Covering the coverage of the fox genome paper

Ah, the beloved Tame Fox Project! I worked in a lab that focused on these foxes for four years, during my PhD in Kukekova Lab at the University of Illinois at Urbana-Champaign. We worked on analyzing the fox genome for publication throughout those four years, and now at last the fox genome paper is published. (You can see my name tucked neatly in the middle of the authors list.)

What does it mean to have the fox genome sequenced and published? There is a flurry of news reporting about it, and I have issues with a lot of that coverage. I'll be covering the coverage here, letting you know what is accurate and what is less so. I'll update this post as I cover more articles.

Feel free to comment with questions, or with news stories you think should be included here.

• Fox ‘tameness gene’ identified in 60-year study (Independent): the title of this story is irresponsible, implying that there is one gene controlling tameness in these foxes and that that gene was discovered. The story itself does a decent job of untangling the facts: that a large number of genes affect tameness, and that the gene that was discovered influences whether the fox wants to continue to interact with humans during a specific behavioral test. However, I wonder how many people just read the headline and took away a very different message.
• A Soviet-era experiment to tame foxes may help reveal genes behind social behavior (Washington Post, Animalia): Great title, intriguing and also accurate. However, the story itself over-emphasizes the morphological difference in the foxes, stating that the Tame Fox Project "spawned an ongoing area of research into how domestication, based purely on behavioral traits, can result in other changes — like curlier tails and changes to fur color." We still don't know if the morphological changes in the tame foxes (which are much less frequent than most journalists suggest) are related to their behavioral changes, or if they're just a result of founder effect. (The lab that produced the current study is betting on founder effect.) The rest of this article is good, with an excellent description of the study's design.
• Sequenced fox genome hints at genetic basis of behavior (ScienceDaily): "today, with the first-ever publication of the fox genome, scientists will begin to understand the genetic basis of tame and aggressive behaviors" - I think this is overstating. The fox genome is an important tool for working with the genetics of tame foxes, and they are an important model for understanding the genetics of tame behavior. But this isn't the beginning of understanding the genetic basis of tame behavior - either we started that a long time ago, or we haven't really started yet, depending on how you look at it. As with other stories, this story also calls out the finding that there were some changes in aggressive foxes in a region similar to the one associated with Williams syndrome (hyperfriendliness, among other traits) in humans. Which is cool - but don't forget they also found changes in regions associated with autism and schizophrenia, which is also cool! (And which gives more perspective to the fact that a lot of changes were found in a lot of regions, and we don't know what any of them mean yet.) This story has a nice description of the behavioral trait associated with the SorCS1 gene, the one gene that the paper focused on that has changes associated with behavioral differences in tame foxes.
• The first detailed map of red foxes’ DNA may reveal domestication secrets (ScienceNews): wow, I really like this one! Read this one! It does a great job summarizing the paper, it pulls out interesting stuff, and it doesn't ever go overboard in its interpretations.
• Friendly Foxes’ Genes Offer Hints to How Dogs Became Domesticated (New York Times): quite short, so other articles are better bets for you to learn more about the study. However, I want to give a shout-out to this one for 1) not saying anything misleading and 2) explaining that tame foxes aren't great pets - something that can be really valuable to include in stories like this one.

Corrigendum on a recent tame fox article

I came across a new article on the Russian tame foxes today, Russian geneticist repeats dog domestication with foxes in just fifty years. It's a nice summary of the Farm Fox Experiment, although I’m not sure why I've seen two stories covering the tame foxes this week — there’s nothing new going on with them! Why two stories in such a short time period?
 

This article does have a few mistakes in it:

 

[Belyaev] and his intern, Lyudmila Trut, wandered around Russia searching for foxes to start their experiment. Foxes were chosen based on their behavior in the presence of humans. Those that showed slightly more tolerance of humans were brought back to their Novosibirsk lab to serve as the start group.

and his intern, Lyudmila Trut, wandered around Russia searching for foxes to start their experiment. Foxes were chosen based on their behavior in the presence of humans. Those that showed slightly more tolerance of humans were brought back to their Novosibirsk lab to serve as the start group.

