In Borneo, carnivorous plants known as pitcher plants have evolved special structures that can reflect the ultrasonic call of bats back to the flying mammals to attract them to a symbiotic relationship.
The relationship provides the bats with a cool spot to roost and rest, free from parasites and away from other competing bats. The pitcher plants, in return, receive welcome fertilizer in the form of bat droppings, researchers explain.
The pitcher plants' special bat-attracting evolutionary adaptation makes them easier for the bats to locate in the crowded vegetation of a tropical forest.
"With these structures, the plants are able to acoustically stand out from their environments so that bats can easily find them," says Michael Schöner from Ernst-Moritz-Arndt University of Greifswald in Germany. "Moreover, the bats are clearly able to distinguish their plant partner from other plants that are similar in shape but lack the conspicuous reflector."
Researchers began seeking answers to the peculiar bond between the plants and bats after the first observations of the bats' habit of roosting inside the pitcher plants.
After determining the benefit to each — a secure roosting spot for the bats and nitrogen-rich fertilizer for the plants — the researchers questioned how the species, both somewhat rare and living in a crowded environment, were managing to find each other.
Other plants have been found that use dish-shaped leaves or petals to reflect bat calls and advertise their presence, although it's for a different reason: they've become dependent on nectar-feeding bats to help pollinate them.
The pitcher plant, Nepenthes hemsleyana, isn't related to those nectar-producing plants but has apparently evolved a similar bat-attracting capability for its own purposes — a supply of nitrogen-rich bat guano.
The finding may explain how the pitcher plants survive, since they have been found to be very poor at catching insects when compared with some of their other carnivorous relatives, the researchers say in their study published in Current Biology.
The mutualistic relationship between the pitcher plant and the bats is one more example of the way in which nature, through evolution, can solve problems, the researchers say.
"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," says Schöner. "It is even more astonishing that in the case of N. hemsleyana the system is taking a new turn."