Tropical ecosystems rely on the infrastructure provided by termites. These insects supply plants with vital nutrients by breaking down organic waste, bringing water to the roots by aerating the soil through tunneling, and sustaining the food chain, as they make up an estimated 10-20% of the total biomass of rainforests. But termites were not always the backbone of tropical ecosystems.
Now, we know how the ecosystem engineers of the rainforest rose to prominence. By exhaustively sequencing DNA of almost all termite species across the Americas, including 206 new to science, researchers from the Okinawa Institute of Science and Technology (OIST) and international colleagues have mapped the insects' evolutionary timeline. The results show that the traits that define modern termites — such as soil-eating, nest construction from fecal matter, and fungus agriculture — emerged not gradually, but in two distinct pulses about 30 million years apart, following the End-Cretaceous and Eocene-Oligocene extinction events. Their findings were published in Current Biology today.
Eating dirt to thrive
Both waves of termite diversification occurred during periods of global ecosystem collapse. The exact trigger for the first wave is still hypothetical. It occurred around the end of the Cretaceous, possibly coinciding with the impact of a 10 km-wide meteor that ended the reign of the dinosaurs 66 million years ago. "The End-Cretaceous event likely contributed to the extinction of some termite lineages, but it probably also left many ecological niches open, which could have promoted their diversification later on," says study co-first author Dr. Simon Hellemans.
The second wave occurred directly after the Eocene-Oligocene extinction event, about 33 million years ago. Here, the continental separation of Australia and Antarctica formed an ocean current that isolated Antarctica's climate, creating the conditions necessary for permafrost. The emerging glaciers sponged up global seas and triggered a geologically rapid global freeze: over about 10,000 years, the average global temperature fell by 8 °C. Professor Thomas Bourguignon from the Evolutionary Genomics Unit at OIST explains: "Before the Eocene-Oligocene extinction event, hot rainforests ranged from what's now Alaska to the northern tip of Antarctica. But after the global cooling, rainforests were confined to the tropics. Many hot rainforests were rapidly transformed into temperate forests and savannas."
While the global freeze killed off countless plant and animal species, one group of termites had achieved a breakthrough innovation just shortly before. "The ability to digest soil gave termites of the family Termitidae a new niche to colonize. Many ecological niches had been cleared by the extinction event, which the soil-eaters could now specialize in," says Bourguignon. Today, soil-feeding termites make up more than half of all termite species. Pest species make up a small fraction of the remaining wood-eating termites.
The rapid expansion and diversification of Termitidae can partly be explained by their ability to eat soil, but how they spread across the seas remains unknown. While they originated in Africa, their descendants are now found worldwide, including in the Americas, which drifted away from Africa well before the order evolved. Wood-eating termites have previously been found to travel across oceans on fallen trees, but Termitidae need soil to survive. Hellemans continues: "It's mysterious. One speculation is that they survived in clumps of soil stuck on upturned tree roots, or maybe plant growth in tree canopies — but we don't have evidence for this yet."
Sequencing the Americas
The team's findings were built on a massive expansion of the termite genomic database. "We sequenced 1,756 new samples, doubling the total number of available mitochondrial genomes and vastly expending nuclear data," recounts Hellemans. "We now have access to genetic data of almost all termite species across the Americas, giving us a clear view into their evolutionary history. Incidentally, we've also obtained genetic data for more than 200 species new to science. This dataset should give taxonomists work for the next decade or so."
While Hellemans and Bourguignon themselves collected some termites from South America, the database is largely built on collections provided by the Museum of Zoology of the University of São Paulo in Brazil, the University of Florida in the United States, and the Université Libre de Bruxelles in Belgium.
"We now know that strong resilience to global ecological upheaval was central to termite diversification," summarizes Bourguignon. "But while it's too early to assess the effects of global warming on the trajectory of their evolution, many species have most likely already been lost to human-driven ecosystem changes such as deforestation." With the new evolutionary timeline and database, we now have a much clearer view of how termites have become indispensable engineers of tropical ecosystems, and why their resilience matters as we humans reshape the planet.
