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http://www.naturalhistorymag.com/htmlsite/0702/0702_feature.html
They look like the curlicue-topped mountain that overlooks the Grinch’s Whoville: cones of soil and sand, up to thirty feet tall, topped with earthen spires pointing toward the noon sun. Common on the savannas of southern Africa, they are termite mounds, constructed by the fungus-cultivating termite Macrotermes michaelseni. Locals call these structures "ant heaps." In Afrikaans, termites are rysmeere (literally, rice ants); sometimes the insects are called white ants. Termites are not ants, however: their ancestors are social cockroaches, not the wasps from which ants descend. And neither is the termite mound a heap, a haphazard pile of dirt. Opening it reveals a complicated internal architecture: a capacious central chimney from which radiates a complex network of passages, connecting ultimately to an array of thin-walled tunnels that lie under the mound’s surface like veins on an arm. Most interesting, though, is what you do not see: termites. The mound is not a habitation for the millions of termites that built it. Their residence is a nest below the mound, a spherical underground city about six feet in diameter.
Entomologists have long ascribed respiratory functions to these termite mounds, and for many years they thought the mound’s workings were pretty well understood. It was a fine story, first told in the late 1950s by Swiss scientist Martin Lüscher, who was investigating the mounds of Macrotermes natalensis. Lüscher had the ingenious, but at best only partly correct, idea that a colony’s metabolism could power its ventilation and maintain the nest’s remarkably constant temperature. The energy of the termites’ collective "hot breath" heated the air in the nest, Lüscher surmised, and the warmed air would waft up through the mound’s tunnels. The air rising from the nest would eventually cool and pass down again through the conduits near the mound’s surface. In these passages, the air would be refreshed by diffusion through the structure’s porous walls before being sent on another circuit through the nest.
A puzzling question remains, however. The fungi are the major heavy breathers in the nest, consuming oxygen about five times faster than the termites do. Why, then, do the termites work so hard to build an earthen lung if the fungi, Termitomyces, actually do the most to make the nest air stuffy? To be sure, the act is not altruistic, because the fungi, by breaking down the termites’ food, are performing a critical function. In a sense, the termites are "paid" for their work. But the fungi may be gaining much more than simply having termites supply them with a steady diet of cellulose: Termitomyces, you see, have competitors.
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发表于 2018-9-26 12:45:32
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