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I get a lot of emails from people looking for information on hognose snakes and a lot of it ends up being questions like "what species is this?" or "are hognose snakes venemous?". However, occasionally I get a really interesting email and a recent one got me thinking about death feigning in hognose snakes. The email was from someone curious about the notion that death feigning in hognose snakes was a model of epileptic seizures. The source of the question came from a couple of pages in a book called Medical Herpetology by Steve Gerard.

The main gist of those few pages was that death feigning had a lot of similarities to epileptic seizures that you see in humans beyond the outward appearances of it. For instance, the levels of adrenaline are elevated in both epileptic patients during a seizure as well as hognose snakes (no data given) during death feigning as well as rattlesnakes when they are rattling their tail.

For the most part I told the person that this was an interesting observation but that I had my doubts about it being linked to epileptic seizures. However, it is an interesting suggestion considering that all of the cases of death feigning and tail rattling (broken down as ‘muscle spasms’) are stress related situations.

Below I have copied and pasted my resoponse to this person...

Anyway, I think the author makes a compelling case for hognose snakes as a seizure model but I think ultimately it is all speculation.

So in my opinion, the origin of these behaviors may have a basis similar to that found in epileptic seizures but that they may not make a very good model today even with the similarities. Epileptic seizures are still a neurological ‘problem’ in humans and so may not be modified in the way you would expect in organisms that have used the behavior for survival.

While I was very skeptical in my email the idea that a stress-related mechanism is what drove the evolution of death feigning and tail rattling is very very intriguing to me. It has always bothered me that death feigning seems to have such little survival value yet is a very common response especially in certain parts of the H. nasicus population (although is very uncommon in other parts). The large adrenaline glands in Heterodon (as well as some other snakes) does seem to suggest that the initial responses to stress of increased adrenaline and muscle spasms could have easily led to the behaviors of death feigning and tail rattling.

Anyway, I thought I would throw this out there and see what all of you thought of it.

Curtis

Curtis,

An interesting hypothesis, but I am not sure I buy it. If death feigning was a totally physiological response, I doubt Heterodon would be able to turn themselves back over in response being "righted". Furthermore, the fixed action patterns that Heterodon undergo during their "death" seems too programmed to be explained by erratic neurological impulses (epileptics don't all move the same way during seizures).

It is an interesting question whether Heterodon (or Natrix, Hemachatus and other death feigners for that matter) would respond to increased adrenaline by death feigning. You could grind up some hognose adrenals and inject the slurry in other hogs and see how they respond !

The selective nature of the hogs response also seems to contradict this. If it were a simple physiological response to stress hormones, wouldn't an exaggerated food response also stimulate the "seizure"? Epileptics can be "set off" by a variety of stimuli. Hogs seem to have the ability to choose their response.

Chris

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Chris Harrison
Central Texas

(Preface: I want to thank Curtis for posting his thoughts on this forum. It is great to get some discussions that deviate from the norm!)

Death feigning certainly has been debated in the literature, everything from a psychophysiological origin, to a purely voluntary response. In a popular discussion, a view was expressed that death feigning "may be brought on by the effects of specific chemical substances diffusing from nervous centers; such substances would be destroyed eventually bite and semantic, oxidative, or other processes".

I begin with:
Burghardt, G. M. 1991. Cognitive etholohy and critical anthromorphism: a snake with two heads and hognose snakes that play dead. In Cognitive Ethology: The Minds of Other Animals. 53-90.
In this chapter, Burghardt does an extensive review of death feigning including going back as far as quoting Darwin on multiple occasions, who apparently spent quite a bit of time on the subject himself. Burghardt describes the different mechanisms and synonyms of death feigning (preferring the term "tonic immobility", and much like the hibernation debate, mentions what is true death feigning.

What Burghardt considers interesting with hognoses is that they add "both a vigorous and aggressive but innocuous bluff attack phase in a dramatic 'death' prior to the death feign. It is highly possible that the hognose display is an evolutionary elaboration and ritualization of response elements occurring prior to the immobile phase with the feign itself being derived from restraint induced tonic immobility".

This hints upon Curtis's theory on a stress induced tonic immobility. However, despite there being some physiological similarities with death feigning in hognoses and epileptic seizures, I think the similarities end there. The most profound difference that is exhibited in hognoses is that this behavior is entirely voluntary. On top of that, since hognoses flip themselves back to upside down when rolled over, it implies that hognoses are somehow aware of their behavior in terms of its purpose and ultimate goal. Think about that one for a second. If the previous statement were actually true, it indeed would be profound given the assumed cognitive ability ethologists (and most people) assign to reptiles!

