The study, published in the journal Current Biology, shows that carnivorous plants have reflective structures that are acoustically attractive for mutualistic bats. It’s yet another fascinating example of how nature and evolution solve problems.

Mutualisms between plants and animals shape the world’s ecosystems. In such interactions, achieving contact with the partner species is critical. Plants regularly advertise themselves with signals that specifically appeal to the partner’s preferences.

On the island of Borneo, carnivorous pitcher plants have developed an intriguing relationship with bats.

The plants offer the bats a relatively cool place to roost, free of parasites and competition from other bats. In return, the bats keep the plants well fertilized with their droppings.

Now, Dr Michael Schöner from the Ernst-Moritz-Arndt-University of Greifswald and co-authors show that the plants rely on special structures to reflect the bats’ ultrasonic calls back to them. That adaptation of the plants makes it easier for bats to find their plant partners in the cluttered forest.

“With these structures, the plants are able to acoustically stand out from their environments so that bats can easily find them. Moreover, the bats are clearly able to distinguish their plant partner from other plants that are similar in shape but lack the conspicuous reflector,” Dr Schöner explained.

In their study, Dr Schöner and his colleagues wondered how pitcher plants Nepenthes hemsleyana and Hardwicke’s woolly bats (Kerivoula hardwickii) find each other.

In Borneo, the scientists used an artificial biomimetic bat head that emits and records ultrasounds to test the pitchers’ acoustic reflectivity from different positions and angles. Those experiments uncovered a strong echo reflection from the pitchers’ back walls, where the plant form works perfectly as an effective reflector.

Behavioral experiments showed that the bats respond to those sounds echoed back to them from the plants.

Bats were better at finding partially hidden pitcher plants when their reflectors were intact than when the reflector had been reduced. The bats also chose pitcher plants more often as the best places to roost when the reflector had not been reduced.

“Carnivorous plants in general have already solved the problem of nutrient deficiency in a very unusual way by reversing the normal system of animals feeding on plants,” Dr Schöner said.

“It is even more astonishing that in the case of Nepenthes hemsleyana the system is taking a new turn.”

“While Nepenthes hemsleyana reduced many insect-attracting traits, it obviously exhibits some traits that are highly attractive for a species that provides the plants with nutrients without being digested by the plant itself,” he said.

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Michael G. Schöner et al. Bats Are Acoustically Attracted to Mutualistic Carnivorous Plants. Current Biology, published online July 09, 2015; doi: 10.1016/j.cub.2015.05.054