Nepenthes Lowii - Carnivory

Carnivory

Nepenthes lowii is known to catch very few prey items compared to other Nepenthes. Preliminary observations suggest that this particular species may have moved away from a solely (or even primarily) carnivorous nature and be adapted to "catching" the droppings of birds and tree shrews feeding at its nectaries.

The upper pitchers of N. lowii are unusual in that they have a reflexed lid, which exposes numerous bristles on its underside. A white substance often accumulates amongst these bristles, the identity of which has been the subject of some debate. In the 1960s, J. Harrison assumed that these white beads were snail eggs. E. J. H. Corner, who led the 1961 and 1964 Royal Society Expeditions to Mount Kinabalu, wrote the following:

a ringing gonging which we traced to tupaias scampering over the pitchers of N. lowii and banging the old empty and resonant pitchers together. The late Professor J. Harrison of Singapore discovered that a snail laid its eggs in the hairs under the lid and that the tupaias came to eat them.

However, observations of cultivated N. lowii by Peter D'Amato and Cliff Dodd showed that these white beads were of the plant's own production. The substance has been described as having a sugary taste and "a slightly disagreeable odour". It is unknown why lower pitchers of N. lowii, which are otherwise typical of the genus, also have bristles and produce these white secretions. Charles Clarke suggested that by providing a reward near the ground, the lower pitchers may serve to guide animals towards the upper pitchers.

Clarke carried out a series of field observations relating to N. lowii carnivory. At five of seven sites studied, N. lowii pitchers were found to contain significant amounts of animal excrement. A 2009 study found that mature plants derived 57–100% of their foliar nitrogen from tree shrew droppings. Another study published the following year showed that the shape and size of the pitcher orifice exactly match the dimensions of a typical tree shrew (Tupaia montana). A similar adaptation was found in N. macrophylla and N. rajah, and is also likely to be present in N. ephippiata. In all three of these species (N. ephippiata has not been investigated), the colour of the lower lid surface corresponds to T. montana visual sensitivity maxima in the green and blue wavebands, making it stand out against adjacent parts of the pitcher.

Nepenthes lowii is not the first Nepenthes species for which this has been proposed; as early as 1989 it was suggested that N. pervillei, a species from the Seychelles, benefits from bird excrement and may be moving away from carnivory. However, no comprehensive studies have been conducted into the carnivory of N. pervillei and this hypothesis has yet to be tested experimentally.