Building upon the statement by Chris Harrison on the selective nature of the death feigning response, Burghardt and Harry Greene carried out extensive tests of adult and hatchling death feigning behaviors. They noted that the stimulation needed to induce the death feigning response actually declined over 40 days, which is contrary to most herpetoculturists observations. Recovery time from the death feigning declined. There was also a large variation in the exhibited behaviors, everything from the sequences of the death feigning phases, to the degree of death feigning. I think the difference here is that these animals were not truly in captivity where they would be desensitized to human presence. Nonetheless, Burghardt considered the observed increase of death feigning to be "conditioning to the stimulus and habituation of the recovery phase". The terms "conditioning" and "habituation" don't seem like words used to describe something physiological much less something involuntary. Perhaps the individual variations observed for this behavior may indicate that the individual may have some "control" over how much of the death feigning behavior they want to exhibit depending upon the situation; similar to the control of the amount of venom used in defense by venomous snakes.

Burghardt goes on to provide some insight into hognose behavior with sections titled "Further Consideration of the Magnificent Hognose Display", "Intentionality in the Hognose Snake", "Decision-Making", and "Premonitions of Cognitive Ethology". Clearly, this is a must read for anyone interested in the subject.

Another paper is essential for this discussion since Chris Harrison mentioned injections of adrenaline:
Edgren, R.A. and M.K. Edgren. 1955. Experiments on bluffing and death-feigning in the hognose snake Heterodon platyrhinos. Copeia.
In this paper they tested some neurological stimulants such as nor-epinephrine, acetylcholine (ACh) and epinephrine by injecting them into eastern hognoses. The results suggested that the defensive behaviors of eastern hognoses are not mediated by these chemicals, apparently even at very high doses. The observed spasmodic respiratory movements, heavy salivation and jaw movements (poor guys) are typical signs of ACh stimulation. The Edgrens stated that the behaviors are not dependent upon the adrenal medulla, or the parasympathetic nervous system (if anyone can provide insight on this last sentence, please post). Lastly, the authors state that is probable that the defensive behaviors of hognoses are best "considered as central humoral or reflex effects".

Eckerman: I am curious about your statements about death feigning not truly being evolutionary advantageous. Certainly in theory death feigning has an incremental advantage, is there empirical evidence to support that it is not?

In conclusion, I'm personally inclined to give hognoses more credit for their derived and unique behaviors. I have a strong feeling that hognoses are not slaves to their instinctive defensive behaviors, although they certainly do act extremely unrefined and barabaric sometimes. Unfortunately I think this is another classic case of hognoses being so fundamentally different from other snakes, coupled with the lack of research on them, that we are left scratching our heads. Unfortunately, my literature collection on hognose death feigning is scant compared to what is available, I wish I had more to add to the discussion.

Here are some quotes I find interesting from the Burghardt paper:
"Attempting to deceive one's harasser is a risky strategy and paying close attention to what the predator is doing might be critical."
"Deception in animals is considered one of the highest accomplishments of animal cognition. By focusing on fear as an explanation for immobility, psychologists and ethologists have missed the possible cognitive aspects of tonic immobility in general, and death feigning, the ultimate deceit, in particular."

I have always liked this description by Charles Myers of the hognoses tendency to roll back over;
"It is characteristic for a 'lifeless' hognose snake that is placed on its belly to roll over again, as though this were the only respectable position for a dead serpent".
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"I know the human being and fish can coexist peacefully."
Governor George W. Bush, Jr.

"Sometimes I think the surest sign that intelligent life exists elsewhere in the universe is that none of it has tried to contact us."
Calvin and Hobbes (Scientific Progress Goes 'Boink', 1991)

Burghardt describes the different mechanisms and synonyms of death feigning, preferring the term "tonic immobility", and much like the hibernation debate, mentions what is true death feigning.....The most profound difference that is exhibited in hognoses is that this behavior is entirely voluntary.

I don't know that I agree with the idea of hognose death feigning as any sort of tonic immobility. Hognosed snakes perform what could better be described as "flaccid immobility".

On top of that, since hognoses flip themselves back to upside down when rolled over, it implies that hognoses are somehow aware of their behavior in terms of its purpose and ultimate goal. Think about that one for a second. If the previous statement were actually true, it indeed would be profound given the assumed cognitive ability ethologists (and most people) assign to reptiles!

I don't think you have to assign any sort of cognitive awareness of the "goal" of the behavior in order to explain the fact that they will turn back over. It is simply a fixed behavioral response that they "need" to be upside down when playing dead.
If you want to discuss cognition and awareness of the effect of the sham, you could argue that the "reinversion" is evidence of LACK of cognitive understanding. It certainly gives away the ruse!

Burghardt and Harry Greene...noted that the stimulation needed to induce the death feigning response actually declined over 40 days, which is contrary to most herpetoculturists observations. Recovery time from the death feigning declined.

I have observed the same thing in captive born nasicus. The first time you try to get them to feign death, it takes a little effort (I was getting them to play dead to try and get them to eat pinks). The next few times, they were much quicker to flip, although they were also quicker to recover, as B&G observed.

Generally, in captive situations, we aren't trying to make them flip so we don't deliberately torment them, which is what I was doing and what they were doing.