Read more at: http://phys.org/news/2016-09-russian-geneticist-dog-domestication-foxes.html#jCp

and his intern, Lyudmila Trut, wandered around Russia searching for foxes to start their experiment. Foxes were chosen based on their behavior in the presence of humans. Those that showed slightly more tolerance of humans were brought back to their Novosibirsk lab to serve as the start group.

Read more at: http://phys.org/news/2016-09-russian-geneticist-dog-domestication-foxes.html#j

and his intern, Lyudmila Trut, wandered around Russia searching for foxes to start their experiment. Foxes were chosen based on their behavior in the presence of humans. Those that showed slightly more tolerance of humans were brought back to their Novosibirsk lab to serve as the start group.

Read more at: http://phys.org/news/2016-09-russian-geneticist-dog-domestication-foxes.html#jCp

 

 The original foxes were imported from Canadian fox farms, not chosen from around Russia as this article says. Also, the very first foxes selected for the founding population of the study were not chosen based on their behavior. A control group was kept, so the researchers (of which there are more than two) didn’t want that first set to be more friendly than the average farm fox.

 

[The changes were] not all on the outside—their adrenal glands became more active, resulting in higher levels of serotonin in their brains, which is known to mute aggressive behavior.

 

The tame foxes’ adrenal glands became less active, and secreted less cortisol, a hormone which is associated with stress. Additionally, they have been shown to have higher levels of serotonin in their brains (not secreted by their adrenals, however), which is associated with less aggressive behavior, though I think saying that serotonin “mutes” aggressive behavior might be going a bit far. We don’t fully understand the link between serotonin and aggression.

I do like seeing the Farm Fox Experiment covered in the popular press, though. It’s such a great way of explaining how selection works and such a fascinating demonstration of how quickly selection can have an effect!

And it was not all on the outside—their adrenal glands became more active, resulting in higher levels of serotonin in their brains, which is known to mute aggressive behavior.

Read more at: http://phys.org/news/2016-09-russian-geneticist-dog-domestication-foxes.html#jCpMore importantly, the adrenals don’t control serotonin levels in the brain. They release cortisol into the blood stream. Tame foxes show reduced levels of both cortisol and serotonin compared to control foxes, but those are two different things.

 

Ruminations of a dog scientist on a 96-well plate

I've been doing a lot of bench work in the laboratory lately. This involves filling the tiny little wells on a plate with my ingredients (sample, reagents, primers) and then inserting the plate into a reader. The machine takes the plate up with whirring sounds that always fascinate me. I know there are little robot arms in there moving the plate into place, and I wish I could watch the process. But as I listen to the robot work, I sometimes think: is this the closest I get to living, moving animals now? How did I get here, so separated from fur and behaviors and emotions?

96 well PCR plate

My long term research goal is to understand the differences in how brains work in dogs who suffer from fear issues compared to resilient dogs who take life's arrows a bit more in stride. I'm doing this by studying gene expression in the brains of foxes who have been bred to be fearless (“tame”) or fearful (and aggressive — those who study them just refer to this line as “aggressive,” though).

My approach is, at the moment at least, deeply reductionist: what are the differences in gene expression in a few brain regions in these two lines of foxes? In other words, does one group make more of a certain kind of gene than the other? My hope is that I’ll be able to make some conclusions about the differences in function in these brain regions between the two lines of foxes, and that what I find will be relevant to fearful dogs. But I find myself burrowing deeper and deeper into learning about very small parts of the brain, and then very specific functions of those parts to the exclusion of other parts. Currently I’m learning about the pituitary gland — no, wait, just a particular cell type in the pituitary gland, the corticotroph — no, wait, just a particular set of processes of the corticotroph, how it releases one particular hormone into the bloodstream.

So in my daily work, I do things like take some tissue and extract all the RNA from it (throwing out DNA, proteins, cell structure, all sorts of interesting information — that's not what I'm working on or able to assess at the moment). I use PCR to extract a tiny piece of RNA from the complete transcriptome (all the RNA from that tissue), throwing out even more information. And then assess the expression level of that RNA, resulting in just one number. One number out of all that information after a day’s work.

Behavior can’t really be fully understood using this reductionist approach. If I do find a few important gene expression differences in a few small brain regions, they won’t explain the whole story of why an animal has a fearful personality. They’ll be a tiny, tiny piece of a complicated network of interactions involving genetics and life experience. But in order to get at that tapestry we have to first be able to visualize the threads that make it up. So here I am, in the trenches, doing that.

