The History of Plants and Pollinators: A Tale of Evolution and Symbiosis
Pollination is the key to sexual reproduction in plants, and it’s a process that has shaped the natural world for millions of years. It happens when pollen from a flower's male anthers is transferred to the female stigmas, allowing fertilization to occur. This enables plants to produce seeds and ensures they will bear full-bodied fruit, which in turn impacts the quantity and quality of our food.
But did you know that over 90% of the plant species on Earth today rely on animals for pollination? Surprisingly, this wasn’t always the case. Early plants depended on wind and water to spread their pollen. However, around 245 to 200 million years ago, the first flowering plants began to emerge, evolving new reproductive adaptations that would change the course of plant evolution forever. These plants developed exposed male stamens to bear pollen and enclosed female carpels to protect ovules, creating an explosive increase in pollination diversity. This evolution brought about the intricate relationships between plants and pollinators we see today.
The Early Days of Pollinators
The earliest pollinators, like beetles, flies, and wasps, were passive in their role. These insects fed on the nectar, pollen, and resins secreted by prehistoric flowers, unintentionally carrying pollen from plant to plant. Over time, plants adapted to these early pollinators by evolving different bloom times, colors, scents, shapes, and rewards that helped attract the right visitors at the right time. This coevolution helped improve reproductive efficiency and formed the foundation for the diverse plant-pollinator relationships we now see across the world.
The Arrival of Honey Bees: A New Kind of Pollinator
About 100 million years ago, a new and more intentional pollinator appeared on the scene—bees! Bees are believed to have evolved from predatory wasps. While adult bees and wasps both consume sugars, their larvae have different dietary needs. Bee larvae (like honey bees) feed on pollen, while wasp larvae are typically carnivorous. This shift to a pollen-based diet led to an evolutionary partnership between bees and flowers. Honey bees became expert pollinators, developing special adaptations such as pollen-collecting hairs to transport pollen efficiently back to the hive.
Unlike specialized pollinators that focus on one type of plant, honey bees are generalists. They can forage on a wide range of plant species, making them incredibly valuable to the health of diverse ecosystems and agriculture alike.
Bright yellow ceanothus pollen on a bee’s pollen basket
How Plants Communicate with Bees
To ensure their survival, plants have developed clever strategies to attract pollinators like honey bees. Flowers use visual cues, scents, and even ultraviolet signals to communicate with bees and guide them toward nectar and pollen.
Color plays a huge role in attracting bees. Flowers change their colors at different stages of development, signaling to bees when they are ready for pollination. Interestingly, bees see the world quite differently from humans. While both bees and humans are trichromatic (meaning we each have three photoreceptors in our eyes), we see different parts of the color spectrum. Humans see red, blue, and green, while bees see ultraviolet, blue, and green. Since bees cannot see red, they’re more attracted to colors like purple, violet, and blue. (For all you beeks out there, here’s a fascinating article explaining bee vision).
Nectar guides are another way flowers communicate with bees. These are contrasting patterns or lines on petals that act as roadmaps, directing bees to the nectar and pollen. While some of these patterns are visible to us, they’re much more pronounced under a bee’s ultraviolet vision.
A flower’s fragrance is also a key attractant, especially for long-distance pollination. Bees are drawn to flowers by their scent, which varies in concentration and intensity depending on the species and environmental conditions. For young bees learning to forage, scent plays an essential role in helping them locate flowers.
Passionflowers have beautiful nectar guides that direct honey bees to their nectar reward
The Nutritional Partnership
In exchange for pollination, flowers provide honey bees with two critical food sources: nectar and pollen. Both are essential for the bees’ survival, particularly when it comes to storing provisions for winter.
Pollen is produced by a flower’s anthers and is a rich source of protein, amino acids, vitamins, minerals, and fats for bees. Worker bees mix pollen with nectar and glandular secretions to create “bee bread,” a fermented, more digestible version of pollen that they feed to their larvae. A variety of pollen sources is crucial for honey bee health, as it ensures a well-balanced diet.
Nectar, on the other hand, is a sugary liquid secreted by plants, providing honey bees with carbohydrates that give them the energy to fly long distances. Honey bees can travel up to 5 miles in search of food, making nectar a crucial fuel source. Once collected, bees dehydrate the nectar from 60-80% water down to 18% or less, transforming it into honey, which is stored in the hive for the colder months. Bees typically need around 100 pounds of honey to survive the winter.
Interestingly, a plant’s nectar secretion can vary dramatically based on factors like humidity, temperature, and time of day. This means that even the same species of plant may produce different nectar qualities depending on its environment.
A Relationship Built on Millions of Years of Evolution
The relationship between plants and pollinators like honey bees has been fine-tuned over millions of years. From their early days as passive pollen carriers, pollinators have become essential players in the life cycle of flowering plants. Today, honey bees are some of the most efficient pollinators in the world, ensuring the survival of countless plant species while feeding their colonies.
This symbiotic relationship continues to shape the natural world, contributing to the biodiversity and food production that sustain life on Earth.