Jacinta Bowler
Jacinta Bowler is a science journalist at Cosmos.
They were published in the Best Australian Science Writing 2023.
High up in the tropical peaks of Borneo, pitcher plants need all the help they can get when it comes to nutrients.
An international team of researchers has discovered eating the poo of mammals in the area is an effective way for some species of tropical pitcher plants (genus Nepenthes)to be able to up their nitrogen – and therefore nutrient intake.
“A handful of Nepenthes species have evolved away from carnivory towards a diet of animal scats,” said one of the researchers, Dr Alastair Robinson, a botanist from the Royal Botanic Gardens Victoria.
“We found that nitrogen capture is more than two times greater in species that capture mammal droppings than in other Nepenthes. Insect prey is scarce on tropical peaks above 2200 metres, so these plants maximise nutritional returns by collecting and retaining fewer, higher-value nitrogen sources like tree-shrew droppings.”
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Carnivorous plants normally live in areas where soil is thin or poor in nutrients, and they’ve adapted to trapping and digesting insects and other tiny animals for their food. But with true ‘waste not want not’ energy, a few species of tropical pitcher plants – usually those that live in high tropical peaks – have adapted to use scat as a good way to get nutrients.
The fact that these pitcher plants were digesting scat was first discovered back in 2009 with the mountain tree shrew. The shrews were feeding on goop produced by the pitcher lids, and then ejecting their waste into the toilet-like ‘bowls’ of the plant below.
Later studies also discovered a similar behaviour by summit rats, woolly bats, and a bird species called the mountain blackeye.
But just how effective this strategy actually was for gaining extra nutrients was unknown until this new paper.
The researchers in this new study looked at how much nitrogen (15N) and carbon (13C) isotopes were in tissue samples of 10 pitcher plants. They also compared species that ate insects compared with species specialised to collect mammal scat and tested co-occurring non-carnivorous plants as reference controls.
“All Nepenthes examined, except N. edwardsiana, were significantly enriched in 15N compared to co-occurring non-carnivorous plants, and 15N enrichment was more than two-fold higher in species with adaptations for the collection of mammal excreta compared with other Nepenthes,” the researchers write in their paper.
“The collection of mammal faeces clearly represents a highly effective strategy for heterotrophic nitrogen gain in Nepenthes.” The research has been published in Annals of Botany.