Possible Mechanisms for the Formation of Flower Size Preferences by Foraging Bumblebees

Abstract

Large flowers often contain larger nectar rewards, and receive more pollinator visits, than small flowers. We studied possible behavioral mechanisms underlying the formation of flower size preferences in bumblebees, using a two‐phase laboratory experiment. Experimentally naive Bombus terrestris (L.) foraged on artificial flowers that bore either a large (3.8 cm diameter) or a small (2.7 cm diameter) display of a uniform color. Only flowers of one display size contained nectar rewards. We changed the display color and the locations of large and small flowers in the second experimental phase. We recorded the bees' choices in both phases. Almost half of the bees (41%) made their first visit to a small flower. The bees learned to associate display size with food reward, and chose rewarding flowers with >85% accuracy by the end of each experimental phase. Some learning occurred within the bees' first three flower visits. Learning of the size–reward association was equally good for large and small displays in the first experimental phase, but better for small displays in the second phase. Formation of size–reward associations followed a similar course in both phases. This suggests that the bees did not apply their experience from the first learning phase to the new situation of the second phase. Rather, they treated each phase of the experiment as an independent learning task. Our results suggest that associative learning is involved in the formation of preferences for large displays by bees. Moreover, bees that had learned to prefer large displays in one foraging situation may not transfer this preference to a novel situation that is sufficiently different. We propose that this feature of the bees' behavior can select for honest advertising in flowers.

Pollinators exert natural selection on flower size and floral display inPenstemon digitalis

“…2; Harder & Johnson, 2009) and fits with the general hypothesis that pollinators select for larger flowers because they are more conspicuous and ⁄ or may be associated with larger rewards (e.g. Blarer et al, 2002). Natural selection for larger displays is also common ( Fig.…”

Flower Preferences of the Wrocław Botanical Garden Bumblebees (Bombus spp.)

“…In later foraging stages, the bumblebees did not choose the same size of flowers. The above information suggests that bumblebees are guieded by odour and colour, rather than a certain flower size (Blarer et al, 2002).…”

Getting to the start line: how bumblebees and honeybees are visually guided towards their first floral contact

“…Under the principle that the evolution of floral signals is tied to pollinator perception, and that in nature floral size is possibly predictive of reward, Blarer et al (2002) considered the possibility that there might be a preference for large flowers over smaller ones on the very first visit by bumblebees (B. terrestris). If such a preference were found, it would be important in terms of the evolution of floral displays: plants that honestly signalled their reward availability (see Armbruster et al, 2005) would be invasible by cheaters.…”

“…If such a preference were found, it would be important in terms of the evolution of floral displays: plants that honestly signalled their reward availability (see Armbruster et al, 2005) would be invasible by cheaters. Such a preference was not found, though with experience, bees were capable of associating floral size with reward (Blarer et al, 2002). In a more recent study, we used artificial flowers that consisted of two blue perpendicular acrylic sheets perched on top of a container that trapped bees that entered.…”