Scientific American - USA (2012-12)

December 2021, ScientificAmerican.com 25

G E N E T I C S

Tiger Fashionistas

A subpopulation of big cats with rare coloring

shows evolution in action

Tigers can indeed change their stripes—and in the Similipal Tiger

Reserve in India, many have done just that. So-called black tigers,

genetic mutants that sport unusually wide and merged stripes,

were extremely rare even when tigers were plentiful centuries

ago. But in Similipal today, one in three are black. A new study in

the Proceedings of the National Academy of Sciences USA pinpoints

the peculiar pattern’s genetic cause and reveals evolution at work

among these endangered cats.

After sequencing the genomes of three zoo-born black tigers

and their typical-coated parents, researchers at India’s National

Center for Biological Sciences and their colleagues tracked the

pattern to a tiny change in

a gene called taqpep. They

then spent months hiking

about 1,500 kilometers of jun-

gles across India, collecting

tiger droppings, fur, blood

and drool. Analyzing these

samples helped them deter-

mine the prevalence of this

genetic change—and its

virtual absence in tigers out-

side Similipal.

Altered taqpep genes were already known to cause blotched tab-

by patterns in cats, as well as king cheetahs’ unusually large spots and

stripes. But such patterns are so rare because they occur only when

genes from both parents have matching mutations. The new study

found that 10 out of the 12 Similipal tigers sampled had at least one

copy of this particular taqpep change—and four were black tigers,

with two copies each. But remarkably, not one of the 395 tigers sur-

veyed outside the reserve had even one copy of the mutation. This

suggests that the Similipal tigers are so isolated that they never

breed with tigers outside that range and that the group has begun

to maintain genetic changes over generations. “It was an astonishing

finding,” remarks molecular ecologist and lead author Vinay Sagar.

For senior author Uma Ramakrishnan, a molecular ecologist who

has studied Indian tigers’ diminishing genetic diversity for more than

a decade, this finding is “the most exciting discovery” of her career—

stark observable evidence of tigers’ fragmentation across the region.

The extensive data collected for this research “provide the much

needed baseline for further studies on the genetics of endangered

tigers,” says University of

Rochester evolutionary biol-

ogist Nancy Chen, who was

not involved in the study. Al-

though it is unknown if the

unusual stripes help or harm

the Similipal tigers, the mark-

ings underscore the fact that

these animals are breeding

exclusively among them-

selves—perhaps to their

own peril. — Spoorthy Raman

PANA M A

While monitoring vampire

bats in Panama, researchers

discovered that the blood­

thirsty fliers help one another

find food by screeching after

locating a juicy meal, despite

departing their roosts alone.

FRENCH POLYNESIA

Scientists reconstructed historic Polynesian

settlement routes by tracking rare gene variants

in DNA from hundreds of islanders. Findings suggest

that the shared tradition of carving massive statues,

such as the Moai at Rapa Nui (Easter Island), may have

originated at the Tuamotu Islands in French Polynesia.

For more details, visit

http://www.ScientificAmerican.com/dec2021/advances

SAUDI ARABIA

A massive collection of gnawed human and animal

bones found in the Umm Jirsan lava tube was

mostly left there by striped hyenas, researchers

report. Fossilized feces and other markers suggest

the site served as an underground den for the

animals from around 4,500 to 150 years ago.

BRAZIL

Three decades of Amazon satellite data reveal that illegal mining incursions

have quintupled on Indigenous lands in the past 10 years. These operations

contribute to the Amazon’s deforestation, which causes 8 percent of global

carbon emissions.

AUSTRALIA

Smoke from Australia’s 2019–

2020 bushfire season littered

the Southern Ocean with iron,

nourishing an unprecedented

algal bloom more expansive

than Australia itself. Al ­

though blooms consume

carbon dioxide from the air,

they can also suffocate or

poison marine life.

IN THE NEWS

Quick

Hits

By Nikk Ogasa

UZBEKISTAN

Paleontologists unearthed a 90­million­year­old dinosaur jaw­

bone belonging to new species called Ulugh beg saurus uzbek i­

stan ens is. The 1,000­kilogram dinosaur had serrated teeth and

was likely an apex predator, and its existence may have delayed

the rise of large tyrannosaurs.

Rajesh Kumar

Mohapatra Nandankanan Biological Park