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yet unpublished, research she’s compiled indicates that of the 200 known adult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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