Honeybees are championed as valuable pollinators, but sometimes they steal pollen without helping the plant that makes it. Now, a study of pollen theft by honeybees from a type of non-flowering plant is shedding light on why the very first flowers may have evolved.
Honeybees鈥� reputation for diligent pollination is mostly well鈥慸eserved, but they aren鈥檛 universally good for all plants. at the Fairy Lake Botanical Garden in Shenzhen, China, and his colleagues have discovered that, in the tropical rainforests on the Chinese island of Hainan, the Asian honeybee (Apis cerana) steals pollen from a聽plant called Gnetum luofuense. The bees keep all the pollen they聽collect from this plant for themselves, to the detriment of the plants that they take it from.
鈥淲e were totally surprised because this phenomenon has never been described before for聽this species,鈥� says Wan.
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G. luofuense is a type of gymnosperm, a group of plants that also includes conifers, ginkgos and cycads. While gymnosperms do produce pollen, they don鈥檛 make flowers or fruits, and most species are pollinated by the wind. Before this study, it wasn鈥檛 known that honeybees visited G. luofuense.
Wan鈥檚 team found that honeybees frequently visited male聽G. luofuense plants at dusk and dawn to collect pollen. But the bees avoided female plants altogether, meaning that they didn鈥檛 facilitate any pollination for this species.
Bees weren鈥檛 the only visitors to聽the G. luofuense flowers 鈥� the team also observed visits from Mecodina cineracea moths, which聽attended both male and female plants, serving as effective pollinators. However, when honeybees were present, the team found that these moths carried 70聽per cent less pollen and the plants produced fewer seeds.
These findings provide a glimpse of the time before flowering plants, known as angiosperms, came to dominate, roughly 90 to 125 million years ago. Before angiosperms, gymnosperms were the dominant type of plant life, but only around 1500 species remain today. In comparison, there are more than 350,000 species of angiosperms.
The emergence of new kinds of pollinators, such as bees around 130 million years ago, probably played a role in the origins and subsequent phenomenal success of flowering plants. Wan鈥檚 team thinks that honeybees could have stolen pollen from now-extinct species of gymnosperms before flowers even existed. This could have disturbed the whole pollination systems of extinct gymnosperms, says Wan.
Although honeybees also steal angiosperm pollen, flowers may have arisen as a way to better control the behaviour of thieving bees. Showy petals and sweet nectar, for example, can help ensure that a bee will visit female, as well as male, plants.
The team鈥檚 study also suggests that pollen theft may be a more common problem for the surviving gymnosperm species than previously thought. Bees have also been observed collecting pollen from wind-pollinated conifers, ginkgos and cycads, but it聽is unknown whether these were pollination visits or acts of larceny.
鈥淚f you ask a person in the public聽to name a pollinator, they聽will think of honeybees,鈥� says聽 at McGill University in Canada. 鈥淎nd honeybees are supercool, but they聽can have this really negative effect on some plants.鈥�
Ecology
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