Lichen compounds restrain lichen feeding by bank voles (Myodes glareolus)

Some lichen compounds are known to deter feeding by invertebrate herbivores. We attempted to quantify the deterring efficiency of lichen compounds against a generalist vertebrate, the bank vole (Myodes glareolus). In two separate experiments, caged bank voles had the choice to feed on lichens with natural or reduced concentrations of secondary compounds. We rinsed air-dry intact lichens in 100% acetone to remove extracellular compounds non-destructively. In the first experiment, pairs of control and rinsed lichen thalli were hydrated and offered to the bank voles. Because the lichens desiccated fast, we ran a second experiment with pairs of ground control and compound-deficient thalli, each mixed with water to porridge. Eight and six lichen species were tested in the first and second experiment, respectively. In the first, bank voles preferred compound-deficient thalli of Cladonia stellaris and Lobaria pulmonaria, but did not discriminate between the other thallus pairs. This was likely a result of deterring levels of usnic and stictic acid in the control thalli. When lichens were served as porridge, significant preference was found for acetone-rinsed pieces of Cladonia arbuscula, C. rangiferina, Platismatia glauca, and Evernia prunastri. The increased preference was caused mainly by lower consumption of control thalli. Grinding and mixing of thallus structures prevented bank voles from selecting thallus parts with lower concentration of secondary compounds and/or strengthened their deterring capacity. We conclude that some lichen secondary compounds deter feeding by bank voles.