Lichen specific metabolites (LSMs) have interesting biological activities and quantitative
variations may be present intraspecifically. For example, variations in medullary
fumarprotocetraric acid (FA) and cortical usnic acid (UA) were observed in the lichen
Cladonia foliacea , but the mechanism of variation is not well understood. The current
study aimed to characterise the quantitative variation of FA and UA and to investigate
the association between lichen metabolite content and ecological / biological variables.
Fungal and algal trees were constructed using fungal (nrITS, RPB2) and algal (nrITS)
loci, respectively. Using a chiral chromatographic method, the contents of (-)-UA
were determined in 29 C. foliacea specimens and range from 6.88 to 34.27 mg/g dry
wt. The FA contents were lower and varied from 1.44 to 9.87 mg/g dry wt. Although
the fungal tree showed two well resolved clades, no significant differences of UA
or FA contents were found between the two fungal clades. However, a significantly
higher UA/FA ratio as well as a unique habitat were found to be associated with specimens
which contained the alga Asterochloris lobophora than those specimens associated other
Asterochloris algae. Taking all predictive variables into account (i.e. substrate
type, elevation, collection season, photobiont identity), the multivariate data analysis
indicated that photobiont identity explained most of the variance of LSM contents
in C. foliacea . Thus future LSM biosynthetic studies should take the photobiont into
consideration when dealing with intraspecific quantitative variation.
