Ants and plants: A 60-million-year-old evolutionary friendship

Ants and plants: A 60-million-year-old evolutionary friendship
Scientists have modeled the humble ant's evolution and found it's inextricably linked to plants
Scientists have modeled the humble ant's evolution and found it's inextricably linked to plants
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Scientists have modeled the humble ant's evolution and found it's inextricably linked to plants
Scientists have modeled the humble ant's evolution and found it's inextricably linked to plants

Ants can be found in huge numbers in almost all of the world’s regions and habitats. But how did they become the most populous, highly diverse insect species on the planet? Scientists may have an answer, and it has to do with plants.

About 60 million years ago, ants were mainly forest dwellers who built their nests underground. But the modern ant has diversified into more than 14,000 species, with some now living in savannas, grasslands, and deserts. In fact, ants can be found on every continent except Antarctica.

Previous studies have demonstrated that ant diversification coincided with the rise of angiosperms, plants that produce flowers and bear their seeds in fruits. What’s less clear, though, is the role that flowering plants played in the evolution of ants and how we reached the number of individual ants we see today, which is estimated to be more than four quadrillion – that’s a four followed by 15 zeros.

Now, researchers from the Field Museum in Chicago, and Cornell and Stanford Universities have looked to fossils, DNA, and climate data to discover how ants and plants are linked, evolutionarily speaking.

“When you look around the world today, you can see ants on nearly every continent occupying all these different habitats, and even different dimensions of those habitats – some ants live underground, some live in the canopies of trees,” said Matthew Nelsen, lead author of the study. “We’re trying to understand how they were able to diversity from a single common ancestor to all these different spaces.”

To model the ant’s evolution, researchers compared the climates that 1,435 modern ant species live in and added time-scaled reconstructions of ant genealogy based on genetic information and ant fossils preserved in amber. They obtained similar information on plants and then compared the two.

The findings suggested that most early ants occupied forested habitats until around the middle-to-late Paleogene period (66 to 23 million years ago) to the early Neogene (23 million years ago to present). It was at that time they started diversifying, influenced by the evolution of forest plants.

“Around this time, some of the plants in these forests evolved to exhale more water vapor out through tiny holes in their leaves – they made the whole place a lot wetter, so the environment became more like a rainforest,” Nelsen said.

To escape the wet, some ants moved their nests from underground into the trees. The researchers suggest that as forest angiosperms slowly spread outward to inhabit more open, arid regions, some of the ants followed. Probably, the researchers said, because they were following their stomachs.

“Other scientists have shown that plants in these arid habitats were evolving ways of making food for ants – including things like elaiosomes, which are like fleshy appendages on the seeds,” said Nelsen.

A mutually beneficial relationship developed. The ants enjoyed the food provided by the plant’s seeds, and the ants taking the seeds ensured that the plants were spread even further.

The study's findings improve our understanding of how ants' evolution coincides with and was enabled by the evolution of flowering plants, starting millions of years ago.

“This study shows the important role that plants play in shaping ecosystems,” Nelsen said. “Shifts in plant communities – such as those we are seeing as a consequence of historic and modern climate change – can cascade and impact the animals and other organisms relying on these plants.”

The study was published in the journal Evolution Letters.

Source: Field Museum

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