Well-traveled wood eaters: Biologists have reconstructed for the first time how dry wood ants conquered the world. Thus, these wood eaters must have crossed entire oceans dozens of times in the course of their expansion in order to colonize new territories. Termites completed some of these crossings inside floating logs. On the other hand, in the recent past, they mostly traveled as stowaways in ship wood.
Termites have a bad reputation. Huge buildings in some termite countries cause astonishment and respect. However, most people associate these social insects with destroyed wood and crumbling wooden buildings. Dry wood ants (Kalotermitidae) are responsible for this, using the wood as a nesting place, food and protection at the same time. This group includes some of the most feared invasive pests, and dry wood ants are now found in almost all parts of the world.
But how and when the wood-eating termite spread so widely has only been partially elucidated so far. A team led by Ales Bucek of the Okinawa Institute of Science and Technology has reconstructed the evolutionary history of dry wood ants using genetic means for the first time. For their study, the researchers analyzed the mitochondrial genomes of about 120 Calutermitide species from 21 out of 23 genera in this termite family.
The result is the first comprehensive family tree of dry wood ants, which not only shows their evolution but also reconstructs when the species invaded any area. The common ancestor of all calothermitides split from the rest of the cockroach-like insects about 115 million years ago. About 84 million years ago, somewhere in the modern tropics, Central America today, one of its descendants evolved to become the ancestor of all the more advanced modern dry wood ants.
Across the sea on a wooden raft…
However, the exciting thing is that over the past 50 million years or so, different genera of dry wood ants have spread from the neotropics all over the world—even conquering the oceans in the process. “The calothermitides must have invaded new biogeographic regions at least 40 times, mostly through transoceanic spread,” Bucek and colleagues say.
Termites even cross the big seas, for example to move from the new tropics to Africa or Europe. Their way of life in wood has provided them with the perfect tools: “Their wooden houses are rafts,” Bucek says. Because wood floats, insects were able to drift long distances by themselves with branches, trunks, and other driftwood. “It makes them very good at crossing oceans.”
… or stowaway on a ship
But more recently, termites have used another strategy: They traveled on ships as stowaways. Hiding in the wood of shipboards, many species of wood-eating termites have reached new territories, including the infamous invasive species of the genus Cryptotermes. They spread from Central America through the Caribbean and the USA to South America, Africa and southern Europe. These wood-eaters even made their way to Australia and New Zealand thanks to human trade and transport routes.
“Ocean travel and, more recently, human-mediated dispersal have been the most important drivers of the global distribution of the Kalotermitidae chain,” say the researchers. (Molecular Biology and Evolution, 2022; doi: 10.1093/molbev/msac093)
Source: Okinawa Institute of Graduate University of Science and Technology
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