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The dating of this unique parasitic association to the mid-Palaeogene indicates a deep-time origin for the behavioral manipulation of an ant host by a fungal pathogen, according to Labandeira. “And this [link widoczny dla zalogowanych],” says Hughes “pinpoints the fungally-induced behavior modification of what were likely ancient carpenter ants to a time after ant lineages had diversified a
The well-studied carpenter ant population in southern Thailand provides a close modern parallel for the distinctive type of leaf damage made by mandibular death grips. When a doomed ant secures itself onto a leaf in the rain forest understory it leaves a pair of widened mandibular puncture marks surrounded by callused tissue on each side of a primary or secondary vein. “Importantly,” says Hughes “the bites left by the ant on the leaf blade are distinctive and centered on major veins; the choice of the leaf host taxon by the ant is non-selective and based overwhelming on environmental clues of favorable temperature and humidity for growth of its fungal parasite near the forest floor.”
So Hughes contacted Conrad C. Labandeira, a palaeoecologist at the Smithsonian’s National Museum of Natural History in Washington, DC who was working at Messel Pit fossil site in Hesse, Germany. Serendipitously, Labandeira had noted strange markings on an ancient leaf which had puzzled him for years.
Modern Zombie Ants Leave the Same Bite Marks on Leaves as Their Distant Ancestors
Pinpointing the Origins of Ant-Fungal Parasitism
Forty-eight million years ago a hapless ant was dying to help a ruthless fungus reproduce. This moment [link widoczny dla zalogowanych], the oldest known example of a parasite manipulating insect behavior, was recently caught in time by behavioral ecologist David P. Hughes at Harvard University, Cambridge, Massachusets in collaboration with scientists from the Smithsonian Institute in Washington DC and the Steinmann Institute at the University of Bonn in Germany.
Many parasites have evolved the ability to alter host behavior in ways that promote their own fitness, says Hughes “But one of the most impressive examples of adaptive manipulation is the death grip of ants infected by the fungus Ophiocordyceps unilateralis.” In this system, the fungus turns ants, usually carpenter ants [link widoczny dla zalogowanych], like one formally known as Camponotus leonardi, into “zombies,” making them leave their nests, travel a long way to find the perfect place for fungal spore production and attach firmly to major veins on the undersides of low-hanging leaves with their mandibles before being killed.
This death-grip behavior, biting down hard on a major leaf vein, keeps the ant’s dead body firmly in place for spore production - but it also leaves very distinct scars on the leaf and Hughes wondered if clues to the origins of ant-fungal parasitism could be found in the fossil past. “Many fungi manipulate insects to bite major leaf veins in a similar manner to O. unilateralis,” he says, “thus this type of manipulation seemed likely to be captured on fossil leaves.”
The Messel Pit, a World Heritage Site, is the richest source in the world for understanding the living Eocene environment, between 57 million and 36 million years ago. Insects are among its most frequently found fossils, thus Hughes and his colleagues who now included Torsten Wappler, a paleontologist from the Steinmann Institute in Bonn, began examining leaf specimens stored in the Messel plant collection. A single leaf of the dicotyledonous plant host Byttnertiopsis daphnogenes had the distinctive, dumbbell-shaped mandible cut marks made by fungal manipulation of an ant host’s mouthparts. “The bites couldn’t be anything else,” Hughes stresses, “because the location on the leaf vein and shape of the parks are so unusual.”
Death-grip of a Dying Ant Provides Telltale Signs of Ancient Fungal Parasitism