Why Are Black Leopards So Rare?
Several species of cat have members with all-black coats, but the evolutionary advantages and disadvantages are just starting to be understood
Black leopards are mysterious cats. With a rare variation of the generally spotted carnivore’s coat, they blend into the shadows and are nearly invisible in the dark. But the black fur that provides a boost to sneakiness could come with a cost to communication—and new research may explain why wild, all-black cats are relatively rare.
The black color variants of cats like leopards, jaguars and ocelots are known by experts as “melanism.” Over the years, researchers have come up with a handful of hypotheses to explain why some wild cat species have these darker coats. The black cats are likely better concealed at night, but the variant may also allow cats to warm faster in the sun or even ward off certain parasites. But the trouble with being an all-black cat, a new study in PLOS ONE suggests, is that markings critical to feline communication get obscured.
Melanistic cats are not as black as a moonless night. Often, their spots are still visible. But black leopards, jaguars and other wild cats lack the white markings on their ears and tails that other members of their species often use to signal to each other. This inability to communicate with other cats, zoologist Maurício Graipel of the Federal University of Santa Catarina in Brazil and colleagues argue, raises difficult challenges for the black cats.
Even though the study has implications for larger, famous felids, the inspiration for the research came from a smaller cat. While studying the habits of the southern tigrina in Brazil—a wild species similar in size to a housecat—the research team noticed that the black individuals lacked the white spots seen on the others. “Since white is the most light-reflecting color,” Graipel says, “we considered that these white marks might play a role in visual communication during the night.”
The zoologists considered 40 cat species, 15 of which have black coat variants. They also considered whether the cats were active primarily during the day, night or both, as well as whether they had conspicuous white marks to flash signals to members of the same species.
Surprisingly, the black cats didn’t prefer the cover of night any more than the other cats. “There was no difference between day and night activity of melanistic and spotted individuals,” Graipel says. The black coat color acts as camouflage at almost any time, but therein lies the problem. When a black cat runs into a spotted cat, it may not be easy for them to understand each other.
Cats use various cues to communicate with each other, from pungent scents to a variety of chirps and growls. But visual communication plays a significant role, too. The white markings on the ears and tails of spotted cats can carry a variety of messages, from friendly intent to “back off!”
One example is that mother cats can lift their heads and stretch their ears to flash the white marks to signal possible danger to their cubs, or to keep quiet if prey is nearby. “It is as if you step on the brake of your car to warn those behind you that there is danger ahead,” Graipel says.
But consider a melanistic mother cat with spotted kittens. She could read the kittens signals, but they might not be able to see or understand their mother’s. As a result, they may be loud when they need to be quiet, or they may stumble into danger. The same may be true for adult cats. A black cat can understand the intentions of a spotted cat, but, in low light, a spotted cat may have difficulty communicating with the melanistic cat. This inability to effectively communicate could account for the relative rarity of most black wild cats, the study hypothesizes. They simply can’t talk to their spotted neighbors and therefore have more difficulty courting mates and raising offspring.
“I think the paper presents an intriguing set of hypotheses and valuable data, but I also think that many of the inferences are indirect,” says Greg Barsh of the HudsonAlpha Institute for Biotechnology. Wild cats are rare and elusive, he notes, which makes it difficult to directly test hypotheses like the one proposed by Graipel and co-authors.
In previous work that Barsh carried out with one of the authors of the new study, he says, a small feline called the pampas cat showed signs of evolutionary selection for black coat color, but two others did not. “In some cases, a likely explanation for the different frequencies of melanism observed among some felid species is genetic drift,” Barsh says, or a particular mutation gaining prominence through chance. Additional fieldwork and experimental studies are needed to parse what might be going on in any cat species. Still, Barsh says, “I think the strongest and most interesting observation is that species in which melanism is found also tend to be species that have white marks on their ears,” hinting that these species heavily rely on visual cues.
An exception to the hypothesis laid out in the new study be the best evidence for a tradeoff between camouflage and communication. A small cat called the jaguarundi has the highest proportion of melanistic individuals of any species. About eighty percent of jaguarundis are black. But these cats, the researchers note, are mostly active during the day. Interacting in well-lit ours seems to jump the communication barrier than other melanistic cats, that are more active at darker times, have to cope with.
One advantageous or limiting trait is not all that affects cat coat color. Camouflage and communication can sometimes be in competition, which raises a speculative evolutionary question. “If the presence of white markings behind the ears is so important for silent visual communication for felines,” Graipel says, “what would felines be like if a mutation had not originated the white markings?” How the leopard got its spots is not just a fable, but one a prevailing evolutionary mystery.