Rajah Pitcher Plant and Tree Shrew

A recently discovered mutualistic relationship exists between 3 species of Nepenthes genus carnivorous pitcher plants and the mountain treeshrew (Tupaia montana). In this blog I will focus specifically on the Rajah Pitcher Plant (Nepenthes rajah) and the mountain treeshrew which are located and endemic to the tropical regions of Borneo (Greenwood et al., 2011).  

These pitchers are distributed in nutrient deficient substrates in which its acquisition of essential nutrients such as nitrogen and phosphorus cannot be sourced via the typically method seen in most species of plants. These three species have shown to dominate the specialized acquisition of nutrients away from the typical arthropod trapping strategies (Moran et al., 2003). Each have developed certain attributes which specifically attract the montane treeshrew in the rather unusual mutualistic relationship in which the treeshrew defecates into the Nepenthes’ pitchers. The treeshrew does this whilst visiting the pitchers to access the delicious secretions from the strategically positioned pitchers lids which is rich in carbohydrates (Greenwood et al., 2011). The Rajah Pitcher has had some interesting studies conducted investigating the pitcher geometry. It was found that the distance from the front of the pitchers digestive organ to the secretionary glands is exactly that of the treeshrews head to body length. The only way for the treeshrew to access the delicious secretions is to orientate its self so its rear is hovering above the pitchers mouth in which it defecates into as a marking of feeding territory (Walker, 2010).

Figure 1. Photographer: Chien Lee (2011) Rajah pitcher plant (Nepenthes rajah) with Mountain Treeshrew (Tupaia montana). 

A study conducted by Greenwood, et at. 2011, indicated that more than one species of mammal visits the pitchers. A small number of mammals visit the N. rajah during daylight and night periods with the treeshrew only visiting in daylight hours whilst a small rat species (Rattus baleunsis) was seen to visit both during nocturnal and diurnal hours. It was found that sugar concentrations of the secretions do not significantly differ in neither day nor night period suggesting that multidirectional resource-based mutualism between a mammal and a carnivorous plant which is the second known example discovered. It was also discovered the N. rajah is the first species of the Nepenthes species to benefit from nocturnal and diurnal mammalian faecal input (Greenwood et al., 2011).

T. montana is also known to display a relatively simply intestinal morphology which results in moderately short digestion tract and passage time which causes the treeshrews to regularly defecate in time periods no longer than one hour which is largely beneficial for N. rajah (Emmons, 2000). The down side to this is that the nutrient extraction within the treeshrew through the intestinal tract is low and causes an increase in nutrient content in the excreted in the scats. This is suggested to be the reason they visit these pitchers so vigorously to supplement their diet and gain the essential nutrients they require (Clarke et al., 2009).

A very interesting relationship exists between these two symbionts with a large amount of room for further scientific investigation to uncover more of the unusual mutualism and the benefits each receive. The below video shows a treeshrew accessing secretions from N. rajah and depositing excrement.

Video with thanks to BBC Earth 

https://www.youtube.com/watch?v=TwL7K_loRjM

References:

CLARKE, C. M., BAUER, U., CH'IEN, C. L., TUEN, A. A., REMBOLD, K. & MORAN, J. A. 2009. Tree shrew lavatories: a novel nitrogen sequestration strategy in a tropical pitcher plant. Biology Letters, 5, 632-635.

EMMONS, L. 2000. Tupai: a field study of Bornean treeshrews, Univ of California Press.

GREENWOOD, M., CLARKE, C., CH'IEN, C. L., GUNSALAM, A. & CLARKE, R. H. 2011. A unique resource mutualism between the giant Bornean pitcher plant, Nepenthes rajah, and members of a small mammal community. PLoS One, 6, e21114.

MORAN, J. A., CLARKE, C. M. & HAWKINS, B. J. 2003. From carnivore to detritivore? Isotopic evidence for leaf litter utilization by the tropical pitcher plant Nepenthes ampullaria. International Journal of Plant Sciences, 164, 635-639.

WALKER, M. 2010 Giant meat – eating plants prefer to eat tree shrew poo. BBC Earth news. Retrieved from http://news.bbc.co.uk/earth/hi/earth_news/newsid_8552000/8552157.stm on 29/05/2015

Figure 1. Chien Lee (2011) Rajah pitcher plant (Nepenthes rajah) with Mountain Treeshrew (Tupaia montana).