Wednesday, March 13, 2013

[Botany / Mutualism • 2011] A Unique Resource Mutualism between the Giant Bornean Pitcher Plant, Nepenthes rajah, and Members of a Small Mammal Community

Rattus baluensis visiting a Nepenthes rajah pitcher at night.
: We found that in addition to Tupaia montana, the summit rat, Rattus baluensis, habitually visits N. rajah pitchers to feed on nectar produced by glands on the pitcher lids. Like T. montanaR. baluensis frequently deposits scats into N. rajah pitchers. Despite an intensive monitoring effort, no other vertebrates were observed to exploit nectar resources nor defecate in pitchers during this study.
photo: Ch'ien Lee


The carnivorous pitcher plant genus Nepenthes grows in nutrient-deficient substrates and produce jug-shaped leaf organs (pitchers) that trap arthropods as a source of N and P. A number of Bornean Nepenthes demonstrate novel nutrient acquisition strategies. Notably, three giant montane species are engaged in a mutualistic association with the mountain treeshrew, Tupaia montana, in which the treeshrew defecates into the pitchers while visiting them to feed on nectar secretions on the pitchers' lids.

Although the basis of this resource mutualism has been elucidated, many aspects are yet to be investigated. We sought to provide insights into the value of the mutualism to each participant. During initial observations we discovered that the summit rat, R. baluensis, also feeds on sugary exudates of N. rajah pitchers and defecates into them, and that this behavior appears to be habitual. The scope of the study was therefore expanded to assess to what degree N. rajah interacts with the small mammal community.

We found that both T. montana and R. baluensis are engaged in a mutualistic interaction with N. rajahT .montana visit pitchers more frequently than R. baluensis, but daily scat deposition rates within pitchers do not differ, suggesting that the mutualistic relationships are of a similar strength. This study is the first to demonstrate that a mutualism exists between a carnivorous plant species and multiple members of a small mammal community. Further, the newly discovered mutualism between R. baluensis and N. rajah represents only the second ever example of a multidirectional resource-based mutualism between a mammal and a carnivorous plant.

Greenwood M, Clarke C, Lee CC, Gunsalam A, Clarke RH. 2011. A Unique Resource Mutualism between the Giant Bornean Pitcher Plant, Nepenthes rajah, and Members of a Small Mammal Community. PLoS ONE. 6(6): e21114. doi:10.1371/journal.pone.0021114

  Rattus baluensis visiting a Nepenthes rajah pitcher at night.: