Large expanses of lichens that cover northern ecosystems form a mosaic of interactions (symbioses) between algae and fungi. The widespread success of these lichens may be attributed to the algal symbiont and fungal secondary metabolites (natural products). Algal sugars produced during photosynthesis are transferred to the fungal partner and used in the synthesis of natural products. These natural products have ecological benefits - such as light screening and antimicrobial activity - that help the lichen survive in its habitat. The same natural products may also have applications in biotechnology. The long-term goal of this research is to understand the functional ecology and evolution of lichen symbionts and their natural products in lichen-dominated habitats. I will investigate ecological patterns in the algal symbiont and fungal polyketide production in 4 lichen species distributed among continental and coastal habitats across Canada. The variation in the natural products of these species will address hypotheses on whether algal symbionts and climate influence their production. Since the alga is essential for the lichen symbiosis, natural products that help protect the alga from adverse conditions should be produced by the lichens in early stages of the symbiosis. Therefore, we will also compare transcriptionally active genes in 2 culture treatments; the fungus growing alone and the fungus and alga interacting together. This comparison will allow us to understand the genes that have been turned on because of the symbiotic interaction and whether any of these genes produce natural products. My research program has already provided a better understanding of the evolutionary and adaptive strategies of lichen symbioses in lichen-dominated habitats but this proposed research will address the role of the alga in the synthesis of natural products, establish gene transcription at early stages in the interaction, and examine ecological benefits and isolation of natural product genes for biotechnology. This research has the potential to discover new bioactive molecules and measure impact of environmental change on the maintenance of boreal biodiversity.