Bumblebees Get a Foothold

a fluffy, black, yellow and white striped bumble bee sits in a flower to pollinate

Biological Strategy

Sharp-leaved cancerwort

AskNature Team

Image: Thanasis Papazacharias / Pixabay / Free non-commercial use

Respond to Signals

To interact with its environment, a living system must not only sense a variety of signals, but also respond to them. To be energy- and material-efficient, those responses must be appropriate to the signal. This generally requires sensing thresholds to trigger an appropriate level of response (for example, hiding under a shrub versus running away to avoid a predator). Response strategies are tied to a specific signal and often have a response threshold, which determines how strong a signal must be to warrant expending energy to respond. One example is a plant that lives in arid regions in South Africa. Its seed capsules remain closed until rainfall triggers them to open to release the seeds. But the plant only responds to a second rainfall, thus protecting against releasing its seeds before there is enough sustained water for them to grow.

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Flowering Plants

Clade Angiosperms (“receptacle seed”): Dandelions, oaks, grasses, cacti, apples

With 416 families containing some 300,000 known species, angiosperms are the most diverse group of plants, and they can be found around the globe in a wide variety of habitats. They are characterized by seeds that grow enclosed in ovaries, which are enclosed in flowers. The floral organs then develop into fruits of myriad kinds and dimensions, from simple seed casings on maples to elaborate fleshy growths like papayas. The oldest flower known from fossils, Montsechia vidalii, appeared during the Jurassic Period 130 million years ago. They are the primary food source for herbivorous animals, which in turn makes them the indirect food source for carnivores as well.

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The petals of flowers attract pollinators by providing non-slip surfaces via conical epidermal cells.

“Approximately 80% of angiosperms produce petals with similar conical epidermal cells (Kay et al. 1981), and numerous suggestions as to their function have been made. These include the possibilities that they enhance petal colour, act as a direct tactile cue, increase the temperature of the flower, influence scent production or release, or influence the wettability of the flower surface (Kay et al. 1981; Kevan and Lane 1985).” (Dyer et al. 2007:46)

“The plant surface is by default flat, and development away from this default is thought to have some function of evolutionary advantage. Although the functions of many plant epidermal cells have been described, the function of conical epidermal cells, a defining feature of petals in the majority of insect-pollinated flowers, has not. The location and frequency of conical cells have led to speculation that they play a role in attracting animal pollinators. Snapdragon (Antirrhinum) mutants lacking conical cells have been shown to be discriminated against by foraging bumblebees. Here we investigated the extent to which a difference in petal surface structure influences pollinator behavior through touch-based discrimination…We show that foraging bumblebees are able to discriminate between different surfaces via tactile cues alone. We find that bumblebees use color cues to discriminate against flowers that lack conical cells—but only when flower surfaces are presented at steep angles, making them difficult to manipulate. This facilitation of physical handling is a likely explanation for the prevalence of conical epidermal petal cells in most flowering plants.” (Whitney et al. 2009:948)