A massive set of tusks is often an advantage for elephants, allowing them to dig up water, get tree bark for food, and play with other elephants. But during intense ivory po.ac.hing, those large incisors became a thing to suffer.
Now, researchers have pinpointed how years of civil war and po.a.ching in Mozambique have led to a greater proportion of elephants never developing larger tusks.
During the conflict from 1977 to 1992, fig.hte.rs on both sides slau.gh.tered elephants for their tusks to finance the w.a.r efforts. In the area that is now Gorongosa National Park, about 90% of elephants were k.il.ed.
Survivors were shared one key feature: half of the females naturally had no tusks – they simply never developed tusks – while before the war, less than a fifth lacked tusks.
Like eye color in humans, genes are responsible for whether elephants inherit tusks from their parents. While the African wild elephant was once rare, it’s growing in popularity – just as rare eye colors are becoming common.
After the w.a.r, that tuskless surviving passed on their genes with expected, as well as surprising, results. About half of their daughters have no tusks. More confusingly, two-thirds of their children were female.
Evolutionary biologist Shane Campbell-Staton, based at Princeton University, said the years of instability had “changed the trajectory of evolution in that population”.
With colleagues, he explored how the pressures of the ivory trade had impacted the scale of natural selection. Their findings were published Thursday in the journal Science.
Researchers in Mozambique, including biologists Dominique Goncalves and Joyce Poole, observed about 800 of the park’s elephants over several years to create a catalog of mothers and offspring.
“The female calves stay with their mothers, and so do the males until a certain age,” said Poole, chief scientific director and co-founder of the nonprofit ElephantVoices.
Poole has previously seen other cases of elephant populations with disproportionately large numbers of tuskless females following intense po.ac.hing, including in Uganda, Tanzania, and Kenya. Poole, the co-author of the study, said: “I didn’t understand why the females are tuskless for a long time.”
In Gorongosa, the team collected blood samples from seven female elephants with tusks and 11 tuskless female elephants and then analyzed their DNA to find the differences.
Elephant survey data gave them an idea of where to look: Since elephants don’t have tusks as females, they focus on the X chromosome. (Females have two X chromosomes; males have one X and a Y chromosome.)
They also suspected that the gene involved was dominant – meaning females only need one gene to be altered to become tuskless – and when passed to male embryos, it could short-circuit their development.
Brian Arnold, co-author and an evolutionary biologist at Princeton, said: “When mothers pass it on, we think the boys may d.i.e early in development, a miscarriage.
Their genetic analysis revealed two key parts of the elephant’s DNA that they believe play a role in passing on the trait of tusklessness. Similar genes are involved in teeth development in other mammals.
“They showed evidence of gun smoking for genetic changes,” said Chris Darimont, a conservation scientist at the University of Victoria in Canada who was not involved in the study. The work “helps scientists and the public understand how our society can have a major influence on the evolution of other life forms.”
Most people think of evolution as something that happens slowly, but humans can speed things up.
Samuel Wasser, a conservation biologist at the University of Washington who was not involved in the study, said: “When we think about natural selection, we think about it happening in the hundreds, or thousands, of years. “The fact that the dramatic choice to be ivory-free has occurred for more than 15 years is one of the most astonishing findings.”
Now scientists are studying what tuskless elephants mean for the species and its savannah environment. Their preliminary analysis of fecal samples showed that the Gorongosa elephants were changing their diet without the long front teeth to peel bark from trees.
“The tuskless females eat mostly grass, while the tusks eat more beans and more legumes and tough woody plants,” said Robert Pringle, co-author and biologist at Princeton University.” These changes will last for at least several generations of elephants.”