New Publication: Incomplete degradation of lichen acids in Svalbard reindeer

Photo: Monica A Sundset

Prof. Monica A Sundset from our research group together with colleagues in Poland recently published a new study investigating whether Svalbard reindeer are capable of degrading lichen secondary compounds such as usnic acid and atranorin. Do Svalbard reindeer seek and eat terricolous and fruticose lichens — the only sources of these two substances in Svalbard — and are they able to degrade these lichen secondary compounds?

Lichens are associations between fungi and algae or cyanobacteria. They synthesize a large variety of secondary metabolites serving diverse functions, including defence against herbivory and microbes. Usnic acid and atranorin are perhaps the most studied of these lichen secondary compounds, absorbing and protecting the lichen from UV radiation.

Atranorin is antibacterial, but its toxicity has not been shown in animal models so far, while usnic acid can be toxic to both animals and humans and even lethal in high doses, as shown for sheep. Still lichens may contribute to large proportions of the winter diet of reindeer in Subarctic and Arctic areas. It is not fully understood how reindeer cope with such high intakes of lichen secondary compounds. There may be several answers to this, but studies so far have indicated that usnic acid and other phenolic secondary compounds are detoxified through microbial degradation in the rumen. In addition, endogenous enzymes in the intestine and/or the liver of the animal may also contribute to detoxification. If not degraded or only partly degraded, and not absorbed, secondary compounds will appear in faeces.

The Svalbard reindeer is the northernmost herbivorous mammal in the world and are adapted to austere nutritional conditions. During the short Arctic summer, Svalbard reindeer feed on a lush tundra vegetation of vascular plants, including grasses, herbs, sedges and deciduous shrubs in the lowland plains and valleys, to accumulate fat for the winter. These body reserves are usually exhausted in early winter and for the rest of the winter the reindeer rely on pastures along mountain slopes, plateaus and ridges where less snow accumulates. The winter diet consists of bryophytes and fibrous vascular plants. Optimal utilization of these poor-quality, fibrous forages is crucial for survival through the long, cold winter, and the Svalbard reindeer has adapted a unique rumen microbiome that is effective in degrading cellulose and plant biomass.

Fecal samples were collected in Bolterdalen valley at Svalbard together with vegetation samples from the study site. The mesic tundra in this area was dominated by vascular plants (59% of vegetation cover), but Bryophytes (16%) and lichens (25%) were also present.

Atranorin and usnic acid were detected in the faecal samples using high-performance liquid chromatography. This shows that lichens are indeed included in the diet of Svalbard reindeer, although probably in small amounts because of depleted pastures. But contrary to previous findings in reindeer on mainland Norway, atranorin and usnic acid are not completely degraded or absorbed in Svalbard reindeer. To elucidate the mechanisms behind detoxification of lichen secondary compounds in reindeer, more research is needed on their respective rumen microbiomes and digestive enzymes.

For full reference read:
Wegrzyn M, Wietrzyk P, Cykowska-Marzencka B, Galanty A, Sundset MA (2019) Incomplete degradation of lichen usnic acid and atranorin in Svalbard reindeer (Rangifer tarandus platyrhynchus). Polar Research 38: 3375