Tuskless elephants became common as an evolutionary response to poachers

When ivory poachers target elephants, the hunters can affect more than just animal numbers. In Mozambique, past hunting pressure led to an increase of naturally tuskless elephants in one park, a study finds. 

During the Mozambican Civil War, which lasted from 1977 to 1992, armies hunted elephants and other wildlife for food and ivory (SN: 5/5/19). This caused the number of large herbivores to drop more than 90 percent in the country’s Gorongosa National Park. 

Now, video footage and photographic records show that as elephant numbers plummeted, the proportion of tuskless female African savanna elephants (Loxodonta africana) rose from about 18 percent to 51 percent.

Decades of poaching appear to have made tusklessness more advantageous from an evolution standpoint in Gorongosa, encouraging the proliferation of tuskless females with mutations in two tooth genes, researchers report in the Oct. 22 Science.

The rapid culling of tusked individuals changed the makeup of traits in the elephant population in only two decades, leaving behind more tuskless individuals, say evolutionary biologist Shane Campbell-Staton of Princeton University and colleagues. The tuskless trait is heritable, and the evolutionary change in the population may stick around for several generations at least, even as poaching eases.

The team also analyzed the genetic instruction books of 18 tusked and tuskless females, zeroing in on two genes rife with mutations in tuskless females. In humans, the disruption of one of those genes can cause tooth brittleness and the absence of a pair of upper incisors that are the “anatomical equivalent of tusks,” Campbell-Staton says. Abnormalities in the other gene’s protein product can cause malformations of the tooth root and tooth loss. 

Poaching “changing the course of evolution” in Gorongosa’s elephants, Campbell-Staton says, can have reverberating effects through the ecosystem given elephants’ dramatic impact on their surroundings. 

“[Tusks are] not just ornamental. They serve a purpose,” he says, detailing how elephants use tusks to dig for water and strip tree bark for food. “If an elephant doesn’t have the tool to do those things, then what happens?”