Russell Millner/Alamy: A family of tuskless, elephants
Mozambique's female elephants quickly evolved to be tuskless after intense ivory poaching in the civil war. However, one mutation results in the death of male offspring.
Both sides hunted elephants to obtain ivory during the war. The Gorongosa National Park's elephant population plummeted from 1977 to 1992. An analysis of video footage from the past and current sightings of female elephants by Shane CampbellStaton of Princeton University and his collaborators has revealed that the percentage of tuskless males increased from 19 to 51% during the conflict. A statistical analysis showed that this is unlikely to have happened without selective pressure. Since the end of the war, the proportion of tuskless Elephants has been decreasing.
In many other countries, this same phenomenon has occurred. In Sri Lanka, for example, less than 5% of Asian male elephants have tusks.
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However, it is remarkable that all male African elephants have kept their tusks, despite being hunted. It appears that this is a genetic trait.
Although the team is still trying to find out what genetic mutations cause female tusklessness, they have found two. One of the mutations is likely to be in a gene called AMELX on the X-chromosome, which plays a role in tooth formation.
This mutation may also affect other important genes in the area. The X chromosome is two copies in a female. If one copy is not mutated, it will function normally and the elephant's health will be the same. This mutation can be fatal for males who inherit the X chromosome.
Campbell-Staton says that the same genetic condition can also occur in humans. It affects women who have it. The equivalent of tusks is missing in their upper lateral incisors. Male fetuses who inherit the mutation usually lose their lateral incisors in the third trimester.
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There is a possibility that genetic changes could be made to compensate for the lethality, and males may lose their tusks. There is no evidence that this will happen. Campbell-Staton says that even losing tusks to females can have many knock-on effects.
He says that tusks are essentially a Swiss army knife to African elephants. Campbell-Staton says they are used to remove bark from trees and dig holes for underground water or mineral. However, losing tusks can make it more difficult for females to survive other than poachers.
Many other animals also depend on tusked Elephants to obtain water from the holes dug using tusks. Campbell-Staton states that this is how biodiversity is maintained. These cascading effects can be quite unexpected and could result in our actions.
Journal reference: Science, DOI: 10.1126/science.abe7389
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