D’em shrews have shat in me again.
Botanist Dr. Charles Clarke (Monash University, based at Monash’s Selangor campus) has published two research papers showing that the pitchers of mature pitcher plant Nepenthes lowii are opportunistic toilets rather than predatory traps.
Carnivorous pitcher plants typically have waxy interiors and other devices in their pitchers and narrow entrances to traps ants or other insects.
Insects are rare in the mountainous habitat of some pitcher plants, like Nepenthes lowii from Borneo and Sarawak. The carnivorous features typical of other pitcher plants are absent in mature Nepenthes lowii and the entrances to the pitchers are broad and open. (Juvenile plants have pitchers growing from ground level that are more typical of the carnivorous species and trap insects. It is the mature plants with their aerial pitchers that were studied.)
While Dr. Clarke had previously reported not observing rodents or invertebrates (insects) trapped in these plants’ pitchers, but observing animal droppings, suggesting an association with animals rather than insects.
In addition to the pitchers, these plants grow a ’lid,’ with glands that exude nectar.
Dr. Clarke’s research showed that these lids where the right size and geometry so that if a shrew were feeding on the nectar, it’s butt would be appropriately placed to defecate into the pitcher.
They tested this hypothesis and that it would provide a nitrogen source for the plants.
Field work in the mountains of Sarawak during 2008 showed that insect captures were rare, but the plants were visited by tree shrews (Tupaia montana), who would feed on the nectar and defecate into the pitchers. The shrews also scent mark the lids.
The lids are robust, able to carry the weight of the animals and the shape of the lid favours feeding in the appropriate orientation.
Using 15N isotope measurements from collected plants samples, they estimated that the plants got 57-100% of their nitrogen from the shrews, with the balance probably from the soil.
This indicates that a mutual benefit has evolved, where the plant offers nectar in exchange for nitrogen (and other minerals).
In more recent work, the group have confirmed that the geometry of these plants is adapted to match the body size of shrews by comparing several species of pitcher plants and the contents of the pitchers. They report that droppings were only found in pitchers with large openings with a lid placed at right angles to the opening, and with nectar glands the length of a tree shrew’s body away from the opening.
Carnivorous plants have acquired a faecal-collecting cousin, with the plant providing a tree-shrew feeding toilet that collects the droppings as a source of nitrogen.
This is an older story, which has already done the circuit, but not seeing any local take on it, I couldn’t help giving it another whirl… Hat tip to Benny Bleiman at Zooillogix for bringing this story to my attention.
When I was a kid I read way too much Gerald Durrell and imagined myself in places like the mountains of Sawarak. I’m envious that these guys have an excuse to go there, paid!
Chin, L., Moran, J., & Clarke, C. (2010). Trap geometry in three giant montane pitcher plant species from Borneo is a function of tree shrew body size New Phytologist, 186 (2), 461-470 DOI: 10.1111/j.1469-8137.2009.03166.x (Not open access.)
Clarke CM, Bauer U, Lee CC, Tuen AA, Rembold K, & Moran JA (2009). Tree shrew lavatories: a novel nitrogen sequestration strategy in a tropical pitcher plant. Biology letters, 5 (5), 632-5 PMID: 19515656 DOI: 10.1098/rsbl.2009.0311 (Open access)
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