Bees fooled by mimicry help pollinate sun orchids, driving fruit production.
Deceptive sun orchids are known to mimic nearby flowering plants, displaying showy anthers to lure bees. Now, researchers report that fruit production in sun orchids plummeted up to 71% when false anthers were removed or otherwise occluded. These findings conclusively show that false anthers offer sun orchids immense adaptive advantages.
Some flowering plants make bees work for their food, shaking loose pollen only when the pollinators buzz and vibrate floral anthers. Found in Australia, sun orchids use structures called false anthers that mimic those of competing flowering plants. While this kind of mimicry is especially common, the importance of false anthers for pollination success in sun orchids has not been clearly established.
“True buzz-pollination mimicry should imply that a buzzing behaviour is critical for sun orchid pollination success but, to our knowledge, this has not yet been documented in any deceptive species,” write Daniela Scaccabarozzi and Nina Sletvold, researchers at Uppsala University, Sweden, and co-authors on the study.
Scaccabarozzi and Sletvold identified bees that appeared to pollinate both sun orchids and plants that were the models for the mimicry. Through the lens of bee visual perception, they identified similarities in the form and colour of the sun orchids and the model plants: the floral colours on model plants matched the sun orchids’ colours near perfectly. “Visiting bees attempted to buzz and manipulate the false anther, with a behaviour similar to that observed on model plants,” state the researchers.
The researchers wanted to see if false anthers afforded the sun orchids any material advantages: How would fruit production, an indicator of successful pollination, change if false anthers were cut off or painted over? The team found that painting or removing the false anthers in sun orchids significantly affected fruit production, resulting in a 51% to 71% drop, depending on the specific conditions. “While bees are likely to be attracted to large floral displays from a distance, false anthers may be an important signal in proximity to the flowers,” write the researchers. “The colour contrast between the anther and petal could direct pollinators to the centre of the flower and function as a ‘floral guide’.”
Moreover, even the abundant presence of model plants did not impact fruit production in sun orchids. “Our insect observations revealed that most bees landed directly on the column containing the false anther,” the researchers add, “suggesting that bees mistake orchids for pollen-rewarding plants during their approach.”
Reference: Daniela Scaccabarozzi et al., Do sun orchids mimic buzz-pollinated plants? An experimental test of the adaptive significance of false anthers, Functional Ecology (2025). DOI: https://doi.org/10.1111/1365-2435.70129
Featured image: “Thelymitra graminea – Shy Sun Orchid” by Jean and Fred Hort via Flickr, CC BY 2.0