Researchers have pinpointed how years of civil war and poaching in Mozambique have led to a greater proportion of elephants that will never develop tusks.
“When we think about natural selection, we think about it happening over hundreds, or thousands, of years,” said Samuel Wasser, a conservation biologist at the University of Washington. “The fact that this dramatic selection for tusklessness happened over 15 years is one of the most astonishing findings.”
Now scientists are studying what more tuskless elephants means for the species and its savannah environment. Their preliminary analysis of fecal samples suggests the Gorongosa elephants are shifting their diet, without long incisors to peel bark from trees.”
(Shane C. Campbell-Staton et al. “Ivory poaching and the rapid evolution of tusklessness in African elephants.” Science 22. October 2021, Vol 374.)
The survivors were likely to share a key characteristic: half the females were naturally tuskless – they simply never developed tusks – while before the war, less than a fifth lacked tusks.
Genes are responsible for whether elephants inherit tusks from their parents. Although tusklessness was once rare in African savannah elephants, it's become more common – like a rare eye color becoming widespread.
After the war, those tuskless surviving females passed on their genes with expected, as well as surprising, results. About half their daughters were tuskless. More perplexing, two-thirds of their offspring were female.
The years of unrest “changed the trajectory of evolution in that population,” said evolutionary biologist Shane Campbell-Staton, based at Princeton University.
Because the tuskless elephants were female, they focused on the X chromosome. (Females have two X chromosomes; males have one X and one Y chromosome.)
They also suspected that the relevant gene was dominant – meaning that a female needs only one altered gene to become tuskless – and that when passed to male embryos, it may short-circuit their development. Instead of having sons and daughters at an equal proportion, tuskless mothers gave birth to daughters roughly two thirds of the time.
“The study shows that tuskless male elephant offspring are not viable, meaning that population decline is accentuated. Not only do animals die due to poaching, but there is also additional decline because half of the male offspring from the surviving tuskless mothers do not survive.”
– Fanie Pelletier, ecologist at the University of Sherbrooke in Quebec, who co-authored a perspective piece in Science about the research.
“When mothers pass it on, we think the sons likely die early in development, a miscarriage,” said Brian Arnold, a co-author and evolutionary biologist at Princeton.
Their genetic analysis revealed two key parts of the elephants’ DNA that they think play a role in passing on the trait of tusklessness. The same genes are associated with the development of teeth in other mammals.
"The tuskless females ate mostly grass, whereas the tusked animals ate more legumes and tough woody plants," said Robert Pringle, a co-author and biologist at Princeton University. “These changes will last for at least multiple elephant generations.”
The work “helps scientists and the public understand how our society can have a major influence on the evolution of other life forms.”
(Associated Press. “Elephants have evolved to be tuskless in response to ivory poaching, study finds.” NBC News. October 22, 2021.)
Implications
“I think it’s easy when you hear stories like this to come away thinking, ‘Oh everything’s fine, they evolved and now they’re better and they can deal with it. But the truth is that species pay a price for rapid evolution. Selection always comes at a cost, and that cost is lives.”
– Dr. Shane Campbell-Staton
Among Asian elephants, a long history of hunting for ivory – as well as removing tusked elephants from the wild for labor – likely helped contribute to higher tuskless numbers there.
“If you look at Asian elephants, females don’t have tusks at all, and depending on which population you look at in which country, most males are also often tuskless,” Joyce Poole, an elephant behavior expert and scientific director of a nonprofit called Elephant Voices, explains. Exactly why the Asian and African elephant populations have such different rates of tusklessness remains unexplained.
Yet Poole and others note that in areas in Asia that historically have been targeted for ivory hunts, tuskless levels are high – just as in Africa – underscoring that humans are leaving a lasting mark on Earth’s largest land mammal.
If elephants are changing where they live, how quickly they move, or where they go, it could have larger implications for the ecosystems around them. The work elephants do with their tusks is vital for other animals too.
“Elephants’ role as a keystone species to topple trees and dig holes to access water is important for a variety of lower species that depend on them,”says Ryan Long, a behavioral ecologist at the University of Idaho and a National Geographic Explorer. Tusk action also helps create habitats. Certain lizards, for example, prefer to make their homes in trees roughed up or knocked over by browsing elephants.
(Dina Fine Maron. “Under poaching pressure, elephants are evolving to lose their tusks.” National Geographic. November 09, 2018.)
"This is an example of how human activity is changing the evolutionary trajectory of species all across the tree of life," Campbell-Staton said, adding, "humans are the most influential evolutionary pressure in history besides the five major mass extinction events."
(Aylin Woodward. “Poaching Has Caused 'Rapid Evolution' of Tuskless Elephants, New Study Reveals.” Business Insider. October 21, 2021.)
According to Kiyoko Gotanda, an evolutionary biologist at Brock University, Campbell-Staton’s team has “done a convincing job showing that the Gorongosa elephants have evolved in response to poaching,”
Usually, evolution is a slow process, but it can proceed with blinding speed. Hawaiian crickets went from noisy to silent in just 20 generations to avoid a lethal parasitic fly that was eavesdropping on their calls. The anole lizards that Campbell-Staton usually studies ended up with bigger toes and a tighter grip after hurricanes Irma and Maria battered the Caribbean, and better tolerance for cold after a polar vortex hit Texas. But almost all of these examples involved small creatures that breed quickly.
To see tusklessness evolving after just 15 years of war, in a “long-lived, slow-reproducing species like the elephant, is incredible,” says John Poulsen, a tropical ecologist at Duke University.
Ed Yong, staff writer at The Atlantic concludes …
“Campbell-Staton and his team are now planning to study the consequences of tusklessness … They hope to complete the full story of Gorongosa’s tuskless elephants – a tale in which the economic forces that dictate the price of ivory and the political history that drives a country to war collide upon a handful of genes in a single charismatic species, in a way that could reshape an entire ecosystem in the space of a few decades.”
(Ed Yong. “African Elephants Evolved Tusklessness Amazingly Fast.” The Atlantic. October 21, 2021.)
From a spot on the horizon, like brown lumps,
They come, throwing up the dust, and one can see that,
So as not to stray from the straightest path,
They make the distant dunes slip down under their broad and firm feet.
He who leads the way is an old chieftain. His body
Is covered with cracks like a tree-trunk gnawed and consumed by the weather.
His head is like rock, and the curve of his spine
Arches powerfully with his slightest effort.
Never slowing and not halting his march,
He guides his dusty companions to the certain goal;
And, leaving a ploughed sandy furrow behind them,
The enormous pilgrims follow their patriarch.
With ears spread like fans, their trunks between their teeth,
They make their way with eyes closed. Their bellies throb and steam,
And their sweat rises in the flaming air like a mist;
And a thousand glowing insects hum all around.
What do they care for thirst and the consuming fly,
And the sun baking their black and wrinkled skin?
They march on dreaming of the forsaken land,
Of the forests of sycamore-figs where their breed sheltered.
They will see again the river broken forth from the great heights,
Where the huge hippopotamus swims along bellowing,
Where, turned white by the moonlight and casting forward their shadows,
They would crush the reeds going down to drink.
Also, full of courage and deliberation, they pass on
Like a black line, in the endless sands;
And the desert resumes its stillness,
As the ponderous travellers fade on the horizon.
From “The Elephants” by Leconte de Lisle
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