Echolocating bats can more easily find and pollinate long-stemmed flowers that stand out from the surrounding foliage, which may be why this floral trait evolved.
Some flowers may have evolved long stems to make it easier for echolocating bats to find them.
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| A tailed tailless bat drinking nectar from a flower Nathan Muchhala |
Like insects and hummingbirds, bats that feed on nectar are important pollinators for hundreds of species of plant, including mango and agave. Many of these plants have flowers that share distinctive characteristics to appeal to bats such as opening at night or giving off a musty odour. These flowers also tend to have long stems that hang down from branches or extend from trunks.
Nathan Muchhala at the University of Missouri–St. Louis and his colleagues tested how long it took 10 wild bats to find flowers with different stem lengths. Because these bats – amusingly named tailed tailless bats (Anoura caudifer) – have limited vision, they navigate by echolocation, emitting high-frequency sound waves that bounce back to them.
The researchers set up net enclosures at night within the cloud forest in Colombia where they captured the wild bats. Then they placed a single bloom from the bellflower plant Burmeistera succulenta on a post within the enclosure, using a wire to vary the length of the stem. In half of the tests, only the flower was attached to the post; in the other half, it was surrounded by foliage.
When the flower was alone, it took the bats the same amount of time to find the bloom whether it had a short or long stem. However, when the flower was surrounded with foliage, as it would be in nature, the bats found the long-stemmed flowers almost twice as fast as the short-stemmed ones, taking around 18 rather than 30 seconds on average.
This is good evidence that long stems are the echolocation equivalent of “becoming bright red to a bat”, says Laura Lagomarsino at Louisiana State University, who wasn’t involved in the work. “They’re sticking themselves out where there’s less auditory static.”
Journal reference
New Phytologist DOI: 10.1111/nph.20075