A recovering shy dog.

A week of tame foxes

“You're checked all the way through to... some place I can't pronounce,” said the woman who was checking me in at my small local airport in Illinois.

Novosibirsk. It is the third largest city in Russia, located in south-western Siberia. It is the location of the Novosibirsk State University, one of the best universities in Russia, where the Institute of Cytology and Genetics maintains Belyaev’s tame foxes.

(You may already know about the fox domestication project, but if you don’t, Wikipedia has a good primer, and Jason Goldman has written about them.)

The Institute is actually in Academic City (Akademgorodok), a suburb of Novosibirsk. Academic City is an odd blend of the European — my hotel would not have been out of place in France — and the Russian, with its thick stands of birch and fir. During my early April visit, there was still three or four feet of packed snow on the ground, and mud season was commencing as the temperature rose.

The Institute is in a green-roofed building shoulder-by-shoulder with other university institutes. The farm, where the foxes live, is a ten or fifteen minute drive out of the city. I went to the farm daily to study the socialization period in tame and aggressive fox kits.

Tame fox kit (silver color)

I was working with these kits at three weeks of age, before they were old enough to start venturing out of the nest and interacting with the world. At this point they shouldn’t yet have entered their socialization period. Yet you could already tell the difference between the tame kits and the aggressive kits. Kits within a group weren’t identical in behavior: some complained about being restrained, some yelled, some fell asleep, some were calm and silent. However, the aggressive foxes tended to make more noise, and the tame foxes tended to be more curious about their surroundings. Two aggressive fox kits tried to bite. One tame kit did.

As for the adults, I found more behavioral variation than I’d expected there as well, although the head of the laboratory where I work had warned me again and again that the foxes vary sigificantly in behavior. Tame foxes were curious and wanted to interact with us, but some were shy, diving into their nest boxes or to the far side of their cage and then returning slowly. One fox stretched his body out, low to the ground, so that he could sniff my companion’s face without having to commit himself to coming too close. (When I offered to let him sniff my face, he stole my hat and then carried it around his cage while the neighboring foxes watched in fascination.)

Slightly shy tame fox (Georgian white color)

Other tame foxes could not contain their enthusiasm at having people to interact with. They rolled on their backs and made excited yipping noises and wagged their tails. In their joy, they would hold our hands gently in their mouths, something I saw again and again with them but that I have very rarely seen a dog do.

Fox holding my hand in his mouth (platinum color)

I visited foxes from the control line, who had not been bred for behavior. They were simply afraid of us: when their cage door was opened, they retreated. If cornered, they would bite, but any aggression they showed was entirely defensive.

I also saw foxes from the line that has been selected for aggression to humans. Some of them were afraid and aggressed only defensively. Some were more scary, coming forward to the front of the cage to bite again and again. Certainly they were afraid of humans, but something in their brains or hormones makes them more proactive and less passive in their defensive aggression.

Finally, I met rats and mink selected for tameness or aggression. The tame rat that I met was happy to be held and happy to interact with me, but I don’t have enough experience with pet rats to say if this was unusual. The aggressive rat that I met was terrifying, hurling herself at a gloved hand when her cage door was opened and screaming repeatedly, even after we backed off.

The tame mink were less curious than the tame foxes and didn’t seek interaction with humans in the same way. One let himself be held by his keeper but I wasn't allowed to touch him, in case he might try to bite.

Tame mink

Notice the little white patch on his chin — more white coloration is associated with more tameness in both minks and foxes. Another, all-white mink was tamer and I could pet him. He seemed deeply passive, not seeking interaction, just tolerating it.

Tame white mink

Remember that part of the tame fox story — that as the foxes were selected for tame behavior, they started showing characteristics typical of domesticated species, including white patches and curled tails? Only a small percentage of the tame animals have these features, but I saw several piebald fox kits:

Piebald fox kit (silver color)

...and my host kindly pointed out one fox with a gorgeous example of a curled tail.

Fox with curled tail

What an amazing week. I kept thinking: how strangely my life has turned out!

The star coat pattern in foxes: what does it have to do with tameness?

