Partner swapping: a climate change survival strategy

Some species of lichen grow under very different climatic conditions. They are true survival artists. Now new research published in New Phytologist suggests that the secret to their success lies in their willingness to be unfaithful to their algal partners.

Lichens are a classic example of symbiosis, in which a species of algae moves in with a fungus and, in exchange for shelter, provides food via photosynthesis. Researchers from Frankfurt have now discovered that the identity of the algal partner could play a crucial role in how well the lichen-forming fungus copes in different climates.

Picky partners

“We were able to prove that the lichen-forming fungi Lasallia pustulata and Lasallia hispanica live together with different green algae from the genus Trebouxia, depending on their location,” said Prof. Imke Schmitt of the Senckenberg Biodiversity and Climate Research Centre. “There is a different climate at the locations. The assumption is therefore obvious that the exchange of algal partners is a mechanism that lichen-forming fungi use to adapt to different climatic conditions.”

The researchers decided to study the the two closely related lichens because they live at different altitudes, but also grow together in the middle altitude range. Taken together, their habitat in the Mediterranean extends from 0 metres up to 2,100 metres above sea level. As conditions become considerably colder and wetter with increasing altitude, this proved an ideal area in which to test the influence of the climate on the fungal-algae symbiosis.

Cross-section of Lasallia pustulata showing the green algae (green upper layer) and fungal symbiont (white). Copyright: Francesco Dal Grande.

Fair-weather fungi

The researchers used high-throughput molecular biology techniques and analysed about 23 million green algae DNA sequences to find out exactly which fungus lives with which algae partner. “The lichen-forming fungi can theoretically live together with seven different Trebouxia species. But do not do it everywhere. There are both ‘fair weather’ partners for warm, frost-free environments in the valley and ‘bad weather’ partners for the high altitudes,” said Schmitt.

But the choice of partner isn’t just based on climate – the fungi have certain preferences. If both species, Lasallia pustulata and Lasallia hispanica, occur in the same place and there are also several species of algae, the fungi act on their own preferences to pick different partners.

Image: The South face of the Sierra de Gredos mountain range, seen from Oropesa (Toledo). Source: Wikimedia Commons, user: FDV. CC BY-SA 3.0.
The South face of the Sierra de Gredos mountain range, where the lichen were collected, seen from Oropesa (Toledo). Source: Wikimedia Commons, user: FDV. CC BY-SA 3.0.

Swapping partners adapt faster

If the lichens do swing between climatic extremes by switching algal partners, they would have an advantage over other organisms. “It’s possible that the lichen-forming fungus could make it within a few generations, instead of living with the previous species of algae rather than another that is more adapted to the new environmental conditions,” explains Schmitt, adding, “That would be significantly faster than adapting to new climatic conditions by changing genetic material. This ‘classic way’ can last millions of years.”

Adapted from a press release.

Read the paper: Dal Grande, F., Rolshausen, G., Divakar, P. K., Crespo, A., Otte, J., Schleuning, M. and Schmitt, I. (2017) Environment and host identity structure communities of green algal symbionts in lichensNew Phytologist. doi: 10.1111/nph.14770


 

Mike Whitfield (@mgwhitfield)
Development Coordinator
New Phytologist