In this paper they tested some neurological stimulants such as nor-epinephrine, acetylcholine (ACh) and epinephrine by injecting them into eastern hognoses. The results suggested that the defensive behaviors of eastern hognoses are not mediated by these chemicals, apparently even at very high doses.

Interesting. Further evidence of this being a completely behavioral response, not a chemically mediated response.

The Edgrens stated that the behaviors are not dependent upon the adrenal medulla, or the parasympathetic nervous system (if anyone can provide insight on this last sentence, please post).

First of all, adrenaline and epinephrine are the same chemical. Adrenoline is a secretion of the adrenal medulla, therefore the lack of appropriate response to doses of adrenoline indicate the adrenal medulla can't be stimulating this behavior. Norepinephrine is a neurotransmitter secreted by parasympathetic neurons (as is epinephrine) so the lack of response to this indicates no involvement of the parasympathetic nervous system.

Deception in animals is considered one of the highest accomplishments of animal cognition. By focusing on fear as an explanation for immobility, psychologists and ethologists have missed the possible cognitive aspects of tonic immobility in general, and death feigning, the ultimate deceit, in particular."

Again, I disagree with the characterization of this feigning as tonic immobility.

Then there are the uncommon incidences of death feigning in Coluber and Masticophis...hmmmm, the plot thickens.
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Chris Harrison
Central Texas

In this paper they tested some neurological stimulants such as nor-epinephrine, acetylcholine (ACh) and epinephrine by injecting them into eastern hognoses. The results suggested that the defensive behaviors of eastern hognoses are not mediated by these chemicals, apparently even at very high doses.

Interesting. Further evidence of this being a completely behavioral response, not a chemically mediated response.

Well this is where I will admit a certain amount of ignorance. While I understand very well the effects of neurotransmitters and hormones in humans (it's what I get for volunteering to teach Anatomy and Physiology) I'm not completely sure that the chemicals in reptiles are exactly the same.

Also, it seems to me that just because the chemical is injected that wouldn't necessarily mean it should induce the response as long as it isn't completely chemical induced. And I suppose I should clarify here as well. In my previous post I was talking about the origination of the behavior and not how the behavior has changed to what we see today. But I still have some misgivings about such an experiment. For example, you could inject nor-epinephrine into a human and blood vessels would dialate going to the muscles, your heart would increase in rate and force and a whole slew of other things would happen but if not produced with an outside stimulus you won't have the actual 'fight or flight' response. It will just continue to feel like you just got done with a fight but not actually make you just start fighting someone at random.

So I think maybe there are two questions that are being addressed and I have to be careful to separate them. The first question I meant to raise was how the behavior originated and this is actually a different question (althoug very related) to the question of how the behavior is stimulated and controlled today.

Again, just a very interesting thought question.

Curtis

Hey guys, thanks for responding.

Hopefully you saw that I am very skeptical of the comparison of death feigning to epileptic seizures as well. However, the idea that the behavior has a stress-response underpinning is very intriguing.

First, as far as I know there has been no rigorous study of the advantage of death feigning in hognose snakes regarding how often it proves to be advantageous in nature. Not that there isn't an advantage but the extreme variation in the frequency of this behavior between species and even within species makes me suspect that the actual selective advantage of this behavior may be very slight. Again, i'm not saying there is no selective advantage because the behavior obviously exists. However, it just makes more sense to me (and thus my totally unfounded opinion shows its ugly head) that the behavior has an origin originally unrelated to death feigning. I guess what I'm getting at is that in order to avoid a circular argument you have to look for other reasons why this behavior would have originated and then later become co-opted to enhance a particular behavior.

I think that the 'embellishment' of a stress related behavior in hognose is similar to how rattlesnakes have also responded. So many snakes actually have similar, albeit less fantastic, behaviors when it comes to tail rattling and death feigning.

If this is a stress-chemical related response then it also explains why hognose snakes will lose this behavior in captivity. Once a stimulus that induces stress becomes common then the response declines.

It is evident that the hognose snake and even rattlesnakes have some control over this behavior but I don't think that necessarily means that they are concious of the manipulation of this behavior.

I would think a pretty easy experiment could answer some of these questions. Like chemical assays from those snakes as they produce the behavior versus those that don't. Or even look at adrenal glands (as well as others) in parts of the population that produce this behavior more readily compared to the areas that don't. Heck, even experiments on snakes as they lose the behavior in captivity might answer some of these questions about its origin.

Anyway, I'm totally speaking off the cuff here and appreciate some of the references you put up. I'll hunt them down and see what they say in detail. Sometimes I get these quirky ideas in my head but there aren't too many hog-heads up here in Iowa so I thought I would use this forum.

Now that I'm settled into my new job i'll have more time to spend some time here with fellow heterodon lovers

Curtis

-"It can't be a very good Psychology book if people understand it." - Pepperment Patty