Despite my previous voracious reading about tame foxes, as I settle in to my new lab I’m realizing how much I don’t know about them. For example, one of the most interesting things about the tame foxes is that although they were selected just for behavior (not running away from a human approach), they have physical changes as well, and those changes mimic physical changes between wolves and dogs: the appearance of white patches of coat color, floppy ears, and curly tails. I have learned that this is not an example of white patches related to tameness:

Platinum fox

That is a platinum fox, a color morph unrelated to the white coat markings that seemed to appear with tameness. The white coat markings come from the star gene. So what do we know about the star gene? What do those markings look like?

I started my hunt for information about the star gene in my own reference manager, since I knew I had read about it before. The only paper I had saved about it was from 1981 (!) but it was written by the mastermind of the farm fox project, Dmitri Belyaev, so it seemed like a good enough place to start.

Belyaev D.K. (1981). Inherited activation-inactivation of the star gene in foxes: Its bearing on the problem of domestication., Journal of Heredity, 74 (4) 267-274. URL: http://jhered.oxfordjournals.org/content/72/4/267.short

So back in 1981, when rock music was just starting to get really good, Belyaev was pondering the trickiness of the star gene. At that point, the tame fox project was only 20 years old. In 1969, the first white-spotted fox was born on the tame fox farm, with spots on his head and paws. Other foxes followed. The images from the paper show them looking like this (apologies for the poor image quality — it’s all I have to work with):

Fox kits heterozygous for star allele

This star pattern was not completely new. It had appeared on other fox farms, in foxes that were not selected for tameness. However, it was appearing much more often in foxes on this farm that were selected for tameness. In fact, the three families of foxes that were the most friendly to humans were showing this color pattern the most often. Unselected (not tame) foxes showed this star pattern 1.1% of the time, on multiple farms. (This includes foxes on the experimental farm which were from lines that were not selected for tameness.) Foxes in tame lines showed the pattern 3.7% of the time, or more than three times as often.

By the way, the fox kits shown above have only one copy of the star allele. Animals with both copies of this allele look much more like border collies:

But you can see how the non-white parts of their coats are a dark silver, unlike the platinum fox pictured at the top of this post.

Anyways, the question was: why were the tame foxes showing this pattern more often than conventional foxes? The pattern is particularly intriguing because it looks so much like the patterns we see in coats in domestic dogs, as well as in domestic horses and other domesticated animals. Was it possible that whatever mechanism was making these foxes more friendly to humans was also affecting their coat? The other explanation is just as likely but a lot less interesting: that when foxes were selected for tameness, the ones that were chosen just happened to have more copies of the star allele in their gene pool than average. Inbreeding would then cause this allele to show up more often.

Belyaev looked at family trees of foxes showing this pattern, trying to figure out if the gene for star pattern was recessive or dominant. The genealogy he found was somewhat perplexing. It didn’t follow the structure you'd expect for either a dominant or a recessive trait. The trait appeared to have variable penetrance, meaning that some animals with the star allele showed the star coat pattern, but some didn’t have star patterns, despite having the allele for it. This, of course, begs the question: if you have a group of animals, all of whom have the star allele, why do only some of them actually have the star coat pattern?

There are some possibilities:

• There may be a hormonal difference in the tame foxes which changes the effect of the star allele. In other words, the hormonal soup of a tame fox (less cortisol, less adrenaline) may affect coat color during development, so that those foxes are more likely to express the star allele if they have it. Conversely, the hormonal soup of a conventional fox (more cortisol, more adrenaline) may somehow suppress expression of the white spotting.
• The star allele has been around for a while, but perhaps it appeared in lower numbers in conventional foxes because it was somehow inactivated. Something about breeding for tameness may have activated the gene so that it was not “turned off” as often in tame foxes.

In 1981, no one knew which of these stories was more likely. This was before epigenetics was a hot topic, for one thing. But the nice part about reading historical papers like this one is that sometimes the answers to their questions exist in more recent literature. Which I am going to go hunt down now.

Fox colors

Tame fox kits

We often talk about the tame foxes as “silver foxes,” but in fact there are multiple color morphs in the tame population, not just silver. All of the foxes you’ll see here are the same species, Vulpes vulpes. The silver color morph was the color used for the first foxes which were selected for the creation of the tame population, but other morphs were brought in later.

