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Small, Isolated Elephants Follow Own Evolutionary Path
September 30, 2003
By MARK DERR
The small Borneo elephant represents the last remnant of an
ancient lineage, a team of international biologists has
determined. The finding, based on DNA samples, overturns a
long-held prevailing theory of the animals' origins: that
they were descended from domesticated elephants that
reverted to the wild.
Instead, the elephant, isolated in the tropical rain
forests of northeastern Borneo, has followed an independent
evolutionary path for at least 18,000 years, and probably
longer, the scientists conclude. In the process, it has
become genetically distinct from other Asian elephants, the
experts say, based on extensive comparisons of elephant DNA
obtained across Asia.
The report appears in the October issue of The Public
Library of Science, Biology, a new peer-reviewed, online
journal that was created as a free alternative to
established journals that allow access only to subscribers.
(Their paper was posted in advance of its publication at
biology .plosjournals.org.)
The analysis also revealed that the current Borneo elephant
population, estimated at 1,000 to 2,500, lacks genetic
variation, an indication that it arose from a small number
of founders, was never very numerous and is highly inbred,
said Dr. Prithiviraj Fernando, the main author and a
scientist at the Columbia University Center for
Environmental Research and Conservation.
The researchers eventually hope to learn whether the Borneo
elephant - smaller than others in Asia and more
round-bodied, with larger ears and straighter tusks - is
trapped in a genetic bottleneck, caused by extensive
inbreeding, or has already passed through it, as some
evidence suggests, Dr. Fernando said in a telephone
interview from Sri Lanka.
Extensive inbreeding can lead to undesirable genetic
variants that leave the animals vulnerable to defects,
diseases and changes in their environment, said Dr. Don J.
Melnick, director of the Columbia center and a co-author of
the study. Populations in bottlenecks often go extinct, he
said.
Dr. Raman Sukumar, chairman of the World Conservation
Union's Asian Elephant Specialist Group, said in an e-mail
message, "This paper is indeed very significant in that it
demonstrates a certain genetic uniqueness for the elephants
of Borneo, and the most likely explanation is that the
elephant colonized the island during the Pleistocene and
has evolved there independently." He was not involved in
the research.
Under the prevailing theory, the Borneo elephants descended
from Indian elephants presented to the Sultan of Sulu in
1750 by the East India Trading Company or were among a
group shipped from Sumatra around the same time, when
elephants were being heavily traded for war, logging and
ceremonies from the 16th through the 18th century.
A few of those elephants were believed to have escaped or
been released and reverted to the wild, while retaining the
tameness of their domesticated forebears.
Asian and African elephants will attack and kill humans who
threaten them, but the Borneo elephants are not aggressive
toward people, said Dr. Michael Stuewe, a co-author of the
paper affiliated with the Asian Rhino and Elephant Action
Strategy of the World Wildlife Fund.
"I've seen researchers literally go up and touch them," he
said. "That tameness gave people the idea that they were
zoo animals and not worth special attention."
The elephants are found only in northeastern Borneo, in the
Malaysian province of Sabah and in the Indonesian province
of Kalimantan, where their forest habitat is to be
protected in a park, Dr. Stuewe said. But in Sabah, logging
and the conversion of forests to palm oil plantations and
acacia farms for wood pulp represent a significant threat.
When the World Wildlife Fund became involved in 1999 in
efforts to preserve the jungles of Sabah, "we had to prove
that we weren't wasting money on zoo animals," Dr. Stuewe
said.
Biologists with the agency began collecting dung and blood
samples from wild and captive elephants throughout Asia and
shipping them to the researchers in New York.
There Dr. Fernando and his colleagues extracted and
analyzed mitochondrial and autosomal DNA. Mitochondrial
DNA, involved in the cell's energy system, is inherited
from the mother; autosomal DNA is inherited from both
parents.
Asian and African elephants and mammoths diverged from a
common ancestor about six million years ago. Asian
elephants ranged from the Tigris and Euphrates Rivers into
China and Borneo.
Dr. Fernando had previously shown that the Asian elephant
then split into two main lineages some three million years
ago.
In this case, lineages reflect variations in mitochondrial
DNA, dated through a genetic clock based on the rate of
naturally occurring mutation.
Most mainland Asian elephants of today have diverged from
the "alpha" lineage identified by Dr. Fernando. The
elephants on the islands of Sumatra and Borneo and on the
Malay Peninsula branched from the "beta" lineage. For
reasons Dr. Fernando is now studying, Sri Lanka has
elephants of both lineages.
The most recent survey shows that Borneo elephants diverged
from the beta lineage 300,000 years ago. The researchers
had more difficulty putting a date on their colonization of
Borneo.
The lack of evidence of elephants anywhere on Borneo other
than the northeast end, or of Borneo elephants anywhere
else in Asia, adds to the mystery surrounding the animals'
arrival and isolation.
Dr. Melnick suggested that the Borneo elephant could have
diverged in its current home range and never left, the way
the elephants of Sumatra and the Malay Peninsula appear to
have done at a later date.
Or the lineage could have originated on the mainland, with
part or all of it subsequently migrating to Borneo, as sea
levels rose and fell during the Pleistocene with the
advance and retreat of vast ice sheets, Dr. Fernando said.
When seas were low, the Malay Peninsula and Borneo,
Sumatra, Java and Bali formed a landmass called Sundaland.
The scientists suggest that the elephants crossed into
Borneo during one of those periods, but not since 16,000
B.C. at the peak of an ice age.
Since the glaciers melted around 10,000 B.C., the elephants
have been stuck on their island. Several researchers,
however, suggest that their genetic isolation began long
before that.
While a number of conservation organizations have seized on
the research and have begun calling the Borneo elephant a
distinct subspecies, the authors reject that approach for
now. "A subspecies is difficult to define because it is
subjective," Dr. Fernando said.
An attempt in the 1950's to classify the elephant as
Elephas maximus borneensis faltered because of problems
with the morphological work involving comparisons of the
skeleton and other physical characteristics like tusks, Dr.
Fernando said.
Until more extensive morphological and genetic studies are
completed, the researchers have opted to apply the
designation E.S.U., evolutionary significant unit, a
reproductively isolated population that is important to the
species' evolution.
By whatever name, the little Borneo elephant has suddenly
been transformed from a feral animal of dubious origin to
an ancient beast following its own evolutionary path in
splendid isolation. The imperative for preserving it has
risen accordingly.
"The Borneo elephant obviously needs special attention, and
this is all the more imperative in view of the ongoing
rapid attrition of its Sabah range," Dr. Sukumar said.
Dr. Melnick added, "The elephants of Borneo are only going
to get more different genetically if they are properly
protected and managed."
http://www.nytimes.com/2003/09/30/science/30ELEP.html?ex=1065970639&ei=1&en=347223dc852ff686
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