Elevational gradients affect the production of plant secondary metabolites through changes in both biotic and abiotic conditions. Previous studies have suggested both elevational increases and decreases in host-plant chemical defences. We analysed the correlation of alkaloids and polyphenols with elevation in a community of nine Ficus species along a continuously forested elevational gradient in Papua New Guinea. We sampled 204 insect species feeding on the leaves of these hosts and correlated their community structure to the focal compounds. Additionally, we explored species richness of folivorous mammals along the gradient. When we accounted for Ficus species identity, we found a general elevational increase in flavonoids and alkaloids. Elevational trends in non-flavonol polyphenols were less pronounced or showed non-linear correlations with elevation. Polyphenols responded more strongly to changes in temperature and humidity than alkaloids. The abundance of insect herbivores decreased with elevation, while the species richness of folivorous mammals showed an elevational increase. Insect community structure was affected mainly by alkaloid concentration and diversity. Although our results show an elevational increase in several groups of metabolites, the drivers behind these trends likely differ. Flavonoids may provide figs with protection against abiotic stressors. In contrast, alkaloids affect insect herbivores and may provide protection against mammalian herbivores and pathogens. Concurrent analysis of multiple compound groups alongside ecological data is an important approach for understanding the selective landscape that shapes plant defences.
Bibliographical noteFunding Information:
We thank the staff of the New Guinea Binatang Research Centre in Papua New Guinea, especially Bradley Gewa and Grace Luke, for their assistance and Nicholas Silverson and Julia Englund at the Smithsonian who harvested most of the Lepidoptera for sequencing at the Biodiversity Institute of Ontario, as part of the International Barcode of Life project. MV acknowledges funding from Czech Academy of Sciences, and Programme for Research and Mobility Support of Starting Researchers (MSM200962004), Alexander von Humboldt Foundation and the Federal Ministry for Education and Research (Ref.3.3-CZE-1192673-HFST-P), and Grant Agency of the Czech Republic 20-10543Y. KS acknowledges the ERC grant BABE 805189. FV acknowledges support by the Grant Agency of the University of South Bohemia (GAJU n. 048/2019/P). JPS acknowledges funding from the Academy of Finland (grant no 258992), and the help of Saku Valkamaa, Atte Tuominen, Anne Koivuniemi, and Valtteri Virtanen in the chemical analyses. VN acknowledges the ESF grant 669609 and Grant Agency of the Czech Republic 17-23862S and 19-28126X. STS acknowledges funding from a USB Postdoc project reg.no. CZ.1.07/2.3.00/30.0006 (funded by the European Social Fund and the Czech State Budget) and Grant Agency of the Czech Republic 15-24571S. He also acknowledges departmental support from Harper Adams University. We thank the Papua New Guinea Forest Research Institute, in particular Kipiro Damas, for assistance granting export permits.
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- Folivorous mammals
- New Guinea
- Phenanthroindolizidine alkaloids
PubMed: MeSH publication types
- Journal Article