A mammal poo-based diet could be more nutritious than you think

Could animal droppings be more nutritious than insects? Apparently so, according to some carnivorous plants in a recent study.

Botanist Dr Alastair Robinson, Manager Biodiversity Services at Royal Botanic Gardens Victoria, and colleagues in Western Australia, Queensland, Malaysia, and Germany have showcased in new work  that some tropical carnivorous plants called Nepenthes are getting more of their required daily nitrogen, and therefore nutrients, from mammal droppings instead of insects.

A new and supposedly improved diet of droppings

“A handful of Nepenthes species have evolved away from carnivory towards a diet of animal scats,” said Robinson in a press release accompanying the new study.

“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 meters, so these plants maximize nutritional returns by collecting and retaining fewer, higher-value nitrogen sources like tree-shrew droppings,” he added.

Robinson’s team examined isotope enrichment in Nepenthes tissue samples to compare the levels of externally acquired nitrogen and carbon present. In their revolutionary work, they compared the species that capture insects with those that focus on the collection of mammal excrements.

To make sure their results were not skewed, they also tested co-occurring non-carnivorous plants as reference controls.

“They found that the heavier 15N isotope of nitrogen was significantly enriched in all Nepenthes tested as compared to non-carnivorous plants nearby, but that 15N levels were even greater in those Nepenthes specialized to capture mammal droppings,” stated the press release.

Nepenthes are some of the most recognisable carnivorous plants on Earth. They are known for their unique ability to capture and digest organic material in their modified leaves to acquire nitrogen and valuable nutrients that are naturally scarce in their habitats. There are around 160 known and named Nepenthes species.

Magnetic fields generated

Ground-breaking research surfaced in February 2021 on another carnivorous plant, the Venus flytrap (Dionaea muscipula). It had been long known that the species used electrical signals to close its leaf lobes to capture its prey.

An interdisciplinary team of scientists from Johannes Gutenberg University Mainz (JGU), the Helmholtz Institute Mainz (HIM), the Biocenter of Julius-Maximilians-Universität of Würzburg (JMU), and the Physikalisch-Technisch Bundesanstalt (PTB) in Berlin then proved that these electrical signals generate magnetic fields.

"You could say the investigation is a little like performing an MRI scan in humans," said physicist Anne Fabricant, a doctoral candidate in Professor Dmitry Budker's research group at JGU and HIM (at the time). "The problem is that the magnetic signals in plants are very weak, which explains why it was extremely difficult to measure them with the help of older technologies."

The revelation, just like this latest find, transformed how we looked at the plants. The new research is published in the Annals of Botany Journal.

Abstract:

While isotopic enrichment of nitrogen (15N) and carbon (13C) is often used to determine whether carnivorous plant species capture and assimilate nutrients from supplemental sources such as invertebrate prey or mammal excreta (heterotrophic nutrition), little is known about how successful the different strategies deployed by carnivorous plants are at obtaining supplemental nutrition. The collection of mammalian faeces by Nepenthes (tropical pitcher plants) is the result of a highly specialized biological mutualism that results in heterotrophic nitrogen gain; however, it remains unknown how effective this strategy is in comparison to Nepenthes species not known to collect mammalian faeces.