Prehistoric meat-eating fungus snared microscopic worms

Cowboys have been lassoing cattle for several centuries, but it turns out that fungi developed the same trick 100 million years ago when dinosaurs still walked the Earth.

Alexander Schmidt and colleagues from the Humboldt University of Berlin found evidence of this ancient Wild West scene in a beautiful chunk of French amber.

The amber piece lacked the transparent clear beauty of a jeweller’s piece and the debris and dirt inside it suggests that it came from tree sap that had fossilised after it had fallen to the ground. There, it perfectly preserved the species living in the leaf litter, including a species of predatory fungi and the small worms – nematodes – that Schmidt thinks it hunted.

The fungus’s weapons were single cells coiled into rings just 10 micrometres in diameter. A thousand of these tiny loops could fit in a centimetre, but they were more than large enough to accommodate a blundering nematode. Once a worm swam through, the fungi constricted its snare, trapping the animal.

The cellular lassos sometimes broke off from the main fungal cells and Schmidt found that many of these loose rings clumped together. According to him, this probably means that the rings were coated with a sticky glue to better ensnare their nematode prey.

In the soils of today, over 200 species of carnivorous fungi feast on nematodes, using similar lassos (see right) along with sticky knobs and nets. From them, Schmidt could guess at the grisly fate of the ancient trapped worms. Most likely, the fungus would have penetrated its body with root-like projections from its cells called ‘infestation hyphae’ and drawn out the nutrients it needed.

But modern species differed from the fossilised one in important ways. The ancient species created lassos from single cells, while modern ones use three. And unlike contemporary species, the fossilised one had a secondary life cycle, where it formed reproductive spores instead of lassos.

To Schmidt, this means that the fungus in the amber was not a forerunner of today’s nematode trappers; it may well have no living descendants. Instead, the innovation of a cellular lasso probably evolved independently several times during Earth’s history.

A word of caution though: Schmidt’s conclusions are, for the moment, an educated guess. The nematodes were only ever found near the rings and Schmidt concludes that they were nematode traps because they are the right size and because modern fungi use similar rings. Until he finds the fossil remains of a ring actually ensnaring a nematode, his interpretation is up for debate.

Images: Amber image from Science paper; black-and-white image by Allin & Baron.

Reference: Schmidt, A.R., Dorfelt, H., Perrichot, V. (2007). Carnivorous Fungi from Cretaceous Amber. Science, 318(5857), 1743-1743. DOI: 10.1126/science.1149947

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