Genetic Structure of the Cat Population

The earliest archeological evidence for cat associations with humans has been dated from 3000 to 6000 BC in Cyprus, Egypt, and China. Whether cats migrated to these different regions with trade and agriculture or if regional wildcats were independently domesticated in different parts of the Old World remains an unresolved mystery. Since these early times, cats have continued their friendship and symbiotic relationship with humans, providing vermin control while gaining low energy expenditure for meals.

As trade and exploration opened new opportunities and resources for humans, the cat expanded its territory around the world as our constant but often inconspicuous companion. However, similar to the formation of human ethnic groups and races, complete panmictic (random) worldwide breeding has not been possible for the cat, because it is limited by natural boundaries, few founders, and sporadic migrations. Thus, mutations and allele frequencies differ among cat populations, thereby forming races and breeds. Genetic studies of worldwide feral cat populations and breeds have shed light on the population structure of domestic cats, providing important clues to their genetic identity and genetic health management.

Genetic Races of Domestic Cats

The domestic cat likely derived from one or more subspecies of wildcat (Felis silvestris). At least one domestication event for the cat was very likely to have taken place in the Near East; however, independent domestications may be plausible due to the significant genetic distinction of cats in the Far East and the recent archeological find in China that associates cats with humans in an ancient agricultural site. Different domestication events from many, and perhaps different, subspecies of wildcats imply high genetic diversity for the founding population(s) of domestic cats. Such diversity should support health and the ability to adapt to different niches and physiological insults. Without archeological samples with sufficient DNA to analyze, only the present-day populations of cats can be examined to evaluate genetic diversity and population differentiations. These genetic data can allow the potential extrapolation back to the number and different sites of cat domestication. Regardless of the cat's ancient history, the present-day feline populations are the concern of owners, breeders and veterinarians.

Worldwide cat populations have been genetically examined to define the differences that may be important for genetic-based health management. Different genetic markers, such as mitochondrial DNA (mtDNA), short tandem repeats (STRs, or microsatellites), and single-nucleotide polymorphisms (SNPs), all have different "genetic clocks" and examine different time points in domestic cat history and evolution. The combined analysis of these different markers paints a picture of the present geographical demarcations and genetic distinction of cat populations. To date, several published studies have examined breeds, but only one has extensively examined feral cat populations. This study of feral cats has been expanded to include additional worldwide populations, refining the genetic races of feral cat populations. The DNA variants used for population studies are usually random DNA variants that are not important to health or physical appearance. However, one can infer that other genetic variants (such as those causing specific phenotypes, diseases, or health concerns) would have similar frequencies in the genetically similar populations.

Knowledge of the genetic similarities among cats in a particular geographic region can help prioritize differential diagnoses, particularly in the case of rare conditions. For example, gangliosidosis, a rare genetic condition documented in feral Japanese domestic shorthair cats, might be highly prioritized in sick cats from the region with compatible clinical signs of the disease. Cats from the United Kingdom share genetic composition with cats in the United States and Canada, and those in Australia, Kenya, and the Americas show similarities to their European counterparts. As such, veterinarians in Australia need to be cognizant of health concerns documented in cats in both the United States and Europe. However, founder effects and perhaps different selection pressures do make cat populations different that are historically similar. Feral cats in Turkey and Australia have different frequencies of blood type B, as compared to other regions of the world. Cats in Italy seem to be a conglomerate of individuals from the Mediterranean and other regions of the world. Despite these geographically distant relationships, cats in close proximity can have different genetic origins, such as those seen in the Iberian Peninsula and France. The Pyrenees mountain chain has apparently been an ecological barrier to cats; and like other species, cats of Portugal and Spain appear to be genetically different from the remaining European continental cats.

Overall, 11 different groupings, clusters or races of cats can be genetically defined from the various locations that have been sampled. Some island populations appear to have similar genetic signatures to the associated mainland (e.g., Majorca and Iberia), whereas others are more distinct (e.g., San Marcos Island off the coast of California). Distinct island populations are likely unique when cat migrations are very limited or forbidden, such as the case of San Marcos. In addition, this island is small and likely had a limited founding population. Thus, the lack of continued gene flow and limited founders have led to a genetically unique and likely highly inbred population of cats. For the development of cat breeds, in general, specific cats from a given race have been used as the founders of a given pedigreed breed.

Genetic Distinction of Domestic Cat Breeds

Genetically, breeds of cats are similar to ethnic groups of humans. Studies have shown that cat breeds were developed from western European, Mediterranean, Arabian, and Southeast Asian populations. Ongoing studies may suggest that breeds like the Norwegian Forest cat can now be refined to more specific populations, such as the northern European/Nordic race of cats. Thus, cat breeds share health concerns and genetic traits in common with their races of origin. The same types of genetic analyses that were used to compare feral, randomly bred populations of cats have also been used to compare different cat breeds. More than three dozen breeds have been genotyped with the same genetic markers as the cat races and compared genetically using allele frequencies of the markers. Approximately 24 breeds appear to be genetically distinct, whereas the remaining breeds are derived from a specific breed family, such as the Persian, the Siamese, or the Burmese families. These "parent" breeds have been bred to produce slightly different cat groups that are often declared a different breed, but are different by perhaps only one genetic variant. For example, the Persian family is composed of the Persian, Exotic Shorthair, Selkirk Rex, Scottish Fold, and British Shorthair breeds. Exotic Shorthairs are different from Persians by having short hair, Selkirk Rex differs by having curly hair, and Scottish Fold differ by having folded ears. Each difference is caused by a single gene mutation, which is not truly sufficient to affect the overall genetic constitution of the breed.

Cats of Madagascar

Madagascar is an island country in the Indian Ocean, off the coast of Southeast Africa. The island of Madagascar is the fourth largest island in the world, and split from the Indian peninsula approximately 88 million years ago. Because of its isolation from other continents, like Australia, the flora and fauna of Madagascar are unique and the island is biodiversity hotspot; over 90% of its wildlife is found nowhere else on Earth. The island's diverse ecosystems and unique wildlife are threatened by the encroachment of the rapidly growing human population and other environmental threats, such as domestic cats.

The human settlements of Madagascar are by Austronesian peoples that arrived approximately 350–550 BC. More recently, the French colonized Madagascar in the late 1890s, and the island is an important stop in the trade routes of the region. The cats that now invade the island are decimating the natural fauna; however, it is unknown if the cats are potential wildcats and perhaps a specific subspecies of wildcat or just feral domestic cats that came with the settling peoples. Cats from Southeast Asia are significantly different from those of the Arabian Sea region and cats of continent Europe, including France. We initiated a study using STRs mtDNA control region to examine the genetics of cat samples obtained from Madagascar via collaborators. We hope to identify with our studies if the cats of Madagascar are a unique population of cats that deserve a conservation plan versus feral cats that came to the island with historical or recent immigrants. The genetic race of the cats will help determine where the cats have come from and their historical geographic origins.

Acknowledgements

Feline Genetics Laboratory at MU

Barbara Gandolfi, Erica Creighton, Nick Gustafson, Madison Bullock, Victoria Spreyer, Sara Shippey, Destiny Monroe, Jena Grahn and Ashley Bullock.

Madagascar Research Collaborators

Michele Linda Sauther, Julie Pomerantz, Julie Feinstein, Luke Dollar, Scott Larsen, Frank Cuozzo