An elephant’s teeth are among its defining characteristics – they help the animal lift heavy branches, fell trees, strip bark, fight and dig holes for water and minerals.

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But a growing proportion of female elephants in Mozambique’s Gorongosa National Park are born without these vital tools, and scientists say it is a evolutionary response brutal killing of elephants For his ivory tusks during the country’s 15-year civil war.

Elephant experts working in the park began to notice this phenomenon after the war ended in 1992. Field data and analysis of old video footage of the park found that the proportion of female elephants without teeth increased more than three-fold between 1972 and 2000. There was a period during which the elephant population dropped from about 2,000 to about 250 individuals, said Ryan Long, an associate professor of wildlife science at the University of Idaho.

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“During the war, Gorongosa was essentially the geographic center of the conflict,” Long said via email. “As a result, there were a large number of soldiers in the area and a lot of allied motivation … to kill the elephants and sell the ivory to buy arms and ammunition. The resulting level of poaching was very intense.”

genetic signature

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Scientists now have a better understanding of the genetic basis of toothlessness and why it affects only female elephants, according to a study published Thursday in the journal Science.

The analysis showed that women without teeth were five times more likely to survive during the 28-year period, so adaptation was unlikely to stand a chance.

Predation occurs naturally – and only in females – even in the absence of poaching, but usually only in a small number of elephants. In Gorongosa in the 1970s, 18.5% of female elephants did not have teeth, compared to 51% three decades later.

Long, an author of the study, said, “Evolution is a change in genetic characteristics within a population over successive generations, and based on the results of our study, the shift toward tusklessness among female elephants in Gorongosa fits this definition perfectly.” “

“The fact that it happened so rapidly is really rare, and a direct function of the strength of the selection,” he said via email. “In other words, it happened so quickly because tuskless women were much more likely to survive the war, and thus much more likely to pass their genes on to the next generation.”

But what about male elephants? After taking blood samples from 18 toothless and toothless female elephants, the researchers sequenced their genomes. They found that women without teeth have genetic variation in a very specific region of the X-chromosome, which plays a role in the development of tusks.

“Women have 2 X chromosomes. In women without teeth, one of those chromosomes is ‘normal’ and the other contains the deleted information,” Long Explained.

“When a toothless female conceives a male offspring, that male has a 50/50 shot of receiving the affected X-chromosome from its mother. If she receives a ‘normal’ chromosome she will survive Tusks will remain and will be born with the necessary genetic information.”

However, if a male elephant embryo receives the chromosome with the genetic variant, it dies in the womb because the way the female is born is lethal to the male, Long said.

According to the study, the exact genetic and developmental mechanism of tooth loss in females and loss of male elephants during the 22-month pregnancy of elephants is not yet understood.

Long said the number of elephants in Gorongosa has grown to about 800. Not having teeth doesn’t pose a significant deterrent to female elephants, but it’s something researchers want to study further. He said that dietary analysis shows that women without teeth eat more grass.

“The population is doing well and there are a lot of toothless elephants. They have apparently adapted to life without teeth, but there’s a lot we don’t know.”