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Welcome back to SciShow Talk Show where Hank talks with Dr. Jeff Good about seasonal animal adaptations. Special guest Jessi Knudsen Castañeda with Cas the Arctic Fox.

Hosted by: Hank Green
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Hank:  Hello.  Welcome to the SciShow talk show, that day on SciShow where we talk to interesting people about interesting things, and about half of our audience clicks on it.  But, the ones that do, really have a good time.  So, thanks to all of you for watching.  

We're here today with Dr. Jeff Good of the Division of Biological Science at the University of Montana, who we have seen before.  We talked to, about rabbit domestication.  You get to study bunnies.  

Dr. Jeff:  Sometimes. Sometimes bunnies.

Hank:  Sometimes other things.  But are they all cute?

Dr. Jeff:  They're all cute.  

Hank:  Right now we have, in the back, something cute, if you can hear that.  I don't know if you can.  A cute thing, that will be joining us later, that is trying to dig its way out of a cage.  So, last time we talked about rabbit domestication, and the marvelous and peculiar process that that was.  But that's, sort of, a side research project for you, that you sort of, stumbled into a little bit.  

Dr. Jeff:  That's right.  So most--  One of the major things--in my lab we study lots of evolutionary procesees--we study how a species come about, and we also study how species adapt to the environment.  Domestication was kind of an interesting sideline in that, and how humans adapt species to their own needs.  But, in the major thrust of the research we are focusing on right now is how species adapt to variable environments.  And so--

Hank:  And so, that sort of the story of all evolutionary biology though, how species adapt to variable environments.

Dr. Jeff:  That's true.  In particular, yeah--  That's what I do.  But the particular problem, that we're interested in, is the places like northern climates, that are seasonally quite variable.  Seasonal variability is very common, in northern environments, where you get really dramatic changes to seasonal environments, you can get very--  Basically, you have to cope in some way.  Some things migrate, some things hibernate, some things basically stay active, but then have to cope in other ways.  

So there's this suite of adaptations that have to go about to deal with these.  And one of the things that we've become really interested in, is animals that change color with the environments, to maintain camouflage.  

Hank:  So you're mostly studying arctic hares, or--

Dr. Jeff:  So we mostly study snowshoe hares.  Arctic hares are a related species that also does the same thing.  We mostly study snowshoe hares, which are very widely distributed across North America.  And they turn white every winter.  Most populations turn white every winter.  And then they turn brown again in the spring.  And that generally tracks to local onset of snow cover, and the persistence of snow cover.  

Hank:  So, as a camouflage?

Dr. Jeff:  As a camouflage thing, but the really fascinating thing is that that period. We live in Montana, as you know, you know that the snow can come earlier or late, and it can be a lot or a little.  Some years, not at all.  That period of variability, it turns out, is really crucial for the hares.  And so, their turning color, to kind of track this general cue in the season changes, which is driven by how much daylight there is.

Hank:  So that's the trigger?  It's not temperature.  It's not--

Dr. Jeff:  Most seasonal changes are primarily driven by changes in how much light there is, called photo-period, how much daylight there is.  And it triggers different hormones, that trigger a suite of changes, though.  Whether or not you're reproducing, whether or not you're active, whether you're choosing to migrate, things like that.  In this case, the seasonal molt, which includes growing out new hair, not just changing the color in some cases, but also changing the insulation of the hair, as well.  The overall characteristics of the hair, putting on that winter coat, that you can think of.  Like that dog, that puts on the heavy winter coat.  

In this case, this is controlled by photo-period, and it's tied to color.  So, the daylight's the same every year, some years there is very little snow.

Hank:  So you could take a hare, and put it in a lab, and give it a daylight cycle, have it never change?

Dr. Jeff:  Yeah, that's right.  That's right.  And so we actually have-- We study two species that do this.  We also study dwarf hamsters , which are another naturally, seasonal changing species.  So, it's the only hamster that changes, native to Siberia.

Hank:  Would a person who owns one of these hamsters have any idea that that would happen, because they're keeping them inside all of the time?  

Dr. Jeff:  Yeah, well, if they don't have them under constant light, then they will change.  And so if you go--  There are domesticated versions of this, they're called Russian whites, that if you have them on short days, usually less than twelve hours of daylight. What happens is this does of hormone, melatonin that actually makes them do this shift, then they'll turn white.  And depending on how consistent the light is, and the darkness of the light, they'll turn all the way, or not.  If they get a lot of variation in the light, then they will... And the same thing is with the snow shoe hares.  There's other things that modify it, like temperature, but we don't really-- The main thing is photo-period.  

