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How wild is the Bengal cat genome?

People prize Bengal cats for their appearance; the exotically marbled and spotted coats of these domestic pets give them the look of small,

By Ground Report Desk 26 Mar 2024

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People prize Bengal cats for their appearance; the exotically marbled and spotted coats of these domestic pets give them the look of small, sleek jungle cats. However, the assumption that the origin of those coats comes from the genes of Asian leopard cats bred with house cats, turns out to be less unfamiliar.

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Researchers from Stanford Medicine, in collaboration with Bengal cat breeders, have discovered that domestic cat genes, aggressively selected for after breeding with wild cats, are responsible for the iridescent sheen and leopard-like patterns of Bengal cats.

In the 1960s, breeders created the hybrid breed of Bengal cats by crossing domestic cats (Felis catus) with Asian leopard cats (Prionailurus bengalensis), a small spotted wild cat species from Asia. The last common ancestor between these two species existed about 6 million years ago. The genetic differences between the two species exceed the differences between humans and chimpanzees.

In 1986, TICA officially recognized Bengals as a new breed, making them the only domestic cats that can display rosettes resembling the markings on leopards, jaguars, and ocelots. However, not all Bengal coats are equal. The initial hybridization of domestic and wild cats, followed by the selective breeding of Bengals for desired traits, introduced a variety of new coat colours and patterns.

Most people attribute the unique color and coat traits of Bengals to specific DNA from their wild and distantly related felid ancestor. Current Biology published a new study that delves into the fascinating genetics behind these captivating creatures. The study provides some genetic surprises and reveals the genetic secrets that create their unique appearance.

A community effort to demystify Bengal ancestry

“Most of the DNA changes that underlie the unique appearance of the Bengal cat breed have always been present in domestic cats,” said Gregory Barsh, MD, PhD, an emeritus professor of genetics. “It was really the power of breeding that brought them out.”

"Cats are wonderful companions," Barsh explained, "but our interests go beyond their beautiful and exotic appearance. Like the amazing variation among different dog breeds, artificial selection can be a very powerful engine to create morphologic diversity. What's different about Bengal cats from dogs is the raw genetic material–dogs trace their heritage to wolves from tens of thousands of years ago."

"In contrast, Bengal cats trace their heritage to completely different species from millions of years ago. Understanding how these distantly related genomes interact is a general question that applies to any situation when different species exchange genes, from crops to aquaculture to humans and Neandertals."

Barsh and his colleagues spent 15 years analyzing genes that they collected from nearly 1,000 Bengal cats. The paper lists Barsh as the senior author while the senior scientist, Christopher Kaelin PhD, assumes the role of the lead author.

Not only do the results shed light on the Bengal cat's coat, but they also answer broader questions about the encoding of appearance in genetics and the collaborative work of different genes to produce colors, patterns, and physical features.

“The big-picture question is how genetic variation leads to variation in appearance,” Barsh said. “This is a question that has all kinds of implications for different species, but we think that cats offer an especially tractable way to study it.”

Wild origins

In the period spanning the 1960s to the 1980s, biologist Jean Mills engaged breeders in cross-breeding the wild Asian leopard cat species known as Prionailurus bengalensis with domestic cats to bring forth a visually captivating new breed of cats. Over numerous generations, the breeders selectively bred and chose cats that exhibited the desired physical traits and behaviors. In 1986, the Bengal cat received recognition from the International Cat Association as a distinct, new breed.

Barsh and Kaelin viewed the Bengals as an exceptionally interesting approach to studying how genetic variation results in diversity in form, color, and pattern, due to their recent genetic origin and unique appearance. In 2008, they initiated contact with cat breeders, attended cat shows, and collected cheek swabs and photographs of Bengal cats.

"Cat fanciers and breeders show a great interest in our research, partly to understand more about the science behind artificial selection and partly to discover if our results can assist them in breeding cats with rosettes, stripes, or other exotic markings," said Chris Kaelin, the lead author of the study.

To enroll a cat in the Bengal research study, you need nothing more than a cheek swab for a DNA sample, photographs of both sides of the cat, and any records about pedigree or registration. The team has worked on the project for several years and collected nearly 3,000 DNA samples.

The work reveals one of the findings that Asian leopard DNA contributes, on average, only a few percent to Bengal breed DNA. Surprisingly, not one or even a few Asian leopard genes cause the unique Bengal appearance.

Kaelin said "their goal was to enhance the domestic cat with rare features of the wild Asian leopard. The most significant changes were already present but uncommon in domestic cats."

A boost for biology and breeders

The team describes in their paper that the "glitter" coat in Bengal cats exemplifies that phenomenon. The glitter doesn't involve any actual glitter particles, but instead, a unique structure of individual hairs that gives the fur a shiny and soft appearance. The team discovered a very popular trait in the Bengal breed caused by a mutation in a gene known as Fgfr2. "Fgfr2 is a gene found in all mammals and plays a significant role in embryonic development and organogenesis," McGowan stated.

"Our results show that while a complete loss of Fgfr2 is lethal, a moderate reduction causes a desirable trait to manifest mainly in the hair."

This study offers valuable results for cat lovers and for scientists who are generally interested in hybridization and selection. Barsh said, "Human DNA of European or Asian ancestry contains a small fraction of Neandertal DNA because humans caused the hybridization between the two species after they migrated out of Africa."

"In some ways, Bengal cats are similar, except the distance between the two hybridizing species is much greater and the time since hybridization is much less." From that perspective, learning more about Bengal cats could tell us more about ourselves.

The researchers say that we can learn lessons in just how powerful artificial selection can be, as probably, we could have selected the Bengal cat coats without the help of the Asian leopard cat.

“People have this idea that we have to get access to these distantly related animals to breed beautiful individuals and designer animals,” Barsh said. “But it turns out all the diversity was already there waiting in the domestic cat genome.”