Reassessing protocarnivory – how hungry are triggerplants?
Francis J. Nge
A B C and Hans Lambers A
A School of Biological Sciences, University of Western Australia, 35 Stirling Highway, Crawley (Perth), WA 6009, Australia.
B School of Biological Sciences, Faculty of Science, The University of Adelaide, Adelaide, SA 5005, Australia.
C Corresponding author. Email: francis.nge@adelaide.edu.au
Australian Journal of Botany 66(4) 325-330 https://doi.org/10.1071/BT18059
Submitted: 20 March 2018 Accepted: 7 June 2018 Published: 9 July 2018
Abstract
Stylidium species (triggerplants) are claimed to be protocarnivorous based on the presence of glandular hairs, observations of trapped small organisms, and induction of proteinase activity. However, these traits might serve alternative functions. We aimed to re-assess and quantify the degree of carnivory for Stylidium species in an ecological context, by comparing the natural abundance (δ15N) of Stylidium species with co-occurring carnivorous (Drosera species) and non-carnivorous plants in their natural habitats. We hypothesised that the δ15N signature of Stylidium species would more closely match co-occurring carnivorous plant species than their non-carnivorous counterparts if they rely on captured organisms as a nutrient source, since there is an increase in fractionation by 3–5 ‰ per trophic level. Our results show that the Stylidium species sampled had δ15N signatures that matched more closely with co-occurring non-carnivorous plants than with carnivorous Drosera species. This does not support the claim that they rely on captured organisms as a nitrogen source, or the source is negligible. Other studies have shown that protocarnivorous species have a δ15N signature that is more similar to that of co-occurring carnivorous than that of non-carnivorous species. Therefore, our findings question the protocarnivory status of Stylidium species.
Additional keywords: carnivorous plants, Drosera, insectivorous plants, protocarnivorous plants, stable nitrogen isotopes, Stylidium, Stylidiaceae.
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