After the impact ofasteroid which swept away i dinosaurs and many plant species, a key event paved the way for a new alliance between ants and fungi. In a low-light environment, fungi, which feed on organic matter, became a crucial food source. The dust raised by the impact hindered the photosynthesis of plants, paving the way for the proliferation of fungi and favoring the development of mushroom-growing ants.
The asteroid impact 66 million years ago led to a dramatic decline in sunlight, killing much of the vegetation and animals. Mushrooms, capable of living in these conditions, found fertile ground. The scientists discovered that this growth of the mushrooms provided the opportunity for the ants to enter into a strategic collaboration: cultivating them as source of nourishment. This link between ants and fungi, known as mutualismproved fundamental for the survival of both species in such critical times. André Rodriguesco-author of the study and professor at the Institute of Biosciences of the State University of São Paulo, Brazil, explains:
The understanding of the origin of fungus-farming ants was already quite solid, but a precise chronology for these microorganisms was lacking.
The new research, published on Scienceprovided the smallest margin of error ever obtained for the emergence of these fungi, originally considered more recent.
Analyzing the genetic remains of 475 species of fungi cultivated by ants across America, the researchers focused on ultraconserved elements in fungal genomes. These genetic areas resist change during evolution and represent a direct link to the most ancient ancestors, as the co-author explains Pepijn Wilhelmus Kooijresearcher supported by FAPESP:
We studied the regions close to these elements, where the most recent differences between species reside, managing to trace a rather accurate evolutionary line.
Thanks to these analyses, scholars have identified two distinct lines of fungi, deriving from a common ancestor of current leaf-cutter ants, dating back 66 million years ago. Furthermore, a correlation emerged with coral fungi, cultivated by ants around 21 million years ago.
A strategic adaptation to the post-asteroid era
Ancestral ants, the authors suggest, lived in close contact with fungi, feeding occasionally or cultivating them in their colonies. Mutualism between fungi and ants became indispensable after the asteroid impact: fungi needed ants to feed and reproducewhile ants used fungi as their primary source of nourishment. In modern times, four different groups of ants cultivate as many types of fungi, even influencing their development to obtain specific nutrients. Kooij points out:
When we grow fungi in the laboratory, they take on the expected shape of hyphae. However, within the colonies, one of these types of hyphae swells to form structures similar to grapes, rich in sugars. We still don’t know how ants do it.
With the emergence of savannas about 27 million years ago, environmental diversification offered new evolutionary possibilities for both ants and fungi. The ants colonized larger territories, evolving into what is now known as the species of leaf cutterthus promoting the diversification of fungi. This latter ability of fungi to effectively decompose organic matter is now being studied as a potential method for degrading other materials, such as plastic.
