Female Elephants Are Evolving Without Tusks in Mozambique

Scientists have linked heavy ivory poaching to an increase of tuskless African female elephants in Mozambique at the Gorongosa National Park, reports Maite Fernández Simon for the Washington Post. The East African country underwent a nearly two decade civil war that decimated 90 percent of the Grongosa elephant population because both sides engaged in animal poaching. This activity may have set off an evolutionary response that favored tuskless elephants as population numbers recovered. While no longer having ivory tusks may save elephants from poaching, the genetic mutation responsible for eliminating tusks is lethal to male elephants, reports Elizabeth Preston for the New York Times. Details of the study were published this month in the research journal Science.  

Ivory tusks are massive teeth or incisors that elephants use to dig for water, strip trees of bark for food, lift objects, protect their trunks, and defend themselves, reports Christina Larson for the Associated Press. The large teeth are highly sought after for their value. One pound of ivory is worth $1,500, and tusks can weigh up to 250 pounds.

Poaching was amplified during the Mozambican Civil War between 1977 to 1992 to finance the war efforts. Elephant population numbers dropped from 2,500 individuals to around 200 in the early 2000s, reports Nicola Jones for Nature. However, many female elephants that survived poaching during wartime were overlooked because they were already naturally tuskless. So, after the war ended, female elephants that naturally lacked tusks were more likely to pass down genes coding for tusklessness, per the New York Times.

To see how the ivory trade and poaching pressures may have amplified natural selection towards tuskless elephants, researchers started collecting data on the elephants at Gorongosa National Park. However, they noticed that the elephants with no incisors were usually female. The park has never seen a tuskless male, suggesting the trait related to tusklessness is sex-linked.

This find suggests the mutation for tusklessness may kill male elephants, per the New York Times. The team calculated that 18.5 percent of female elephants did not have tusks before the war began. After the war, 33 percent of 91 female elephants born were naturally tuskless, per Nature. Half of the female elephants at Gorongosa are tuskless, suggesting that poaching survivors passed the trait down to their daughters.

If a female elephant had one copy of the tuskless mutation, they would have no tusks. So, when the elephant reproduces, half of their daughters will have tusks, and the others will not have tusks at all. Half of the males will have tusks if their offspring is male, and the other half will die, possibly even before birth, per the New York Times.

“When mothers pass it on, we think the sons likely die early in development, a miscarriage,” says study co-author Brian Arnold, a Princeton evolutionary biologist, to the Associated Press.

By sequencing the genomes of seven females with tusks and 11 females without tusks, the research team identified two genes responsible for helping build tusks that may be causing tuskless females and death in tuskless males. One of the genes, called AMELX, is exclusively located on the X chromosome, and the other is called MEP1a, Nature reports. In mammals, these genes code for the development of incisor teeth.

AMELX is located near critical genes that can kill males if they are not present in the X chromosome, per the New York Times. Scientists are still not sure which changes are causing a loss of tusks in either of the genes, whichthey plan to evaluate in future research.  

“They have this very compelling genomic data,” Chris Darimont, a conservation expert at the University of Victoria, Canada, tells Nature. “This is a wake-up call in terms of coming to grips with humans as a dominant evolutionary force on the planet.”

Elizabeth Gamillo | | READ MORE

Elizabeth Gamillo is a correspondent for Smithsonian and a science journalist based in Milwaukee, Wisconsin. She has written for Science magazine as their 2018 AAAS Diverse Voices in Science Journalism Intern.