Hank:  So it does have multiple inputs there.  

Dr. Jeff:  Yeah, multiple inputs.  Primarily driven by--

Hank:  That sounds, like, a tough nut to crack.  So do you see--  So you would then see across the population, you know more northern species--  If you took a more northern species and put it more southern, would it basically, just, because the daylight period would change?  So, would it--  Is there, like, genetic variability there?

Dr. Jeff:  That's a great question.  We don't fully know the answer to all of that.  It's part of what we're interested in studying.  We know that if you take extremes, so in some cases, kind of two cool things.  If to change color, and when to change color.  So. snowshoe hares live across North America, and all the way up from Alaska, all the way down to here, in Montana and even further south.  

And so, when you might want to change, is, can be quite different along that gradient.  And also along the coasts where, perhaps you don't get as much snow cover.  So the "when to change" kind of tracks north-south gradient, and it's true, things turn earlier late and stay longer, stay white longer.  And then further south, there's a gradient on that.  The genetic basis of that is something we're really interested in.  We're trying to make end roads on that, but it's kind of a tricky, trait to study.  

Another cool thing is "if to change", and that also has geographic patterns.  So some species, or some populations in snowshoe hares and other species that also turn white, have local populations that have lost the ability or no longer turn white, or stay brown all winter.  And that usually occurs in places that snow cover is much more intermittent.  

Hank:  So coastal population.

Dr. Jeff:  Coastal areas.  So we're particularly interested in the populations of snowshoe hares that occur along the West Coast of North America, so into Washington, and Oregon, and to BC.  And in those areas along the coast, they stay brown all year, and then inland they turn white.  In the middle, there's a mixture of hares that are white and brown in the winter.

Hank:  So it seems like the kind of thing that would have a more minor change that would lead to uh, a simpler change in the expression of the gene.  

Dr. Jeff:  So there are, we kind of distinguish between things that are big changes and little changes, depending on how much they change.  You know, the trait you're looking at.  In this case, it's a pretty striking change, so it goes from white to brown.  We think it has a simple basis, but it's a big change.  So, not always the big changes aren't always mini, many genetic changes.  

And so they're kind of two separate questions that we're interested in both of them.  But, we think that at least the "if to turn", is something that has a simple genetic basis and is controlled by one or two genes, we think, right now.  And so, but, whether or not that has to do with when and how those genes are turned on is the question.

Hank:  So, one last thing here.  If we're talking about this snowshoe hare population that isn't changing, how might that trait have arisen?  Aside from the fact that the environment doesn't require it, so maybe it's extra energy that doesn't need to be expended?  But how would that trait have even been created or introduced?

Dr. Jeff:  Right, so a simple scenario would be snowshoe hares living mostly in areas where they need to turn white , but then they colonized these coastal areas, that where it's no longer a good thing to be a white hare in a brown world.  And so, new mutations arise, and those mutations influence the trait, and so the hares that stay brown in the winter survive more, and then that trait spreads locally and fixes.  So, that's kind of the new mutation scenario.  

Another possibility that we're kind of intrigued by is in this particular population that stays brown, it also shows a history of hybridization with a species of jack rabbit that's nearby.  And it's possible that some of the genetic variants, that underlie this trait come from the jack rabbits that don't turn in the winter.  But that's--

Hank:  That might, sort of be, a shortcut to getting there.  

Dr. Jeff:  Yeah.  I mean, it would have come from mutation ultimately in the jack rabbit as well.  But the really interesting thing, and one reason we're really interested in the trait, is that it turns out the "when to change" is really, probably, going to matter under most models of climate change.  So the major--in temperate areas we think about all the things that might happen with climate change.  In temperate areas, the single, largest trait that you see, environmental trait, that you see associated with climate change and predicted shift is actually how much snow cover there is.  It's not temperature and precipitation, per se, but how much actual snow cover there is, with all the predictions being less and less.  

And it turns out, at least local populations, so a colleague of mine Scott Mills, whose at North Carolina State University.  He's been studying snowshoe hares in Montana for twenty years, in some of these population cycles.  What he's shown is that it turns out to be really bad news to be either a brown hare in a white world or a white hare in a brown world, and it dramatically drops their mortality, or their survival, through a lot of predation.  I mean, everything eats hares.  That's pretty much how they die.  No hare dies of old age.

