When plants learn to defend themselves: the story of acacia and antelope

We are in 1981 and kundu, a variety of antelope bred in South Africa, becomes “famous” all over the world for being one of the first animals to practice mass suicide.

In South Africa’s national parks, many specimens of this animal were found dead and on an empty stomach. Lifeless, they lay at the foot of the acacias where they usually went to feed on the leaves of this tree.

After various investigations, autopsies and tests on plants, an incredible conclusion was reached: the reason for the “suicide” of the antelopes was born primarily from the presence of man-made fences that excessively limited their range of action but also and above all from the fact that the acacias, if excessively preyed upon, made their leaves toxic and therefore indigestible for antelopes.
Not only.

The acacia, thanks to a particular “communication” system, was able to send an ethylene-based gaseous message that warned nearby plants thus making other plants poisonous and inedible to kundu which, limited by fences, had no way of escape if not that of choosing between death by intestinal blockade or starvation.

After the period of excessive predation, the acacia leaves became edible again.

But how did these conclusions come about?

The team of Professor Wouter van Hoven of the University of Pretoria, mistreated and studied a forest of acacias to understand the intensity and duration of the “defense mechanism” of this plant.
Here is what conclusions he came to:

“Acacia trees send an” alarm signal “to other trees when antelopes eat their leaves. Wouter Van Hoven says that antelope-gnawed acacias produce leaf tannin in lethal quantities and emit ethylene into the air. Ethylene warns other trees of the imminent danger, which increases their tannin production for just five or ten minutes. Van Hoven made his discovery when asked to investigate the sudden death of about 3000 South African antelopes, called kudus, on the Transvaal ranches He noticed that the giraffe, who wandered freely, only ate from one acacia tree out of ten, avoiding those trees that were downwind. The Kudu, which was fenced in the ranches, could only eat acacia leaves during the winter months. the antelope continued to eat until the tannin from the leaves triggered a lethal metabolic chain reaction in his body. “