Friday, 26 October 2012

Loo for a Shrew: A Pitcher Plant with a Difference

Frances Cartwright

Most of us will be familiar with the spectacularly evolved insect-eating pitcher plants that are found around the tropics in Malaysia, Indonesia, Borneo and the Philippines. The soil in these areas is generally low in the nutrients necessary to support plant growth, so these plants have evolved to extract nutrients from surprising sources. Typically this involves trapping unsuspecting insects that are lured by nectar to the plant then slip off the rim of the pitcher and tumble into a pool of digestive juices below. Nutrients, released from the breakdown of the catch are absorbed by the plant and used for growth. There are about 140 known species of pitcher plant that trap insects using variations on this theme. They are all members of the plant genus Nepenthes

One member of this family, Nepenthes lowii, uses a strikingly different method to get extra nutrients. The design of the giant, football-sized, pitcher has evolved to be a loo for a tree shrew. The lid of the pitcher is coated in thick sweet nectar that attracts the small mammal. The shrew climbs onto the pitcher to get the sugary treat and whilst indulging, deposits some faeces into the pitcher. Once it is satisfied (and empty!) it goes on its way. The funnel shape of the plant means that the next time it rains, the faeces is washed into the bottom of the pitcher where the nutrients are absorbed by the plant. It is thought that this species of plant gets between 60 and 100% of their nitrogen from tree shrew poo!

It is likely that this mutualistic relationship has been in place for some time because the pitchers are so precisely tailored to the activities of the tree shrew. Unlike the insect-catching pitcher plants that have slippery wax coating the rim of the pitcher, for the shrew’s comfort, the rim of the lowii is wax free to provide the shrew with better grip for eating and stability to protect it from unpleasant spill from within the plant.

Find out more about the science behind this phenomenon, click here.

Check out this video