit duration, the spatial attributes of the flowers and scent marks could be excluded as flower-leaving cues, while the volume of nectar collected may have guided part of the departure decisions. In the laboratory the bees foraged on two patches, each with three computer-controlled feeders, but could receive only up to two sucrose-solution rewards in each patch visit. The foragers gradually increased their tendency to leave the patches after the second reward, while the frequency of patch departure after the first reward remained constant. Patch-visit duration, nectar volume, scent marks and recurring visit sequences in a patch were ruled out as possible sources of patch-leaving information. We conclude that bumblebees distinguish among otherwise identical stimuli by their serial position in a sequence, and use this capability to increase foraging efficiency. Our findings support an adaptive role for a complicated cognitive skill in a seemingly small and simple invertebrate.