Monday, July 25, 2011

Another pitcher plant symbiosis

Regular readers might recall my interest in carnivorous plants (see posts on toilets, bacteria, and tiny frogs). If the world was originally created with plants to provide food for immortal animals, how did we end up with plants that actually eat animals? That's a great question that I can't yet answer definitively, but I am becoming more and more intrigued by reports of unusual functions of Nepenthes pitcher plants. I previously noted the report of tree shrews using Nepenthes as toilets, with the plants getting nitrogen from the feces. Normally, pitcher plants get their nitrogen from digesting insects. Recently, there a new report of what appears to be a symbiosis between Nepenthes rafflesiana elongata and Hardwicke's woolly bat (Kervoula hardwickii hardwickii).

According to the report by Grafe et al., the pitchers of Nepenthes rafflesiana elongata are pretty poor at catching insects. They also have an unusually elongated structure, and they don't have the same smell as other Nepenthes rafflesiana varieties. But they do have bats. In their study of these plants in the wild, Grafe et al. repeatedly found bats living inside of the pitchers, perched just above the digestive fluid. They suspected that the plants were gaining nitrogen from the bats' urine or feces, so they measured the nitrogen content of Nepenthes leaves. Sure enough, the plants with bats had significantly higher nitrogen than those without bats.

So that's another example of a Nepenthes pitcher functioning basically as a toilet. Maybe that was the original point?

Grafe et al. 2011. A novel resource-service mutualism between bats and pitcher plants. Biology Letters 7:436-439.

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