Nepenthes are some of the most recognizable carnivorous plants on the planet, capturing and digesting organic material in their modified leaves to acquire nitrogen and valuable nutrients that are naturally scarce in their habitats. According to new research, some Nepenthes species are capturing more nitrogen, and therefore nutrients, from mammal droppings as compared to those that capture insects.
Nepenthes species sampled in Malaysian Borneo during the study: (A) Nepenthes burbidgeae, (B) Nepenthes edwardsiana, (C) Nepenthes lowii, (D) Nepenthes macrophylla, (E) Nepenthes rajah and (F) Nepenthes villosa. Note the presence of mammal droppings in (D) and (E). Image credit: A. van der Ent / A. Robinson.
“Nepenthes are terrestrial or epiphytic vines or subscandent shrubs that produce a characteristic leaf structure comprising a leaf-like phyllodium (modified leaf base) from the apex of which a tendril emerges, giving rise to an epiascidiate (tubular, with the abaxial surface on the inside) lamina or pitcher,” said Curtin University botanist Adam Cross and his colleagues.
“These evolved primarily as the means of attracting, capturing and digesting prey, and occur in the form of so-called ‘lower pitchers’ and ‘upper pitchers’ specialized towards the capture of crawling and flying insects, respectively.”
“Pitcher shape, size and color are highly variable among species of Nepenthes, but most species produce pitchers with an overhanging lid, a more or less cylindrical peristome surrounding the pitcher mouth (sometimes flattened, markedly flanged or toothed), and interior walls comprising a glandular zone sometimes surmounted by an upper waxy zone.”
“Extrafloral nectaries on the tendril, outer pitcher wall, underside of the lid and between each pair of teeth on the inner edge of the peristome act as prey attractants.”
“Prey fall into the pitcher upon encountering anti-adhesive ‘slippery’ surfaces on the peristome or on the pitcher wall.”
“These surfaces often comprise epicuticular wax crystals which detach and adhere to the tarsi and claws of invertebrate prey or comprise microstructures such as trichomes, lunate cells and digestive glands that impair grip.”
“Captured animals drown in an enzyme cocktail fluid that also facilitates the decomposition of, and nutrient-acquisition from, prey.”
In the study, the researchers studied isotope enrichment in Nepenthes tissue samples to compare the levels of externally acquired nitrogen and carbon present.
They compared the species that capture invertebrates with those that are specialized for the collection of mammal droppings, also testing 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.
“A handful of Nepenthes species have evolved away from carnivory towards a diet of animal droppings,” said Dr. Alastair Robinson, a botanist at 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 2,200 m, so these plants maximize nutritional returns by collecting and retaining fewer, higher-value nitrogen sources like tree-shrew droppings.”
The findings were published in the Annals of Botany.
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Adam T. Cross et al. 2022. Capture of mammal excreta by Nepenthes is an effective heterotrophic nutrition strategy. Annals of Botany 130 (7): 927-938; doi: 10.1093/aob/mcac134
Source : Breaking Science News