Ants and fungi: the unlikely alliance that emerged after the asteroid impact

The asteroid that wiped out the dinosaurs 66 million years ago caused the spread of fungi that allowed ants to survive in a light-free environment

This unlikely alliance between ants and fungi was the main inspiration for their finding-made possible by a critical development after an asteroid impact had wiped out the dinosaurs and a great deal of plant life. The impact threw dust and particles into the air that blocked sunlight, disturbed plant photosynthesis, and let fungi thrive-optimal conditions for the evolution of fungus-farming ants.

After the asteroid: 66 million years ago

The impact of the asteroid some 66 million years ago drastically reduced the amount of sunlight, therefore killing most of the vegetation and animal life. Fungi are capable of living in low-light conditions and therefore harnessed a new ecological niche. Fruiting bodies of fungi have been found and studied by scientists, who report that this very growth gave ants a peculiar survival opportunity: to cultivate fungi as a food source. This mutualistic relationship between the ants and fungi proved to be life-saving during these stressful times for both species. André Rodrigues, a co-author of the study and professor at the Institute of Biosciences at São Paulo State University in Brazil says:

“The understanding of the origin of fungus-farming ants was already pretty solid, but we were missing a precise timeline for these microorganisms.”

The new study, published in Science today, places a timeline on when these fungi emerged that is considerably more accurate than the rough estimates of its origin thought to be more recent.

Tracing Evolution Through Genetic Analysis

They studied the genetic leftovers from 475 species of fungi farmed by ants throughout the Americas. They looked for highly conserved regions within fungal genomes, regions resistant to change over time and that link back to ancient ancestors. According to co-author Pepijn Wilhelmus Kooij, researcher funded by FAPESP:

“We looked at the regions around these conserved elements, and there the more recent differences between species reside, which allowed us to map a reasonably precise evolutionary line.”

Using these types of analyses, researchers traced two separate fungal lineages from a common ancestor through to living leaf-cutting ants, going back 66 million years. They also found one that correlated with coral fungi being cultivated by ants about 21 million years ago.

Strategic adaptation in the aftermath of an asteroid impact

The authors theorize that ants lived in a close relationship with fungi in ancient times, either as opportunistic feeders or as cultivators within their colonies. After the asteroid impact, the interdependence of fungi and ants became a necessity: fungi needed the ants for nutrition and dissemination, while ants needed fungi as a primary food source. Nowadays, four independent lineages of ants host different fungal types, controlling the growth of fungi for optimal nutrient production. In the words of Kooij:

“When we cultivate fungi in the laboratory, they assume the hyphal structure as anticipated. However, in the colonies, a type of hyphae inflated into grape-like clusters that were rich in sugar. And it is still unknown how ants manage to induce this.”

With the rise of the savannas, about 27 million years ago, new evolutionary opportunities opened up for both ants and fungi. The ants dispersed to much wider ranges, evolving into what we now call leaf-cutting ants and, in the process, furthering fungal diversification. Nowadays, scientists study the fungi for their ability to effectively degrade organic matter as a potential means to break down synthetic materials like plastics.

Source: Science