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A group of ancient carnivorous plants have given up on catching scary critters and instead feed on animal droppings. And it turns out these living toilets are getting more nutrients from their new diet than their insect-eating cousins, according to a new study.
Genus tropical pitcher plants Nepenthe are carnivorous plants with large, fluid-filled tubes which they use to trap a wide range of prey, including insects such as antsand arachnids like spiders and scorpions, as well as sometimes larger creatures like frogs or small rodents. The animal feed of plants provides them with additional nutrients, mainly nitrogen, as well as phosphorus and carbon – which helps supplement their growth in nutrient-poor soils.
But a small group of pitcher plants living on the Malaysian island of Borneo have taken things to the next level by developing a taste for animal droppings. This dietary change was first discovered in 2009, when a study published in the journal Biology Letters (opens in a new tab) revealed that mountain pitcher plants (Nepenthes lowii) frequently ate feces left behind by tree shrews (tupaia montana). Later studies found more of these plants, which can also feed on the droppings of rodents, birds and bats. However, until now, no one had tested the nutritional value of their poop-based diet against the insect-rich diets of other pitcher plants.
In a study published on October 28, 2022 in the journal Annals of Botany (opens in a new tab)the researchers compared tissue samples from six species and four hybrids of poop-eating pitchers from the mountains of Borneo with closely related carnivorous species that live at lower elevations.
“We found that nitrogen uptake is more than twice as high in species that take up mammalian feces than in others. Nepenthe“, co-author of the study alastair robinson (opens in a new tab)a botanist from the Royal Botanic Gardens Victoria in Australia, said in a statement (opens in a new tab) published on January 20. Bird droppings provided plants with slightly less nitrogen, but were still more nutritious than a carnivorous diet, he added.
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Carnivorous pitcher plants use fragrant nectar to attract potential prey, which then fall into the tube traps after sliding on smooth plant surfaces. The poop-eating versions also attract animals with their sweet syrups, but instead of fooling their targets, these plants allow animals to feed on the nectar. As the animals take time to consume their sugary snack, they often defecate directly into the pitcher tubes.
The evolution toilet traps was likely triggered because there are fewer insects at higher elevations, the researchers wrote in the paper.
“Insect prey is rare on tropical peaks above 2,200 meters [7,218 feet]so these plants maximize nutrient yields by collecting and conserving fewer higher-value nitrogen sources,” such as animal feces, Robinson said.
The results show that the higher a pitcher plant is in the mountain, the more selective and resourceful it has to be with its diet to get the nutrients it needs, the team wrote.