Losing Their Tusks

Tusks are essentially long teeth (see Elephant Anatomy). They come in handy for a variety of reasons. “Elephants use their tusks as tools,” says Joyce Poole, an elephant behaviorist in Gorongosa National Park. Both male and female elephants use tusks to dig holes to access water underground. They use them to break branches, or even uproot entire trees, and to strip off bark to eat. Males also use their tusks when battling with other males over potential female partners.

“There’s a strong selection for males to have big tusks, because those are their weapons when they fight,” says Poole. Selection is a process in which traits, such as the presence or absence of tusks, are gained or lost over time depending on whether they help members of a population survive or reproduce. These traits are passed on to offspring through units of hereditary material called genes. Battling for mates is an example of natural selection, where natural processes—rather than human activity—determine which traits an organism is born with.

Tusks are actually long teeth (see Elephant Anatomy). They come in handy for different reasons. “Elephants use their tusks as tools,” says Joyce Poole, an elephant behaviorist in Gorongosa National Park. Male and female elephants use tusks to dig holes. That’s how they reach water underground. They use them to break branches or even uproot whole trees. And their tusks help strip off bark for food. Males also use their tusks to fight with other males over females.

“There’s a strong selection for males to have big tusks, because those are their weapons when they fight,” says Poole. In the process of selection, traits are gained or lost over time. This depends on whether they help members of a population survive or reproduce. Having tusks and being tuskless are examples of traits. The traits are passed on to offspring through genes. These are units of hereditary material. Fighting for mates is an example of natural selection. That’s when an animal is born with traits because of natural processes, not human activity.

In the 1970s and 1980s, Mozambique endured a brutal civil war. “Gorongosa National Park was the site of many battles,” says Poole. “People shot elephants for food. And elephants were targeted for their tusks, which were sold to raise money for weapons,” she says. About 90 percent of the elephants in the park were slaughtered during those years.

Poaching created a powerful new form of selection affecting elephant survival and reproduction. “In a natural situation, it’s good to have tusks,” says wildlife biologist Ryan Long of the University of Idaho. “But in a situation with a lot of poaching, if you’re an elephant who has tusks, you may be more likely to get killed.”

In the 1970s and 1980s, Mozambique went through a terrible civil war. “Gorongosa National Park was the site of many battles,” says Poole. “People shot elephants for food. And elephants were targeted for their tusks, which were sold to raise money for weapons,” she says. About 90 percent of the elephants in the park were killed during those years.

Poaching created a powerful new form of selection. It affected elephant survival and reproduction. “In a natural situation, it’s good to have tusks,” says Ryan Long. He’s a wildlife biologist of the University of Idaho. “But in a situation with a lot of poaching, if you’re an elephant who has tusks, you may be more likely to get killed.”

That seems to be exactly what happened in Gorongosa during the war. Elephants with tusks died in huge numbers. Poachers killed off the oldest males first, since their tusks are largest. Then hunters set their sights on older females, with the next largest tusks. Sometimes they even killed young elephants for their little tusks.

When the conflict ended, more than half of the females who had survived were ones with no tusks (see Tusk Trends). And when those tuskless survivors had babies, many passed on the trait: About a third of females born after the war lack tusks. Male African elephants almost always have tusks, and that remained true after the war.

That’s what happened in Gorongosa during the war. Elephants with tusks died in huge numbers. Poachers killed off the oldest males first. That’s because their tusks are largest. Then hunters went after older females, with the next largest tusks. Sometimes they even killed young elephants for their little tusks.

The war finally ended. Some elephants had survived. But more than half of the living females were ones with no tusks (see Tusk Trends). And when those tuskless females had babies, many passed on the trait. About a third of females born after the war lack tusks. Male African elephants almost always have tusks. That stayed true after the war.

Poole, Long, and other scientists have many questions about tusklessness and how it affects elephants. One mystery concerns the heredity of the trait. Scientists don’t know which genes are responsible for it or what explains its pattern of inheritance: How is it that some females are born tuskless but males almost never are?

Another big question is how tusklessness affects elephants’ behavior and interactions with their ecosystem—the community of organisms interacting with their physical environment. Tuskless females appear healthy and survive as well as their tusked relatives. “We observe that they seem just fine, and we know that elephants use their tusks for all sorts of things,” says Long. “What are they doing differently that allows them to be successful without tusks?”

To find out, Long and his collaborators have launched a study comparing tusked and tuskless females in Gorongosa. They’re analyzing blood samples to understand the genetics of tusklessness. They’ve collected samples of dung, so they can compare the elephants’ diets. And they’ve put GPS tracking collars on the elephants to compare the animals’ movements.

Poole, Long, and other scientists have many questions about tusklessness and how it affects elephants. One mystery is how the trait is passed on. Scientists don’t know which genes cause it, and they can’t explain its pattern. Why are some females born tuskless, but males almost never are?

They’re looking at another big question: How does tusklessness affect elephants’ behavior and interactions with their ecosystem? That’s the community of living things in their physical environment. Tuskless females seem healthy. They survive as well as tusked elephants. “We observe that they seem just fine, and we know that elephants use their tusks for all sorts of things,” says Long. “What are they doing differently that allows them to be successful without tusks?”

To find out, Long and his team have started a study. It will compare tusked and tuskless females in Gorongosa. They’re looking at blood samples to understand the genes behind tusklessness. They’ve collected samples of dung. That way, they can compare the elephants’ diets. And they’ve put GPS tracking collars on the elephants to compare their movements.

Long is excited to study evolution in action. Evolution happens whenever there are changes in a population’s genes because of selection. “In these elephant populations, we’re seeing changes from artificial selection,” says Long. This type of selection was caused by the poachers in Gorongosa.

His investigation could help scientists understand a phenomenon that may ultimately affect many elephants across Africa. Increases in the number of tuskless elephants have been documented in South Africa, Uganda, and Tanzania. Although the herds in Gorongosa are now well protected and recovering from the losses they suffered during the war, Poole says, “many other populations are still declining.”

Long notes that tuskless elephants are a stark reminder of the human impact on these animals. “Everybody knows that poaching can lead to declining populations,” says Long, “but we’re only beginning to understand the effects it can have on the elephants who survive. Their populations may be altered for generations to come.”

Long is excited to study evolution in action. This happens when selection leads to changes in a population’s genes. “In these elephant populations, we’re seeing changes from artificial selection,” says Long. This type of selection was caused by the poachers in Gorongosa.

His study could help scientists understand the increase in tusklessness. In the end, this change may affect many elephants across Africa. Growing numbers of tuskless elephants have been found in South Africa, Uganda, and Tanzania. The herds in Gorongosa suffered great losses during the war. Now they’re well protected and recovering. But Poole says, “many other populations are still declining.”

Long says that tuskless elephants are an important reminder. They show how humans affect these animals. “Everybody knows that poaching can lead to declining populations,” says Long, “but we’re only beginning to understand the effects it can have on the elephants who survive. Their populations may be altered for generations to come.”