Many plant species, and particularly those that produce flowers, depend on or benefit from animals to transport pollen from male to female structures. They have therefore evolved to offer rewards such as nectar and produce a variety of signals to attract visitors. Their main strategies are described below:
- Colours: are one of the most important signals in attracting pollinators. In addition to the shades we perceive, insects can also perceive, in general, colours with a wavelength between 300 and 400 nm. On the other hand, it is believed that the contrast of colours in flowers, for example between the colours of the petals and those of the anthers, can be as important a signal as the colours of the flower itself.
- Odours: Volatile compounds act as both short- and long-distance attraction signals, making it easier to locate flowers in low light conditions or when specialised pollinators are looking for particular species. Many plants emit scents that deceive pollinators in order to attract them without offering a reward in return, such as plants that emit scents that simulate food sources they do not possess. Other more curious cases are plants that emit scents of faeces or decaying matter to attract flies and beetles in search of food or a place to lay their eggs. Other species mimic the pheromones of pollinator prey or female insects to attract males who, in trying to mate with the flower, end up pollinating it.
- Shape and size: the shape of the flower influences the handling of pollinators and the way they deposit pollen. In addition, the shape affects the electrostatic properties of flowers, which tend to be negatively charged to aid pollen transfer to positively charged insects. In terms of size, small flowers are accessible to smaller pollinators, while larger flowers are more suitable for large-bodied insects and, in some cases, provide greater foraging efficiency.
- Texture: The petals of insect-pollinated flowers have conical cells that add texture to their surface. These cells are thought to facilitate the insects' grip on the flower. In addition, it has been observed that bumblebees can differentiate, by touch, the texture associated with these cells and associate it with the presence or absence of a reward.
- Temperature: it is believed that the warmth of heat-retaining or heat-generating flowers may be attractive to some insects. In addition, it has been shown that patterns of thermal variation in flowers can guide bees more efficiently to food.
- Humidity: the intensity and pattern of humidity around a flower also varies between species. It has been observed that some pollinators such as moths and bumblebees prefer flowers with high humidity. This preference is probably due to the fact that humidity is usually generated by the evaporation of nectar and would indicate their presence.
- Acoustic signals: some plants pollinated by bats, such as Marcgravia evenia, have structures that reflect the acoustic emissions of these animals and cause them to be attracted to them.
As if these signals were not enough, some flowers also change colour after being pollinated, directing pollinators to flowers that have not yet been visited and therefore offer greater food rewards.
The complexity of communication between plants and pollinators reflects the importance of this relationship for the efficient reproduction of a large number of plant species.
References
Balamurali, G. S. et al. (2015). Senses and signals: evolution of floral signals, pollinator sensory systems and the structure of plant-pollinator interactions. Current Science, 1852-1861.
Rands, S. A. et al. (2023). Multimodal floral recognition by bumblebees. Current Opinion in Insect Science, 59, 101086.
Ruxton, G. D., & Schaefer, H. M. (2016). Floral colour change as a potential signal to pollinators. Current Opinion in Plant Biology, 32, 96-100.
Valenta, K et al. (2017). Plant attractants: integrating insights from pollination and seed dispersal ecology. Evolutionary Ecology, 31, 249-267.
Whitney, H. M. et al. (2009). Conical epidermal cells allow bees to grip flowers and increase foraging efficiency. Current Biology, 19(11), 948-953.
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