And they pretty much get eaten.  And they get eaten a lot when they're the wrong color.  And so the amount of time that they're the wrong--  They're changing at the same time every year, but the amount of time that they're the wrong color can change under different laws of climate change.  And so, we of course expect there to be a biological response to that.  We don't think it's just a static trait that all the snowshoe hares will go extinct or something.  

But there is this question about how quickly can it change, how will it change, what is the mechanism underlying that?  And the details of the genetics really matter for understanding what, if they could change under really quick scenarios, where suddenly there's no snow or something.  

Hank:  That's really cool.  I feel like that conversation was very information dense and very interesting, so I--

Dr. Jeff:  Well, good.  Because those aren't always the same thing, right?  

Hank:  Yeah, but now I think that we are going to get to--  So thank you for sharing that.  Really cool and it's just always really fascinating to hear about the practical everyday stuff that's going on all over the world.  And we're so lucky to have cool people studying cool things really nearby, where we create SciShow.  So thanks for sharing.  

Dr. Jeff:  It's great to be here.  

Hank:  But now, we're going to now see an animal that actually does this.  And it's summertime right now, so this will not be a white animal.  But it will be in just six months time.  So let's introduce our friend.  

Hank:  Alright, we have returned.  This is Cas.  This is Jessi.

Jessi:  Hi!

Hank:  Cas is the--  Has the emotions I've seen in every fox I've ever met, which is a mixture of extreme curiosity and anxiety.  

Jessi:  Yeah!  Well, yes, yes.  

Hank:  Like, I want to know everything, but also I'm terrified.  

Jessi:  Yeah.  That is exactly what almost all foxes exhibit.

Hank:  So, Cas is, uh, right now pretty white actually.  Whiter than I was expecting.  

Jessi:  Yeah.  We saw him two and a half years ago , so it was January when we saw him and that is going to be the winter, heavy deep winter.  (Hank:  This is--)  Yes.  Exactly.  That's all of his winter fur, right there.  How soft is that?

Hank:  It's very soft.  I could make a sweater out of it.  And also just leave it all around this room for the other people who use this room to enjoy. 

Jessi:  So, he started molting into, or shedding, into his summer fur, about three months ago.  And this is-- He's four years old.  And this is actually the first time he hasn't completely shed out .  He still is retaining some of his winter fur on his tail, there.  But all of this is his summer fur.  That's actually the thinner, coarser, summer fur and so it's kind of interesting to us.  We haven't seen this "silvering".  He's usually a very dark grey fox, at this point.

Hank:  Huh.  So they really do get a whole new coat every year.  

Jessi:  They do, yeah.

Hank:  And this coat is different than last year's.  

Jessi:  It is.  It's different from the last three years.  

Hank:  Explain!

Jessi:  Yes.

Dr. Jeff:  Well, I don't know. You said you saw it before.  Sometimes it requires both the light cue, but also the temperature cue.  And environment in general, so food and grass, and all those things can affect his traits.  So, in some species, you can't actually get the trait to induce in a controlled environment.  So, I don't know why he not changing.  It could be an age related thing, too.  But typically, they change.  But it's interesting that you say he's molting.  You can see he's got the--  He's molting out the insulated, under fur.  

Jessi:  Yup.

Dr. Jeff:  So the key--  It's not just changing the colors, but you also--  If you look at them; the audience can get the profile, but you can actually see these kind of bristly things sticking up.  Those are called guard hairs.  Very long.  And then there's intermediate hairs, called the on hairs, usually, and those are what give visible color, usually.  And it's the tip of those that would make most things white, or brown, or whatever.  And then underneath, you would have this dense wool that is necessary.  The other thing you have to deal with in the winter, which is being very, very cold.  So these guys can live in incredibly cold environments.  What time did he change?  

Jessi:  This year?  It was about three months ago.  So, April.

Dr. Jeff:  So he started changing in April, and then in the winter he starts to change in September?

Jessi:  It's October.

Dr. Jeff:  October.  So, I think in the wild, they--I think it's shifted more September and May.  That's my understanding at least, in Alaska.  And so it could be that there's an interaction between the light, or also the amount of temperature.  

Jessi:  It's not getting as cold here in Montana.  So why--

Dr. Jeff:  It could be, also, we had pretty--

Jessi:  We did have a mild--

Hank:  A mild winter--

Jessi:  Yeah, a mild winter and it got hot really fast.  But you think that would change it--  But then, it got cold again.  It's been a really weird year.

Hank:  We've had really weird weather this year, trust me, just in general, which can be explained by different types of scientists, I'm sure.  

Dr. Jeff:  Not much to say about it, other than it was hot.  

