Feb. 6/2019

Feature:

Under poaching pressure, elephants are evolving to lose their tusks

“The oldest elephants wandering Mozambique’s Gorongosa National Park bear the indelible markings of the civil war that gripped the country for 15 years: Many are tuskless. They’re the lone survivors of a conflict that killed about 90% of these beleaguered animals…

Hunting gave elephants that didn’t grow tusks a biological advantage in Gorongosa. Recent figures suggest that about 1/3 of younger females—the generation born after the war ended in 1992—never developed tusks. Normally, tusklessness would occur only in about 2 to 4% of female African elephants.

Decades ago, some 4,000 elephants lived in Gorongosa, says Joyce Poole—an elephant behavior expert & National Geographic Explorer who studies the park’s pachyderms…as yet unpublished, research she’s compiled indicates that of the 200 known adult females, 51% of those that survived the war—animals 25 years or older—are tuskless. And 32% of the female elephants born since the war are tuskless.

A male elephant’s tusks are bigger & heavier than those of a female of the same age, says Poole, who serves as scientific director of a nonprofit called ElephantVoices…

This tuskless trend isn’t limited to Mozambique… In South Africa, the effect has been particularly extreme—fully 98% of the 174 females in Addo Elephant National Park were reportedly tuskless in the early 2000s.

‘The prevalence of tusklessness in Addo is truly remarkable & underscores the fact that high levels of poaching pressure can do more than just remove individuals from a population,’ says Ryan Long, a behavioral ecologist at the University of Idaho & a National Geographic Explorer…

Josephine Smit, who studies elephant behavior as a researcher with the Southern Tanzania Elephant Program, says that among the female elephants she tracks at Ruaha National Park, an area that was heavily poached in the 1970s & 1980s, 21% of females older than 5 are tuskless…

IMPLICATIONS OF TUSKLESSNESS

…elephants missing their tusks are surviving & appear healthy…Scientists say that the significant proportion of elephants with this handicap may be altering how individuals & their broader communities behave…

Tusks are essentially overgrown teeth. Yet they’re typically used for most tasks of daily living: digging for water or vital minerals in the ground, debarking trees to secure fibrous food, & helping males compete for females.

The work elephants do with their tusks is vital for other animals too. Elephants’ ‘role as a keystone species to topple trees & dig holes to access water is important for a variety of lower species that depend on them,’… Tusk action also helps create habitats…

If elephants are changing where they live, how quickly they move, or where they go, it could have larger implications for the ecosystems around them…

Now, Long & a team of ecology & genetic researchers are starting to study how tuskless elephants are navigating their lives. In June, the team started tracking 6 adult females in Gorongosa—half with tusks, half not—from 3 different breeding herds…

Their goal is to uncover more information about how these animals move, eat, & what their genomes look like. Long hopes to detail how elephants without the benefit of tusks as tools may alter their behavior to get access to nutrients. Rob Pringle, at Princeton University, plans to look at dung samples for insights about both diet & the army of microbes & parasites that live inside each elephant’s gut. Another collaborator, Shane Campbell-Staton, an evolutionary biologist at the University of California Los Angeles, will study blood, searching for answers about how genetics influences the phenomenon of tusklessness.

Exactly how this trait is inherited is ‘puzzling,’ Campbell-Staton says. Tusklessness does seem to occur disproportionately among females. It makes sense that tuskless males wouldn’t be able to compete for breeding access to female elephants, he says…

WORK-AROUNDS

‘I’ve observed tuskless elephants feeding on bark, & they’re able to strip bark with their trunks, & sometimes they use their teeth.’ They may also be relying on other elephants’ inadvertent help… Perhaps the elephants are targeting different kinds of trees that are easier to strip, or trees that have already had some stripping by other elephants—giving them a prepared leverage point for tearing off bark…

‘If you look at Asian elephants, females don’t have tusks at all, & depending on which population you look at in which country, most males are also often tuskless,’ Poole explains. Exactly why the Asian & African elephant populations have such different rates of tusklessness remains unexplained.

Yet Poole & others note that in areas in Asia that historically have been targeted for ivory hunts, tuskless levels are high—just as in Africa—underscoring that humans are leaving a lasting mark on Earth’s largest land mammal.”

Dina Fine Maron

nationalgeographic.com

Nov. 9/2018

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