A serious enough cut will leave a scar, but a traumatic event in the history of an animal community may leave an imprint on the DNA of the animal population as a whole, as well. In the decades between 1977 and 1992, humans slaughtered so many elephants for their profitable ivory that the creatures appear to have evolved in the span of a generation. The Mozambican Civil War lasted from 1977 to 1992. In the end, many of them have lost their tusks due to natural selection.
In a report published Thursday in Science, researchers identified the tooth-building genes most likely responsible for the condition. In addition, an abnormal tooth growth syndrome in females caused by one of those same genes has been related to one of those genes. Males in both humans and elephants are killed by the mutation, which is present in both species.
Although the evolution of trustlessness may protect some remaining elephants from poachers in the short term, there will almost certainly be long-term ramifications for the population.
The tusks of an African elephant are a pair of huge teeth, and they are typically found on both male and female elephants. However, a few people are born without them. Under conditions of widespread poaching, those few elephants who do not have ivory are more likely to pass on their genes to their offspring. According to researchers who have observed the phenomena, elephants without tusks are becoming a common sight in Mozambique’s Gorongosa National Park.
That is female elephants, to be precise. What no one has seen in the park is a male lion with no tusks.
“We had a sneaking suspicion,” said Shane Campbell-Staton, an evolutionary scientist at Princeton University, that whatever genetic mutation was responsible for the elephants’ tusk loss was also responsible for the elephants’ deaths as men.
Dr. Campbell-Staton and his co-authors started with long-term data, including prewar film footage of the Gorongosa’s elephants. This allowed them to understand more about the elephants.
They calculated that approximately one in every five females was born without tusks even before the war. Dr. Campbell-Staton speculated that this could be a result of past conflict and poaching pressure. Tusklessness can be as low as 2 percent in elephant populations that have been well-protected.
Half of the females on Gorongosa are now tuskless, as in most other African countries. The trait is being passed on to the next generation by the female survivors of the war. Natural selection, rather than chance, was virtually certainly responsible for this modification, according to mathematical modeling findings. Females born without tusks had more than five times the chance of surviving during the decades’ preceding World War II.
The pattern of tusklessness in families further corroborated it: it appears to be a dominant trait, carried by females, that is fatal to males. That means that a female who carries one copy of the tuskless mutation will be devoid of tusks. As a result, half of her daughters will be born with tusks, and the other half will be born without tusks. However, half of her sons will be born with tusks, while the other half will perish, maybe before they are born.
They sequenced the genomes of 11 females born without tusks and seven females born with tusks, looking for variations between the two groups. Researchers looked for regions of the genome that showed the signature of recent natural selection rather than the random DNA reshuffling that occurs over time as part of evolution. They discovered two genes that appeared to be involved.
Both genes contribute to the development of teeth. However, the gene named AMELX, which is found on the X chromosome, as predicted by the research team, best explains the patterns observed in nature. Interestingly, the gene is also implicated in a rare human disease resulting in females having undersized or deformed teeth — particularly the top teeth between the front teeth and canines, which are anatomically similar to an elephant’s tusks. In addition to females, males are killed by the human syndrome, which is caused by a missing block of DNA that comprises the tooth gene and other critical genes in the vicinity.
“We don’t know what the particular modifications are that are driving this loss of tusks in either one of those genes,” Dr. Campbell-Staton says of the elephant genome’s tusk-loss genes. However, that’s one of the things the experts are hoping to figure out in the near future as well.
They also want to know what it’s like to be a tuskless elephant and their daily routine. In their natural habitat, elephants use their tusks to remove tree bark for food, dig water holes, and defend themselves. In the absence of this critical tool, how will you be forced to change your behavior to make up for a lost time? Dr. Campbell-Staton made the statement.
Furthermore, Dr. Campbell-Staton believes that the rise in trustlessness may impact not only individual elephants but also the entire population because fewer males are being born.
It’s a “really elegant work,” said Fanie Pelletier, a population biologist at the Université de Sherbrooke in Quebec who was not involved in the research but contributed to an accompanying piece in Science. “I believe it’s a very nice study,” she added. “It’s also a really thorough story,” says the author. “All of the parts are in place,” she stated.
Dr. Pelletier has conducted her research on bighorn sheep in Canada, which she has published. As prize hunters sought out the males with the largest horns, the sheep developed to have lesser horns to avoid being targeted.
She claims that the shift in sheep is mild, in contrast to the elephants’ complete loss of tusks. And, according to Dr. Pelletier, the elephants’ genetic alteration has exacerbated their difficulties. Even if poaching were to cease tomorrow, trustlessness would continue to kill males indirectly, and it could take a long time for the prevalence of this feature to return to normal levels.
Dr. Campbell-Staton acknowledged that, even though elephants have evolved to be more resistant to poachers, this is hardly a case of “success.”
It’s easy, he believes, to come away from hearing stories like these with the impression that “all is good,” that “they have developed and are now better and can deal with it.” However, the reality is that species pay the price for undergoing rapid evolution.
According to him, “selection usually comes at the expense of life,” and he went on to explain why.
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