Formulating a clever strategy doesn't require a brain, proves a new study on carnivorous pitcher plants, which vary their bug-trapping techniques in order to obtain the most food.
The discovery, published in the Proceedings of the Royal Society B, demonstrates that evolved strategies can at times be just as effective as thinking through problems in response to certain challenges.
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The findings also solve a long-standing mystery about tropical pitcher plants that use slippery pitfall traps to capture insects.
"The plant's key trapping surface is extremely slippery when wet, but not when dry," explained project leader Ulrike Bauer of Bristol University's School of Biological Sciences. "For up to eight hours during dry days, these traps are ‘switched off' and do not capture any of their insect visitors. At first sight, this is puzzling because natural selection should favor traps that catch as many insects as possible."
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Bauer and colleagues began the study by surveying wild carnivorous pitcher plants in Borneo. This work revealed that the traps sporadically capture large numbers of ants in batches from the same species.
The researchers next conducted experiments in which they artificially kept the trapping surfaces wet all the time. They found that wetted plants no longer captured large batches of ants.
"Ants are social insects," Bauer said, explaining that individual ‘scout' ants search their surroundings for profitable food sources. When they find a pitcher trap full of sweet nectar, they go back to the colony and recruit many more ant workers.
"However," Bauer added, "a trap that is super-slippery all the time will capture most of these scout ants and cut off its own prey supply."
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The plants' ant recruitment therefore was impeded when the traps were continually kept wet.
To avoid the problem, the plants have evolved the on and off strategy.
"By ‘switching off' their traps for part of the day, pitcher plants ensure that scout ants can return safely to the colony and recruit nest-mates to the trap," Bauer said. "Later, when the pitcher becomes wet, these followers get caught in one sweep."
"What looks like a disadvantage at first sight, turns out to be a clever strategy to exploit the recruitment behavior of social insects."