In my occasional series, “When Plants Attack” we’ve seen some of the ways in which plants can defend themselves. So far I’ve covered the chemicals they produce to discourage other plants from growing in their space (allelopathy) and the conventional weaponry they use to guard against a physical attack. I am planning more posts to continue the series, which will include a look at the chemical defences plants have evolved to protect themselves against being eaten. But as soon as a plant evolves a defence mechanism, predators will begin to evolve or develop a way to counteract it. For example, some insects can collect poisons from the plants they’re munching on, and use them as part of their own defences. But until now it has seemed as though plant-eating mammals change their behaviour to cope with toxic plants – e.g. by changing how they forage for food, or by eating dirt (geophagy) to detox.
On Wednesday a paper published in Biology Letters put forward what the authors believe is the first evidence of large mammals evolving to combat a plant’s chemical defences. The researchers collected saliva samples from moose (Alces alces) and European reindeer (Rangifer tarandus) in Canadian zoos, whilst the animals were anesthetized to undergo necessary medical procedures. These two animals are known to feed on red fescue (Festuca rubra), a grass which occurs around the world. Red fescue uses a common defensive strategy: it forms a mutually-beneficial relationship with a fungus (Epichloë festucae), which produces toxic alkaloids.
By applying the animal saliva to grass samples, the researchers demonstrated that both moose and reindeer saliva slowed down the growth of the fungus, and so reduced the amount of toxin that was produced.
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