Elephants without tusks evolve rapidly because of ivory poachers – .

Elephants without tusks evolve rapidly because of ivory poachers – .

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A large set of tusks is generally an advantage for elephants, allowing them to dig for water, bark for food, and play with other elephants. But during episodes of intense ivory poaching, these large incisors become a handicap.
Now researchers have highlighted how years of civil war and poaching in Mozambique have led to a greater proportion of elephants that will never develop tusks.

During the 1977-1992 conflict, fighters on both sides slaughtered elephants for ivory in order to fund war efforts. In the area that is now Gorongosa National Park, around 90% of the elephants have been killed.

A shipment of African ivory seized in 2013 is on display prior to its destruction in Colombo, Sri Lanka on January 26, 2016. The ivory has been traced to northern Mozambique and Tanzania and has been assessed by Sri Lankan customs. Lankans at 368 million rupees (over US $ 2.5 million at the time). (Eranga Jayawardena/The Associated Press)

The survivors were likely to share a key characteristic: half of the females were naturally defenseless – they simply never developed tusks – while before the war, less than a fifth had no tusks.

Like eye color in humans, genes are responsible for elephants inheriting tusks from their parents. Although the absence of tusks was once rare in African savannah elephants, it has become more common – as a rare eye color that is becoming widespread.

After the war, elephants had more female offspring, half of them defenseless

After the war, these helpless surviving females passed on their genes with expected but also surprising results. About half of their daughters were helpless. More puzzled, two-thirds of their offspring were females.

The years of unrest “changed the evolutionary trajectory of this population,” said evolutionary biologist Shane Campbell-Staton, based at Princeton University.

With colleagues, he worked to understand how the pressure of the ivory trade had tipped the balance of natural selection. Their findings were published Thursday in the journal Science.

A defenseless elephant matriarch walks with her two calves in Gorongosa National Park in Mozambique. As a result of an ivory-funded war, half of the females were born helpless. (ElephantVoices/The Associated Press)

Researchers in Mozambique, including biologists Dominique Gonçalves and Joyce Poole, observed the approximately 800 elephants in the national park for several years to create a catalog of mothers and offspring.

“Female calves stay close to their mothers, as do males until a certain age,” said Poole, scientific director and co-founder of the nonprofit ElephantVoices.

Gene suspected on the X chromosome

Poole had previously seen other cases of elephant populations with disproportionate numbers of defenseless females after intense poaching, notably in Uganda, Tanzania and Kenya.

“I wonder why it’s the females that have been defenseless for such a long time,” said Poole, co-author of the study.

In Gorongosa, the team collected blood samples from seven tusked female elephants and 11 helpless elephants, then analyzed their DNA for differences.

The elephant survey data gave them an idea of ​​where to look: because the helpless elephants were females, they focused on the X chromosome. (Women have two X chromosomes; men have one X chromosome and one Y chromosome.)

They also suspected that the affected gene was dominant – meaning that a female only needs one altered gene to become defenseless – and that when passed to male embryos, it can bypass their development.

“When mothers pass it on, we think sons probably die early in development, miscarriage,” said Brian Arnold, co-author and evolutionary biologist at Princeton.

Their genetic analysis revealed two key pieces of elephant DNA that they believe play a role in transmitting the defenseless trait. The same genes are associated with the development of teeth in other mammals.

“They produced compelling evidence for the genetic changes,” said Chris Darimont, conservation scientist at the University of Victoria in Canada, who was not involved in the research. The work “helps scientists and the public to understand how our society can have a major influence on the evolution of other forms of life.”

Most people think of evolution to be slow, but humans can step on the accelerator.

“When we think of natural selection, we think it takes place over hundreds, if not thousands of years,” said Samuel Wasser, a conservation biologist at the University of Washington, who was not involved. in the search. “The fact that this dramatic selection for defenselessness occurred over 15 years is one of the most astonishing findings. “

Now scientists are studying what defenseless elephants mean to the species and its savannah environment. Their preliminary analysis of fecal samples suggests that Gorongosa elephants modify their diet, without long incisors to peel bark from trees.

“The helpless females ate mostly grass, while the tusked animals ate more legumes and leathery woody plants,” said Robert Pringle, co-author and biologist at Princeton University. “These changes will last for at least several generations of elephants. “

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