The role of fungal parasites in tri-trophic interactions involving lichens and lichen-feeding snails.
Lichens are hosts for a variety of lichenicolous fungi. By investigating two lichens with specialized parasites, we will test the hypothesis that these parasites reduce lichen fitness by increasing the palatability of their respective hosts. The palatability of Lobarina scrobiculata and Lobaria pulmonaria with or without galls of the lichenicolous fungi, Plectocarpon scrobiculatae and P. lichenum, respectively, were quantified in a feeding-preference experiment with grazing snails (Cepaea hortensis). We repeated the experiment for pairs with or without gall in which the carbon-based secondary compounds (CBSCs) had been reduced nondestructively by acetone rinsing. Lichens with galls had lower concentration of CBSCs than those without, but this contrast disappeared after acetone rinsing. In the lichen high in nitrogen (N) (the cyanolichen L. scrobiculata), the grazing was low, and the snails did not discriminate between specimens with and without Plectocarpon-galls. In L. pulmonaria low in N (green algae as main photobiont), the parasite reduced the lichen C : N ratio and the snails strongly preferred specimens with Plectocarpon-galls, regardless of whether CBSC concentration had been reduced or not. In conclusion, some lichen parasites can indirectly reduce lichen fitness by increasing its palatability and thus the grazing pressure from snails, whereas other parasites do not affect grazing preferences.
Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, PO Box 5003, NO-1432, Ås, Norway.
Johan
0000-0001-5610-4480
J
Asplund
Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, PO Box 5003, NO-1432, Ås, Norway.
Yngvar
Y
Gauslaa
Área de Biodiversidad y Conservación, Universidad Rey Juan Carlos, E-28933, Móstoles, Madrid, Spain.
Sonia
S
Merinero
D000818:Animals; D001203:Ascomycota / Q000502:physiology*; D002244:Carbon / Q000378:metabolism; D005247:Feeding Behavior; D020387:Food Chain; D008011:Lichens / Q000382:microbiology*; D009584:Nitrogen / Q000378:metabolism; D010271:Parasites / Q000502:physiology*; D012908:Snails / Q000382:microbiology*
D002244:Carbon; D009584:Nitrogen
carbon-based secondary compounds (CBSCs); carbon : nitrogen (C : N) ratio; chemical defence; herbivory; lichenicolous fungi; palatability; parasitism; tri-trophic interaction