Here is the silver morph, the color we are all most familiar with as being the color of a tame fox:

Tame silver foxes

My personal favorite fox color is Georgian white. The picture below is the one on my phone background.

Tame Georgian white fox

The ones that look so much like they have border collie markings, which are that lovely lighter silver color, are counterintuitively not called silver; they’re called platinum:

Tame platinum fox

And, of course, there’s the traditional red color, which somehow always surprises me the most to see on a tame animal:

Tame red fox

A rainbow of foxes!

Repost: Learning from Domesticated Foxes

[This was originally a guest post on The Thoughtful Animal.]

Everyone loves reading about the Siberian fox experiment because domesticated silver foxes are so damn cute. There’s something deeply appealing about the idea of a cuddly fox. And the experiment raised some interesting questions about domestication. Could domestication really happen in just eight generations? (Apparently.) Domestication must just affect the brain and not the rest of the body, right? (Apparently not – domesticated foxes can have characteristic coat color changes, floppy ears, and curly tails, similar to morphologic differences between dogs and wolves.) But a research population of domesticated foxes hasn’t been maintained since the sixties just because they are cute. We’re still learning things from them. Like what? Get ready for some well-aged papers; a lot of this work was done back in the eighties.

Hormone and neurotransmitter soup

We use the hormone cortisol as a marker of stress: if you have more cortisol in your blood, you’re probably more stressed. It turns out, perhaps not surprisingly, that domesticated foxes have lower basal levels of cortisol than their unselected counterparts (Oskina, 1992). Their cortisol levels also don’t go up as high during a stressful experience as do the cortisol levels of unselected foxes (Harri, 2003). Personally, I think cortisol is going to play a key role in the mechanism of why domesticated animals are less flighty than wild ones. Cortisol levels influence the production of adrenaline: if you have more cortisol in your system, you are liable to make more adrenaline (Kvetnansky, 2009). If you have more adrenaline in your system, you are going to react more strongly to scary stimuli – in other words, your flight distance is going to increase. (Quick review – domesticated foxes were bred by selection for decreased flight distance from humans.) My friends and I noticed during our highly stressful first year of veterinary school, when our cortisol levels were certainly high, that were were inexplicably jumpy. One friend reported that she was so startled by the noise of a dropped glass that she actually screamed.

As for the ever-popular serotonin, the “happy hormone,” domesticated foxes have more of it in their midbrains and hypothalamuses (Popova, 1991). Yes, the same hypothalamus that is the beginning of the hypothalamic-pituitary-adrenal axis, which ends in the release of cortisol. Oh, and which is inhibited by having more cortisol already in the system, in a negative feedback loop.

There is nothing cuter than a baby domesticated fox

Wolf cubs have a much shorter socialization window than dog puppies, and this might be part of why it is so difficult to socialize a wolf cub to humans. It turns out that unselected fox kits have a shorter socialization window than domesticated fox kits, too. Prime socialization time in both lines seems to start around 30-35 days, when the kits can see and hear and are mobile enough to explore their surroundings. Like most very young animals, fox kits of this age aren’t as fearful as their adult counterparts; they have a chance to learn what is dangerous and what is not in their particular environment. A longer socialization window gives you more chances to learn that a variety of beings are not dangerous to you, but in the wild it also gives you a greater chance of getting eaten by something that is dangerous to you when you wander up to say hello to it.

Domesticated fox kits start showing fear of new objects after age 60-65 days. Unselected kits, on the other hand, start fearing novel things at day 40-45 (Belyaev, 1985). We don’t know what exactly causes this difference in a preprogrammed socialization window, but it’s very helpful to have these populations as we look for the cause.

An even lower level of programming

In recent years, researchers have had new tools to use in exploring the mechanisms of domestication in foxes, especially since the canine genome was sequenced. Comparing gene expression in the wolf and the dog is problematic, because they necessarily live in such different environments. Comparing gene expression in two populations of foxes raised in identical conditions is potentially much more fruitful. This research is in the early days. But as we learn more about the canine genome I think we’ll start finding some really interesting differences between the lines of domesticated and unselected foxes. My personal belief is that we’ll find subtle differences – maybe, rather than differences in actual genes, we’ll see changes in promoter sequences, which cause significant genes to be up or down regulated.

