WASHINGTON (AP) – 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.
The survivors were likely to share one 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, 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.
Researchers in Mozambique, including biologists Dominique GonÃ§alves and Joyce Poole, observed the approximately 800 elephants in the national park for several years to create a catalog of mothers and offspring.
âFemale calves stay close to their mothers, as do males until a certain age,â said Poole, scientific director and co-founder of the nonprofit ElephantVoices.
Poole had previously seen other cases of elephant populations with disproportionate numbers of defenseless females after intense poaching, notably in Uganda, Tanzania and Kenya. âI wonder why it’s the females that haven’t had tusks for a very long time,â said Poole, co-author of the study.
In Gorongosa, the team collected blood samples from seven female elephants with tusks and 11 female elephants without tusks, and then analyzed their DNA for differences.
The elephant survey data gave them an idea of ââwhere 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.
âWhen mothers pass it on, we think sons probably die early in development, a miscarriage,â 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, a 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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