What Makes a Cat?

Cats have always been a part of my life. One of my earliest memories is of following our Siamese around to pet her (or him? I don't recall) and ending up wedged behind the fridge as a result. I lived without a cat after moving to Finland many years ago, but one found me while I was doing fieldwork, and I had to take her home. She still lives with me, nearly ten years later and on another continent, tolerating me as I tolerate her, her presence a welcome (or do I mean inescapable?) part of my mental landscape. As a biologist with a fondness for cats, I was excited to see a new paper in PNAS about the genetic changes that occurred during their domestication — just how did they manage to wheedle their way into our hearts so effectively?

An international team of researchers took on this question by comparing the genome of domestic cats with the genomes of tigers, dogs, cows, and humans. By using such a broad range, they were able to find sets of genes that underwent selection in groups of different sizes, from the domestic cat lineage to carnivores in general. Carnivores (including cats) need acute senses to be successful hunters, so it's not surprising that the team found signatures of selection acting on genes related to hearing and vision in carnivores. Smell, on the other hand, is one of the factors underlying a split within the carnivore lineage. Unlike dogs, felines — from tigers to house cats — don't rely on their sense of smell while hunting. This difference is clearly visible in the genomes, with a larger family of olfactory genes in dogs affording them a keener sense of smell. To me, one of the more striking things in the paper was the finding that lipid metabolism genes were a focus of selection in the ancestral cat lineage. Felines are obligate carnivores; dogs can eat a wide range of foods, but cats have to eat meat. As a consequence, they're unable to synthesize certain fatty acids, since they get them from their diet, but this also means that they can eat lots of saturated and polyunsaturated fats without increasing their risk of coronary heart disease -- unlike humans. It's a nice reminder that although we may live together, cats are, in many ways, starkly different animals from us.

So how did cats end up living with us, anyway? We know that cats started living with humans in the Middle East around 9500 years ago, thriving on the rodent populations that inevitably accompanied the development of agriculture. The friendliest cats and the friendliest humans got along, benefiting from each other in a comfortable companionship that continues to this day. Most of the human selection on cats probably happened early on; once they were (semi-)domesticated, we didn't breed them for tasks like hunting or plowing, or to use as food, unlike dogs, cows, horses, or many other domesticated mammals. Cat fanciers have bred 30 or 40 different breeds, but that selection is quite recent — in the last 150 years — and was based more on aesthetic considerations than utility.

To track down the changes that accompanied domestication, the team sequenced the genomes of 22 cat breeds and compared them with the genome of Near Eastern and European wild cats. They found 13 genes that had changed during domestication; several of which are known to play a role in cognitive and neural processes like fear response. Five of the genes also play a role in neural crest cell migration, lending support to the idea that changes in neural crest migration might underlie domestication syndrome, a suite of trait changes that seem to accompany selection for tameness when a species is domesticated.

It's endlessly exciting to be living in an era when biology is blossoming, when we're becoming able to use the genome as a lens through which we can look back across our interactions with other species — a sort of historical microscope for viewing how different creatures evolved, how we shaped them, and how they shaped us.

Ref
Montague et al. Comparative analysis of the domestic cat genome reveals genetic signatures underlying feline biology and domestication. PNAS Early Edition. (2014) doi: 10.1073/pnas.1410083111

Image credit
The photos are by Hannele Luhtasela-el Showk and are used with permission.