We’ve learned a lot from the Russian domesticated foxes so far, but we have a long way yet to go. We still have no real idea exactly what is at the root of the difference between a domesticated and undomesticated animal. Does the change in development affect cortisol and serotonin levels, or vice versa? Does just a single genetic modification cause all the physiologic changes we see? Or are we looking for a set of modifications? Hopefully the new genomic tools we’re developing will allow us to get to the bottom of the mystery.

References

OSKINA, I., & TINNIKOV, A. (1992). Interaction between cortisol and cortisol-binding protein in silver foxes (Vulpes fulvus) Comparative Biochemistry and Physiology Part A: Physiology, 101 (4), 665-668 DOI: 10.1016/0300-9629(92)90341-M

Harri M., Mononen J., Ahola L., Plyusnina I., Rekila T. Behavioural and physiological differences between silver foxes selected and not selected for domestic behaviour. Animal Welfare. 2003:305-314.

Kvetnansky, R., Sabban, E., & Palkovits, M. (2009). Catecholaminergic Systems in Stress: Structural and Molecular Genetic Approaches Physiological Reviews, 89 (2), 535-606 DOI: 10.1152/physrev.00042.2006

POPOVA, N., VOITENKO, N., KULIKOV, A., & AVGUSTINOVICH, D. (1991). Evidence for the involvement of central serotonin in mechanism of domestication of silver foxes Pharmacology Biochemistry and Behavior, 40 (4), 751-756 DOI: 10.1016/0091-3057(91)90080-L

BELYAEV, D., PLYUSNINA, I., & TRUT, L. (1985). Domestication in the silver fox (Vulpes fulvus Desm): Changes in physiological boundaries of the sensitive period of primary socialization Applied Animal Behaviour Science, 13 (4), 359-370 DOI: 10.1016/0168-1591(85)90015-2

Domesticating foxes for fun and profit

The Thoughtful Animal has been writing about domesticated foxes and has pointed out that they are commercially available.

Dude! I want one right now! For the low price of $5,950, why not?

Let’s assume the cost isn’t actually an issue. (I want one of these guys badly enough that I would probably find the money somewhere.)

It’s just like a dog, and we know all about taking care of them. It won’t be like owning an exotic animal. It will be like owning an extra cute dog.

Well, it isn’t exactly just like a dog; they aren’t closely related enough to interbreed, for example. One thing vet school has impressed upon me is that species differences jump out at you when you least expect them. We have lived with dogs for a long, long time. In fact, I will hazard a guess that veterinary medicine was practiced on them very early. We know a lot about what makes them tick. We don’t know all that much about foxes.

Well, I live just up the street from a wildlife clinic. They could provide veterinary care.

Actually, in my case, this is true. However, the approach to veterinary care at a wildlife clinic is different from the approach at a small animal veterinary clinic. Ask me again after I have done my wildlife rotation, but I imagine they are not as used in that clinic to the kind of care we expect to give to our pets. For example, I had cardiology specialists caring for my cat when she was in heart failure. They knew all about how cats respond to heart failure (differently from dogs). Cardiologists wouldn’t have the first idea about species differences in foxes, but the wildlife clinicians would be much less skilled at reading a cardiac echo. Neither would be quite able to provide complete care for a pet fox. And the number of foxes a wildlife veterinarian sees a year is much, much smaller than the number of dogs a small animal veterinarian sees a year. It would just not be the same as getting veterinary care for a dog.

My guess is that your local vet would refuse to see the fox at all, with good reason. If you know someone who owns a bird or bunny, ask them how hard it is to find a vet to see one of those animals! And if you can only find one vet who’s even willing, you will have no choice of where you get care.

This will be a young, healthy animal, so I’m not worried about veterinary care.

Are you worried about behavior?

It’s domesticated. That means it’s just like a dog.

In this case, the foxes were “domesticated” by being bred to not be afraid of humans. They weren’t bred to be good house pets, though. They have been maintained as laboratory animals since their strain was developed, living in runs. They won’t bite you. But they may chew up your house, kill your cat, pee inappropriately — actually, a dog will do any of those things. Who knows what else a fox might come up with? We don’t have all the experience with their quirks that we have with dogs.

I’ll take him to a good trainer and make sure none of those things happen.

I’m betting you will have trouble finding a dog obedience class which will allow him in. You will have to shell out for private lessons.

