Lichens thrived, diversified after the dinosaurs died out

The dinosaurs were the most famous victim of the asteroid that struck Earth some 66 million years ago, but the mass extinction event also killed off a variety of plants and animals. According to a new study, the loss of plant life created space for lichens to diversify and thrive.

Lichens are composite organisms formed by symbiotic relationships between algae or cyanobacteria and different fungi species.

"We thought that lichens would be affected negatively, but in the three groups we looked at, they seized the chance and diversified rapidly," Jen-Pang Huang, a former postdoctoral researcher at the Field Museum in Chicago, said in a news release. "Some lichens grow sophisticated 3D structures like plant leaves, and these ones filled the niches of plants that died out."

The asteroid that marked the end of the Cretaceous period sent dirt, ash and debris high into the atmosphere -- as did the volcanic activity that was triggered by the impact -- blocking out the sunlight that plants rely on for food.

"We originally expected lichens to be affected in a negative way, since they contain green things that need light," said Huang, who now works as a researcher at Academia Sinica in Taipei.

Because there are very few lichens preserved in the fossil record, scientists had to study the genomes of modern lichens to better understand their past successes and failures. From studying lichens in the lab, scientists have a pretty good understanding of how many mutations lichen DNA acquires over time -- the mutation rate.

When the mutation rate is known, a comparison of the genetic sequences from different but related species can reveal how long ago the pair split from a common ancestor. For the study, Huang and his colleagues used a computer model to analyze the genetics of three different families of lichens. The results showed groups of leafier lichens expanded in the wake of the dinosaurs' disappearance.

"Some groups don't show a change, so they didn't suffer or benefit from the changes to the environment," said Thorsten Lumbsch, the Field Museum's curator of lichenized fungi. "Some lichens went extinct, and the leafy macrolichens filled those niches. I was really happy when I saw that not all the lichens suffered."

The findings, published this week in the journal Scientific Reports, can offer new insights into how different types of organisms are impacted by sudden environmental changes and mass extinctions.

Scientists hope the latest research -- and similar followup studies -- will continue to unravel the mysteries of the fungus kingdom and explain how the world's fungus families came to look and behave like they do.

"We expect a lot of patterns from studying other organisms, but fungi don't follow the pattern. Fungi are weird," said Huang. "They're really unpredictable, really diverse, really fun."

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