Poachers, war may have led to elephants not having tusks
A deep-enough wound will leave a scar, but a traumatic event in the history of an animal population may leave a mark on the genome itself. During the Mozambican Civil War (1977-92), humans killed so many elephants for their lucrative ivory that the animals seem to have evolved in the space of a generation. The result: A large number are now naturally tuskless.
A paper published Thursday in Science has revealed the tooth-building genes that are probably involved. One of those same genes is linked to a syndrome in human females that causes abnormal tooth growth. In both humans and elephants, the mutation is lethal to males.
Although evolving to be tuskless might spare some surviving elephants from poachers, there will probably be long-term consequences for the population.
Normally, both male and female African elephants have tusks, which are really a pair of massive teeth. But a few are born without them. Under heavy poaching, those few elephants without ivory are more likely to pass on their genes. Researchers have seen this phenomenon in Mozambique’s Gorongosa
National Park, where tuskless elephants are now a common sight.
Female elephants, that is. What no one has seen in the park is a tuskless male.
“We had an inkling” that whatever genetic mutation took away these elephants’ tusks was also killing males, said Shane Campbell-Staton, a biologist at Princeton University
To learn more, Campbell-Staton and his co-authors started with longterm data, including prewar video footage of Gorongosa’s elephants.
They calculated that even before the war, nearly 1 in 5 females were tuskless. This might reflect earlier conflict and poaching pressure, Campbell-Staton said. In well-protected elephant populations, tusklessness can be as low as
2%.
Today, half of Gorongosa’s females are tuskless. The females who survived the war are passing the trait on to their daughters. Mathematical modeling showed this change was almost certainly because of natural selection and not a random fluke. In the decades spanning the war, tuskless females had more than five times greater odds of survival.
And the pattern of tusklessness in families confirmed the scientists’ hunch: It seems to be a dominant trait, carried by females, that is lethal to males.
That means a female with one copy of the tuskless mutation has no tusks. Half of her daughters will have tusks, and half will be tuskless.