Well, I’ll get him lots of exercise. A tired fox is a good fox.

Who will play with him? Will you take him to the dog park? Will his unusual smell and unusual body language (I’m just guessing here that a different species speaks a slightly different language) make it harder for dogs to accept him? Is it OK with you that he will never see another member of his species for the rest of his life?

And what will you feed him?

Dog food, of course.

There’s a lot of debate over what’s healthy food even for a dog these days. Again, we don’t know as much about foxes. And remember, they are only maintained in the laboratory for a few years, so the researchers don’t have experience with what is healthy for them as they get old. How hard is it to feed an animal right? Well, before we discovered that taurine was a required nutrient for cats, cats which ate commercial cat food tended to go blind as they got older. What might we be missing in a fox’s diet?

We take a lot of things for granted with dogs, and even so, they can be a big commitment. I really, really want a domesticated silver fox. But it is not a good idea for me or anyone else to have one. We have plenty of species of domesticated animals already which make excellent pets about which we know a great deal. We have a much better chance of providing good husbandry for a dog or cat. The foxes make for fascinating research animals, and I am glad that they exist (though I am sad that they have to live in a laboratory in order to be studied). But turning them into pets is not a responsible thing to do.

Rats, dogs, foxes, and the SHRP

Working on my Master’s degree has made me yen for more letters after my name, so I’ve been doing some spare-time reading on subjects that might yield PhD-type projects. My putative interest is in development of the stress system in young dogs. The idea is that if a dog’s stress system develops poorly, whether through bad genetics or a bad early environment, then that dog is more likely to bite people when it grows up. The more we know about how their stress system develops, the more we can know about how to grow healthy dogs with good bite inhibition.

For several months I thrashed around in the literature, reading about development of the stress system in rodents (about whom we know quite a bit, because we are more willing to do experiments on them than on dogs), and reading about socialization periods in dogs. It was hard to find good direction, and I wasn’t quite sure where to start. Recently I have had a breakthrough, however.

First, some orientation. You are walking through the woods. You see a shape on the ground. Your brain interprets the shape: long, thin. Your amygdala (part of the limbic system of your brain) yells SCARY SHAPE SCARY SHAPE and you get a blast of adrenaline in your system. Half a second later your cortex (the thinking, conscious part of your brain) catches up: hey, that looks like a snake. Your hypothalamus (which deals with a lot of hormone regulation) sends a message to your pituitary (which releases a lot of your hormones), and the pituitary releases a hormone which travels down to your adrenals, near your kidneys. Your adrenals release our old friend cortisol, which gets into your blood and tells your body that you are having a stressful experience. Cortisol, you of course remember, is what I like to extract from the saliva of dogs to tell if they are unhappy about being stuck in a noisy hospital run. This whole system is what I’ve been referring to as the “stress system,” more properly called the HPA (hypothalamic-pituitary-adrenal) axis.

If you were a rat or mouse, instead of releasing cortisol, your adrenals would release corticosterone. It is a very similar hormone with similar effects. Dogs actually release equal parts cortisol and corticosterone, but we just study their cortisol levels. I still haven’t figured out why we chose cortisol to focus on in them; there are a lot of tools available for studying cortisol, since humans make it primarily, but also a lot for studying corticosterone, since we study rodents quite a bit.

Now, to get back to my recent reading, very young animals don’t get as frightened by scary things as slightly more mature animals or adults. This phenomenon has been studied intensively in the rat: rats younger than two weeks of age don’t show this corticosterone spike when exposed to something upsetting. This is called the “stress hyporesponsive period,” or SHRP.[1] There has been work on what part of the HPA system is responsible for this blunted response: the amygdala? The hypothalamus? The pituitary? Or are the adrenals themselves not responsive yet?

