Reindeer lichens reproduce sexually far more than scientists thought


While reindeer lichen can produce both sexually and asexually, researchers were surprised at the genetic diversity found in lichens in Northern Canada -- because it means they are more sexual than previously thought. Photo by Marta Alonso-García

Jan. 29 (UPI) -- Like most lichen, reindeer lichen can reproduce both sexually and asexually, by sending out spores or simply cloning themselves.

Previously, researchers assumed reindeer lichen, Cladonia stellaris, was primarily a clonal species, and would therefore feature relatively low levels of genetic diversity.

But according to a new genomic survey, published Friday in the American Journal of Botany, the reindeer lichen that blanket the forest floors of northern Canada have been doing a lot more gene-mixing than scientists thought.

In other words, reindeer lichen have been having plenty of sex.

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Lichen are composite organisms featuring fungi and algae. Algae provide energy via photosynthesis, while the fungi secure nutrients from organic matter in rocks, soil and bark.

When lichen reproduce sexually, neighboring lichen exchange genetic information through intertwined root-like structures. The lichen then release single-cell spores.

Dispersed by wind, the spores colonize new territory, sprouting genetically distinct lichen.

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During asexual reproduction, lichen pinch-off a bit of themselves. This bit of fungi and algae, called the thallus, establishes a separate lichen that is genetically identical to its parent.

Ubiquitous and often inconspicuous, lichen are vital -- and according researchers, under appreciated -- members of forest ecosystems.

"Services provided by lichens are countless," lead study author Marta Alonso-García, postdoctoral fellow at Laval University in Quebec, told UPI in an email. "For example, together with mosses, they are the first organisms to colonize the soil after a fire."

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"In particular, reindeer lichens have adapted better than almost all other lichens to boreal biome, the largest biome in North America," said Alonso-García. "Cladonia lichens have become essential components of those ecosystems and, in winter, they represent the most important food source for reindeer and caribou. In addition, they contain about 20 percent of the total lichen woodland biomass and can contribute up to 97 percent of ground cover."

To better understand the relationships between the reindeer lichens growing in the forests of northern Canada, researchers extracted and sequenced the DNA from dozens of lichen samples. Researchers focused on the DNA of the lichen's fungi.

Researchers were surprised to find a significant amount of genetic variation among lichens growing in different parts of the forest.

Sexual reproduction can help organisms rid themselves of potentially harmful gene mutations and accumulate potentially useful genetic variations. But sexual reproduction requires more energy, making it a riskier strategy.

Sexual reproduction is also more difficult for symbionts like lichen.

"Asexual reproduction has the advantage that the fungus reproduces together with the algae -- lichen parts breaking apart," study co-author Felix Grewe told UPI in an email.

"In comparison, sexual reproduction by fungal spores requires a reacquisition of the algal/cyanobacterial symbiotic partner wherever the wind dispersed spore lands," said Grewe, co-director of the Field Museum's Grainger Bioinformatics Center.

Though reindeer lichen are apparently having more sex than expected, under certain circumstances the lichen are still opting for asexual cloning.

Researchers found that reindeer lichen were much more genetically homogenous across recently burned forest.

The discovery was another surprise. Scientists assumed the thallus pieces that enable asexual reproduction would be easily destroyed by fire.

In followup studies, researchers said they hope to directly observe the reproductive behaviors of reindeer lichen in order to confirm the conclusions of their genetic analysis.