Jessi:  So I was also interested, because he's now four years old and they mature at about two years old in the wild.  But at two years old, he was very hormonal.  Intense. And at three years old, he was still kind of hormonal, but this year, he has just really mellowed.  And so, I was wondering if the hormones came into play with the expression of that change?

Dr. Jeff:  Well, the traits-- The hormones that drive the color change are also the same ones that interact with things like reproduction.  And so, melatonin is the hormone that gets turned on when it's dark, and so that's why you take melatonin when you want to reset your sleep schedule.  Because your body gets that cue when it's dark, melatonin is released.  The more dark you have, the more melatonin, then there's this threshold at some point, where you start to trigger all these other things.  

So, like, the molt, and for a lot of species, shutting down reproduction, because you don't want to reproduce in the winter. And change in a lot of other things, like how you stay warm, fat reserves, and the types, and how you store things.  And then in the spring, the melatonin gets down weighted and you start to get prolactin, which is the other major hormone, coming on that drives a lot of the-- Does a lot of things, but is pretty heavily involved in reproduction.

Hank:  Cas, you're being really good.

Jessi:  He's being amazing.

Hank:  We were a little nervous about this. 

Jessi:  We weren't sure how long he was going to be able to tolerate-- You know.  There's three people here.  There's a new table.  Well, there's not three people here, there's lots of people here.  But there's three close people and all these lights.  We had him on two and a half years ago and he didn't last this long.  He's doing quite well.  He's panting.  He's hot.  He's a little bit nervous.  He's not showing me that he's really stressed out.  He's baseline right now.  

Hank:  This is how foxes are.

Jessi:  This is how he is.  We can talk about other adaptations, though.  Under their feet, their pads are not bare.  

Hank:  Oh really?

Jessi:  Let's see.  I don't know it you can actually see the pads of their feet.  Look at the back feet too.  They have--  They're covered in fur and in the winter it's going to be even bigger.  Ooh.  I'm sorry buddy.  Ooh, sorry buddy.   Slippery table.  Got it?  Ok.  
Hank:  He's just relaxing.   So they have, especially in the winter they have like a mitten?

Jessi:  It is!  It's like a big pad underneath there. (Dr. Jeff:  Like Hobbits.)  And it's for thermo-regulation, but it's also for--  This is amazing I think (Hank:  So much hair.)  It's also for traction.  It didn't work very well on this very smooth table, but when he's running on ice and snow, it's going to give him a lot of traction on that.  

Hank:  Like little snowshoes. 

Jessi:  Yeah.  exactly.  And their feet are very big.  

Dr. Jeff:  Snowshoe hares have very furry feet.  And so do the hamsters.  The little hamsters that we study, that are native to Siberia, and they're active.  Not nearly as cold as these guys go, but they can be active down to -30 degrees Celsius, and they have furry feet as well.  They have, like, really furry little feet.  And they're very--  They don't--  When somethings in a lot of cold places, they don't have as long ears, not sticking out. 

Jessi:  Shorter ears.  Shorter nose.  

Dr. Jeff:  Furry feet.  

Jessi:  Shorter legs.  Poofier tail.  I'm going to go ahead and put him back.  He's trying to show me "he's done now".  

Hank:  "I'm done now."

Hank:  So, we're now all covered in hair.  I've just realized that I'm allergic to arctic fox.  

Jessi:  Well, that's a pretty cool thing to be allergic to.  

Hank:  Right.  Yeah, I mean, I'm not going to run into that problem that often.  You have to go away, because you are covered in it.  

Jessi:  Shake off outside.

Hank:  But, thanks for showing off Cas.  This is Jessi of Animal Wonders.  And if you want to check out her Animal Wonders channel it is  This is Dr. Jeff Good of the University of Montana, at the Good Laboratory, which you run.  

Dr. Jeff:  Yeah.  I named it.  

Jessi:  You did a good job.  

Hank:  Thank you for watching.  Thanks for hanging out with us here on the SciShow Talk Show.  If you like this, we are happy to make it for you, but we are only able to do it because of our supporters of Patreon.  If you want to learn about that, you can go to  Do you guys have a Patreon?

Jessi:  We do.  

Hank:  Where's your Patreon?

Jessi:  On Patreon, Animal Wonders Montana.  

Hank:  So it's  It's on Patreon Hank.

Jessi:  No, it's just Animal Wonders.  We'll put a link in the description.  And if you want to keep watching this stuff, we appreciate that, and hopefully we will keep making you smarter.  You can go to and subscribe.