Scientists have discovered a strange give-and-take relationship between pitcher plants and Borneo bats. Pitcher plants provide a resting place for Borneo bats, while Borneo bats provide nutrition to the pitcher plants.

Pitcher plants are ideal for roosting in bats, providing a cool, parasite-free place, not to mention less competition from other bats. The bats provide nutrition by keeping them well fertilized with their droppings.

In a latest study, Universiti Brunei Darussalam's Ulmar Grafe first discovered bats roosting inside pitcher plants. Along with Michael and Caroline Schöner and Gerald Kerth, senior author of the new study, Grafe looked at the relationship between the plants and bats and found that the pitcher plants are bad at attracting insects, unlike their carnivorous relatives. This led them to find a special feature in the plants' structures that is especially designed to attract their bat partners.

In this study published July 9 in the online Cell Press journal Current Biology, the researchers discover that carnivorous pitcher plants, or Nepenthes hemsleyana, have special structures that reflect the ultrasonic calls of the bats back to them. Through this, the bats can more easily find their way toward the plants in a cluttered forest.

"With these structures, the plants are able to acoustically stand out from their environments so that bats can easily find them," said Ernst-Moritz-Arndt-University of Greifswald in Germany's Michael Schöner. Pitcher plants may be shaped like some of its carnivorous relatives; however, the special acoustic feature is unique to them. Bats do not get confused by the appearance of other plants and can easily distinguish their plant partners.

The team also worked with the University of Erlangen-Nuremberg's Ralph Simon who previously studied the acoustic adaptation of bat-pollinated flowers.

To test the acoustic reflectivity of pitcher plants from different positions and angles, Simon and the team used an artificial biometric bat head emitting and recording ultrasound. They found strong echo reflections from the plants' back walls, which showed that the plant form is an effective reflector.

The bats, in turn, are more responsive to sounds that are echoed back to them. In this case the pitcher plant's acoustic reflectors are just what the bats need to be able to locate their roosting plant partners who need their droppings too.

Photo: Mack Lundy | Flickr