Abstract
Knowing what animals eat is fundamental to our ability to understand and manage biodiversity and ecosystems, but researchers often must rely on indirect methods to infer trophic position and food intake. Using an approach that combines evidence from stable isotope analysis and DNA metabarcoding, we assessed the diet and trophic position of Anthene usamba butterflies, for which there are no known direct observations of larval feeding. An earlier study that analyzed adults rather than caterpillars of A. usamba inferred that this butterfly was aphytophagous, but we found that the larval guts of A. usamba and two known herbivorous lycaenid species contain chloroplast 16S sequences. Moreover, chloroplast barcoding revealed high sequence similarity between chloroplasts found in A. usamba guts and the chloroplasts of the Vachellia drepanolobium trees on which the caterpillars live. Stable isotope analysis provided further evidence that A. usamba caterpillars feed on V. drepanolobium, and the possibilities of strict herbivory versus limited omnivory in this species are discussed. These results highlight the importance of combining multiple approaches and considering ontogeny when using stable isotopes to infer trophic ecology where direct observations are difficult or impossible.
Highlights
Few aspects of an organism’s ecology are more fundamental than its diet
Among the known phytophagous species—Flos apidanus and Azanus natalensis—chloroplast sequences comprised between 3% and 98% of samples’ total libraries, whereas the libraries of entomophagous species—Miletus biggsii and Aloeides pallida—were confirmed to contain no chloroplast sequences (Fig 1)
Plant chloroplast barcodes from the gut extracts of all A. usamba samples were identical and blasted with 100% identity to Vachellia drepanolobium Genbank accession KR738641 (S1 Fig) [43]
Summary
Few aspects of an organism’s ecology are more fundamental than its diet. Trophic interactions directly and indirectly influence species distributions and richness, community composition, population dynamics, ecosystem function, primary productivity, and nutrient cycling [1,2,3]. Despite the importance of trophic interactions for understanding fundamental aspects of biodiversity and ecosystems, basic dietary data for many animals are often incomplete, erroneous, or missing. Assessing an animal’s diet is a non-trivial task: diets can be highly variable between individuals and populations of the same species, they may fluctuate or vary according to seasons and geography, and they are often highly dependent on other community and ecosystem. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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