Abstract
Roccella species constitute interesting models to address questions regarding lichen metabolite diversity across taxonomic, ecological and geographic gradients. Indeed, owing to their wide distribution, their taxonomic diversity and the narrow ecological niche they occupy, Roccella species are good candidates to study the drivers of lichen chemistry. This study focuses on the chemical profiling of five species: R. applanata, R. belangeriana, R. fuciformis, R. montagnei and R. phycopsis. These five species were sampled in a rather narrow longitudinal range (1°51′W to 47°17′E) covering the Eastern Atlantic and Western Indian Ocean areas along an extended latitudinal range (48°49′N to 22°23′S). High Pressure Liquid Chromatography (HPLC) analysis followed by mass spectrometry of 31 Roccella thalli revealed a number of interesting patterns through a multivariate (PCA) analysis, including the first detailed chemical profiles for two species from the Scattered Islands: R. applanata and R. belangeriana. Metabolite segregation amongst all studied Roccella species, including R. montagnei and R. belangeriana, gave some insight into the taxonomy of the latter two species, which we interpret as separate species. An additional analysis focusing on R. montagnei samples revealed chemical differences along both a latitudinal and ecological gradient (from Europa Island to São Tomé and Príncipe). Three mass spectra databases were built to dereplicate the ions, which gave an overview of the factors that could drive quantitative and qualitative metabolite composition in lichens. Additionally, several new Roccella species records are reported for the Scattered Islands, as well as São Tomé and Príncipe.
Highlights
Roccella is a diverse genus of fruticose lichens numbering approximately species [24 according to Tehler et al (2010); according to Aptroot and Schumm (2011)]
The establishment of metabolic profiles of the five Roccella species included in this study (Table 2) improves our knowledge of these species’ chemistry and according to the data contained in RoccellaDB, five compounds were detected for the first time in this genus: 2,4-dihydroxyphthalide (R. phycopsis; French mainland); orcinyl lecanorate (R. phycopsis; French mainland); roccellaric acid (R. montagnei; Grande Glorieuse); cholesta-3,5-dien-7-one (R. belangeriana; Europa Island); and oleic acid (R. belangeriana; Europa Island)
These analyses performed under the same conditions with all specimens allowed us to assess metabolite variation between species with a maximum diversity of compounds reached by R. belangeriana (n = 11), followed by R. montagnei (n = 10), R. phycopsis (n = 9), R. applanata (n = 8) and R. fuciformis (n = 4)
Summary
Roccella is a diverse genus of fruticose lichens numbering approximately species [24 according to Tehler et al (2010); according to Aptroot and Schumm (2011)] This genus, which is mainly coastal and restricted to tropical, subtropical, Mediterranean and hyper-oceanic localities of temperate areas, has long drawn naturalists’ interests as most of its species have large, fruticose thalli (sometimes in abundant populations) and are of economic interest for their tinctorial properties. For these reasons, Roccella was among the first lichen genera to be described (de Lamarck & de Candolle 1805) and it has. Special attention is paid here to assessing chemical diversity (both quantitative and qualitative) of these species along the following gradients: species, individuals, territories and ecology
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