A good way to stress out an infant rat is to expose it to the odor of an adult male rat. Left to their own devices, adult males will happily eat infants, so the young rats are quite right to fear them. An infant rat, upon smelling a strange adult male, will become immobile. However, a neonatal rat younger than 14 days (in other words, one still in the SHRP) will not become immobile: it hasn’t yet developed the machinery to feel, or possibly just to express, fear. If you remove the infant’s adrenals, so that it is unable to make corticosterone, then even when it matures to older than 14 days it will still not properly become immobile when exposed to the scary smell. Moreover, if you inject corticosterone into one of these pre-14 day rats, it will be able to develop the immobility behavior at age 14 days, just like a normal rat. [2] This suggests that corticosterone is responsible for the immobility behavior. However, if you remove the adrenals of a rat which has already developed the immobility behavior (one which is older than 14 days), it will continue to become immobile in the presence of the scary smell. [3] And if you inject extra corticosterone into a rat too young to have developed the immobility behavior, it will develop it early. [4] This suggests that corticosterone is responsible just for the development of the behavior, not for allowing it to actually happen at specific times once it has initially appeared.

What’s going on up in the brain while all this is happening? When infant rats are too young to express (or possibly feel) fear, are their amygdalas just failing to activate? When neurons in a particular brain region have been recently active, they contain a protein called c-fos. You can check a brain region for the prescence of extra c-fos to see if it has been doing anything in the recent past. This was done with young rats. Rats too young to have developed the fear response did not have amygdala activity (no extra amygdala c-fos) after exposure to the scary smell; if they were injected with corticosterone to cause them to develop the fear response early, then they did have amygdala activity; rats old enough to have developed the fear response did have amygdala activity; and rats whose adrenals were removed prior to developing the fear response did not have amygdala activity. [4] Unfortunately, this study does not appear to have looked at whether rats which were allowed to normally develop the fear response (intact adrenals), but then had their adrenals removed after initial development of the response, still showed amygdala activation. Perhaps that question has been answered elsewhere.

So what does all this mean for dogs? Do dogs have an SHRP? I found one unreferenced assertion that they do, but I have not yet found a study actually examining the canine SHRP. The SHRP does exist in various species, and it seems likely to me that it exists in the dog. Puppies start out fearless, and develop fear later. I suspect that a canine SHRP will prove to be an important part of socialization: the time that puppies don’t yet feel fear may be an important one for introducing them to lots of different kinds of people, so that they can learn that these people are a normal part of puppy life and are not to be feared later on.

The development of the HPA system has been studied in domesticated silver foxes — foxes selectively bred to not fear humans. (These foxes show surprising physical similarities to other domesticated animals in body shape and color, despite not having been bred for these features, leading to speculation that there is some general mechanism of domestication. That general mechanism of domestication is actually what I’d like to get at in a PhD project.) Researchers took two groups of foxes: domesticated foxes, and foxes bred for increased aggressiveness to humans. They tested them for behavioral reactions to humans and cortisol level increases after exposure to humans, at ages 30 days, 45 days, and 60 days. The aggressive foxes did not show aggressive behavior or cortisol spikes at 30 days, but they did show it at 45 and 60 days. The domesticated foxes, on the other hand, did not show aggressive behavior until 60 days, and their behavior at that time was described more as “defensive” than “aggressive.” They never showed the cortisol spike. [5]

Is this the same thing as a silver fox SHRP? I’m not sure that this study exactly gets at that, but it seems suggestive. Questions I’d like to ask about the SHRP in dogs are: Does the SHRP definitely exist in dogs? Is the SHRP length different in dogs and wolves? Does the length of the SHRP affect the socialization of the dog? Is the SHRP length different in different dog breeds? And, most important but most difficult to get at, does length of SHRP have anything to do with a dog’s fearfulness as an adult?


[1] Walker Claire-Dominique, Perrin Marilyn, Vale Wylie, Rivier Catherine. Ontogeny of the Stress Response in the Rat: Role of the Pituitary and the Hypothalamus. Endocrinology. 1986;118:1445-1451.

[2] Takahashi L. K., Rubin W. W. Corticosteroid induction of threat-induced behavioral inhibition in preweanling rats. Behavioral neuroscience. 1993;107:860-866.

[3] Takahashi L. Organizing action of corticosterone on the development of behavioral inhibition in the preweanling rat. Developmental Brain Research. 1994;81:121-127.

[4] Moriceau S. Corticosterone controls the developmental emergence of fear and amygdala function to predator odors in infant rat pups. International Journal of Developmental Neuroscience. 2004;22:415-422. [Free full text.]

[5] Plyusnina I., Oskina I., Trut L. An analysis of fear and aggression during early development of behaviour in silver foxes. Applied Animal Behaviour Science. 1991;32:253-268.