Malaysian Mystery Leopards|Richard_Ffirstname.lastname@example.org|04/24/07 at 13:30:19|richard_f|xx|0|126.96.36.199|Malaysian Mystery Leopards
By Fiona Sunquist
A new study reveals that the leopards of peninsular Malaysia are black
rather than the typical spotted gold, but the question remains: Why?
"Another black leopard," biologist Kae Kawanishi thought as she leafed
through pages of color prints just back from the processing lab.
Stacks of yellow-and-white albums filled with images covered the
surface of her tiny desk at her home in Kuala Lumpur, Malaysia, while
hundreds more albums filled with neatly labeled photos from previous
months' surveys lined a nearby bookshelf.
Kawanishi was in the last month of her three-year study of tigers in
peninsular Malaysia's Taman Negara National Park. Although the epic
camera-trapping study—in which she and her research team set up
cameras in the rain forest so that animals would trigger trip wires
and photograph themselves—was designed primarily to estimate tiger
density, Kawanishi's work also gave the world its first glimpse of the
full array of wildlife in a Southeast Asian lowland rain forest.
Kawanishi and her team, bankrolled largely by the Save the Tiger Fund
through the University of Florida's Malaysia Tiger Project, racked up
thousands of photos of Malaysian wildlife. Day and night, tigers,
tapirs, elephants and porcupines strolled past the 150 or so cameras
set along game trails. Dozens of little known species, including
clouded leopard, dhole, golden cat and the goatlike serow, tripped the
infrared sensors and photographed themselves. Among the most
unexpected finds was Taman Negara's leopards, which triggered the
cameras more than 100 times. The surprising thing about them: In every
one of the photos the big cats were black.
Looking for an explanation as to why this usually rare color phase
was prevalent, Kawanishi checked with the forest people that helped
her team with the camera-trapping study. "About 400 Orang Asli
[original people] live in the park," she explains. "They are
hunter-gatherers. They know every animal in the forest. When we asked
them about the various cats, they recognized clouded leopards, tigers
and black leopards, but no one recognized a large spotted cat. To the
Orang Asli all leopards are harimau kumbang, or black leopards." The
fact that the Orang Asli never saw spotted leopards at least proved
that the cameras were not lying.
Leopards—large, usually golden cats with black spots—range throughout
much of Africa, avoiding only desert areas, and across the Middle East
into Asia, including Java and Sri Lanka and extending as far north as
Siberia. They feed on creatures varying in size from rodents to hoofed
animals in excess of 200 pounds. Competing with lions or tigers in
parts of their habitat, they often drag their prey up into trees,
where larger cats and scavengers cannot get at it. An estimated
500,000 leopards survive worldwide, although some of the 22 recognized
subspecies are endangered. They range in weight from 60 to more than
Black leopards, also known as black panthers, are rare in the wild.
Almost never seen in Africa, they show up only occasionally in
southern India. Historical reports and hunters' stories from a century
ago record that as many as half of the leopards in the Malay Peninsula
may have been black, but as Kawanishi has just discovered, black
leopards now seem the norm in that part of the world. The reason might
be as simple as camouflage or as complex as disease resistance.
Just as albino individuals—all white with unpigmented, red eyes—crop
up occasionally in many species, so too do melanistic, or all-black,
individuals. The color comes from a pigment called melanin, the same
pigment responsible for suntans. Both albinism and melanism are
influenced by genes. In domestic cats and leopards, a single recessive
gene controls dark coat color, so both black and spotted leopard cubs
can occur in the same litter, and black cubs can be born to spotted
Black leopards have a reputation for being more aggressive than
spotted leopards, and early biologists thought they were a separate
species. Not so. "Black leopards are simply leopards with dark coats,"
says John Seidensticker, senior scientist at the National Zoo in
Washington, D.C. "If you look closely, you can see the faint outline
of spots in the black leopard's dark fur."
Black leopards are black because they have a mutation in the gene
responsible for coat color. But there is more to color than meets the
eye. Genetic mutations that affect coat color can have multiple
physical effects, influencing two or three seemingly unrelated
physical characteristics. Lack of pigment cells is implicated, for
example, in the deafness typical of white cats with blue eyes. A clue
to the link between pigment genetics and deafness lies in the fact
that white cats with one blue and one yellow eye are often deaf on the
side with the blue eye. Studies of lab mice suggest that pigment cells
are involved in maintaining fluid in ear canals. Without the fluid,
the canals collapse, causing deafness as the auditory nerves degenerate.
Similarly, the characteristic dark ears, nose color pattern and
crossed eyes of Siamese cats are all caused by the same gene. The gene
that causes defective "frizzle-trait," or curly, feathers in chickens
also decreases their egg laying and causes changes in their hearts and
kidneys. Recent research on mice has shown that a mutation in the gene
that produces yellow fur results in mice that are chronic overeaters,
while another mutation that produces white-spotted fur causes anemia
and sterility. Scientists are using mouse models to study the
processes that cause these conditions in humans.
In the natural world, rare genetic variations that occur in pigment
genes can help animals to adapt better to their habitats. These color
differences often provide a selective advantage through camouflage.
For example, a recent study of rock pocket mice in the deserts of
Arizona and New Mexico by Michael Nachman and his coworkers at the
University of Arizona found that pocket mice tend to match the ambient
color of their habitat—usually a light sandy color. However, in areas
where the mice live on dark, rocky lava flows, the rodents wear dark,
almost black fur. This camouflage presumably provides more protection
from great horned owls, a significant predator of these mice.
The adaptive benefits of black fur for leopards are more difficult to
interpret. Researchers Eduardo Eizirik, Stephen O'Brien and their
colleagues at the National Cancer Institute's Laboratory of Genomic
Diversity in Maryland have mapped, cloned and sequenced the genes
responsible for black coats in cats. "Melanism is particularly common
in the cat family," Eizirik says. "This is important because it means
that dark fur, or something connected with it, has a survival
benefit." One theory is that animals living in dark, humid forests
generally have darker fur for camouflage. African leopards spend most
of their lives in open habitats with dappled sunlight, where spots are
the best disguise. In Malaysian forests, black coats may be better
camouflage than spots. "The most likely benefit of melanism is
camouflage for hunting," Eizirik says.
However, the black leopard story may prove more complicated than mere
camouflage. O'Brien, chief of the Laboratory of Genomic Diversity,
suggests that there are many other selective pressures besides being
able to hide. "Another explanation is that about 70 percent of
selective pressures associated with the biological environment involve
microbes and diseases," O'Brien says. Recent studies have shown that
coat-color genes also affect the immune system. "The types of
receptors used for coat colors are also used by viruses to enter
cells," O'Brien says. "It is plausible that some of these color
mutations are adaptive—relics of historic epidemics."
The fossil record indicates that leopards have roamed in peninsular
Malaysia for more than 150,000 years. The first to arrive there must
have been spotted, like their relatives in Africa and Asia. Over time,
spotted coats gave way to black, as Kae Kawanishi's snapshots show. It
might be that the black coats arose as an immune system response to an
ancient epidemic. Or it might be, as Kawanishi suggests, "In the dimly
lit rain forests of Malaysia, black leopards are less visible than
spotted leopards—they are better concealed from prey and from the
tigers they share habitat with." In the end, the reason all Malaysian
leopards are black remains, like the cats themselves, a mystery.
Fiona Sunquist is a long-time contributor to National Wildlife.
National Wildlife Magazine Dec/Jan 2007