Science on the Edge

The Raffles' pitcher plant (Nepenthes rafflesiana) is a strange plant. For years it baffled scientists by its apparent incompetence at catching insects, the primary activity by which the carnivorous pitcher plants obtain their food. Recent research however is pointing to a different source of sustenance...bat guano! This particular species differs from its relatives in that it possesses a long and narrow pitcher, with no apparent scent or pattern for attracting insects. Normally, pitcher plants employ enticing aromas, ultraviolet decorations, and delicious nectar to attract insects which promptly slip into the small leaflike cups (the pitchers) and drown in a pool of digestive fluids allowing the plant to obtain otherwise absent nutrients.

On a research expedition in the jungles of Borneo, lead scientist Ulmar Grafe and some students came across a bat roosting in the pitcher of one of these plants. The dismissed it as happenstance until Grafe read a paper describing the apparent lack of insect-killing ability of this particular plant. Over a period of 7 weeks, Grafe and his team made countless pitcher plant patrols and discovered that nearly 25% of the plants they found had bats roosting in them, more specifically Hardwicke's wooly bats (Kerivoula hardwickii). These bats are usually less than 4 cm long, making them the perfect size for the pitchers of these plants.




To investigate further, the team glued tiny transmitters to the backs of 17 bats and tracked where they slept each night. They found that the bats all slept in Raffles' pitcher plant cups, often times with mother and either a son or daughter, if present. Looking at the size and shape of the pitcher, one or two bats are capable of fitting perfectly, just above the digestive fluid. Interestingly, the bats wedge themselves in head-first, although they undoubtedly make the obligatory flip to the right-way-up before going to the bathroom.

Analysis of the plants showed that leaves adjacent to the pitchers in which bats were known to have slept had 13% greater nitrogen content than those adjacent to pitchers without bat occupancy. The researchers tested leaf blades for a nitrogen isotope found in the carnivorous bats, and therefore their poop, and discovered that nearly 1/3 of the nitrogen in those leaves came from the bat guano. Researchers in the field seem excited about the findings and are extremely interested in finding out if this is a case of coevolution or if more pairings occur.

I know that I will be sure to keep my eye out for these awesome plants when I am trekking through the jungles of Borneo next spring!