Something I've been exploring recently since getting the Melanistic Diones is the effects of melanism on snakes. The information is very thin on the ground, so some of the observations are from personal observations, albeit only based on a few specimens. I've put together some of my ramblings, hope you find them interesting and would love to hear from other keepers of melanistic specimens of any reptile, amphibian or invert, as to any behavioural/growth differences you might of noticed.


Melanistic Dione

The diet of my Melanistic Diones is no different to any of the others I keep, yet their growth rate compared to some taking similar sized and frequency of meals has a marked difference, they are by far the longest and heaviest. The Melanistic Diones originate from Mostok in North Caucasus so it could be argued that any snake from a colder climate would be at an advantage if its growth rate was excellerated. I have other Diones from this region and their growth rate is no where near as fast.

Also they are the most unpredictable temperament wise, they are real crazy, often gaping and attempting to bite ... very un-dione like ... I don't know if its a melanistic trait ... but I had a pair of melanistic eastern garters ( Thamnophis sirtalis ) a few years back and they were mad heads too as well as a really dark boa (B.c.imperator) which was the devil spawned. On the reverse my Coelognathus radiatus (Radiated Ratsnake) who had a lack of melanin (T+ Albino) were puppy dogs.

I can't find much evidence to back this up, so its only on experience really. What we do know is that melanin as well as giving the snake its colouration, is also distributed throughout the body in certain areas (nerves, brain), although this could be another type of melanin (I don't know). My thinking is, that this increased melanin internally (if it is, the gene may only effect the skin and scales) could have an influence on the behaviour of the snake.

Another observation is their lack of activity, whilst all the other Diones are out playing, these hide away alot of the time, under cover of the artifical plants in their enclosure or inside their hides.

Some experiments have been done in the lab & field on melanistic Elaphe quadrivigata (Japanese Fourlined Ratsnakes) by Koji Tanaka, comparing the data to the normal 'striped phase', interestingly the paper concludes when compared to lab experiments, that melanistic Elaphe quadrivigata do have some thermal advantages because of colouration, but in the wild this was not supported. The reason being is the use of habitat, whereas 'normal' coloured animals would bask on forest edges, giving them a thermal boost, melanistic animals because of their conspicuous colour very rarely basked in the open.


Melanistic Dione

But in a study on melanistic garters, the thermal advantage of melanism was restricted to larger individuals. I'm only guessing but this could be that larger individuals were more confident in basking, or they have different habitat niches at different ages.

With the Black Adder ( Vipera rowan atkinsoni ), results showed they heated up faster in the field but overall body temperature was no higher in day to day living than their normal coloured counterparts. This paper also concluded that either colour exerted only a trivial effect on body temperature of the adders, or melanistc individuals used their thermoregulatory advantage differently, depending on age, gender and *reproductive conditions.


Melanistic Dione

In captivity we control the heat and cover given to the snakes, they have no risk of predation (whether they are aware of that or not I don't know), so can enjoy a readily available thermal gradient environment. where they can likely have the advantage of their colouration in absorption of heat to quickly warm up ... as studies have shown that most melanistic snakes don't have a higher body temperature over the normals, what would happen is they reach an optimal body temperature quicker, which would make them active for longer in the day, burning more calories, so might need a higher in take of prey to compensate for this ... of course on the other hand and the observation I've made with mine, if because of their colouration they felt more vulnerable to predation then they might hide away for a lot of that time and be more opportunist feeders then hunters .. conserving some degree of energy, that when taken over a period of time would account for more growth, compared to other Diones that when hungry will actively hunt.

Going back to my remark on *reproductive conditions. Certainly in the past, breeding of the melanistic phase of Dione in captivity has not been very successful ... one thought that has crossed my mind, is ... we know that incubation temperature has an effect on hatchlings ... now if a melanistic dione warms up quicker, bask longer because of being gravid, would they then have a higher body temperature, would this affect the developing embryos, we already know that, they are well advanced at the point of laying ... just a fleeting thought and one to keep in mind when these are big enough to breed, I think. It could be part of the explanation for the weak hatchlings that have been produced in the past.


Melanistic Dione

One thing I did find, not related to snakes, and its a line of thought to ponder.

In the new Scientist magazine, an article suggested that the simple recessive melanin gene has some health benefits, in that those expressing it are more resistant to disease. This was further backed by research done by the national cancer institute on black cats. They discovered that they were less susceptible to viral infections making melanism an evolutionary advantage.

Also its been suggested it may be a reason why Black Leopards are more abundant in certain areas of Asia because they were more resistant to viral epidemics.

There is also a paper which proves a disease resistance in insects that have a high percentage of melanin ( Melanism and disease resistance in insects - (Wilson et al.)) so early evidence on this seems to point towards this resistance being cross species and not just limited to mammals.

- and on a side note, venomous snakes (Rattlers) have a layer of melanin over the venom gland to protect it against degradation due to UV light .. I've asked in the DWA section if anyone knows of any research done between the potency of normal and albino rattlers/vipers venom, I just thought that was an interesting thought, although if albinism did have an effect it might not be consistent because of replenishment etc.

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I would of thought that melanism would offer an advantage over normal colouration. Surely during breeding they would be quicker off the mark to locate a mate and breed, also as you note in theory you would think they would be more successful while gravid.

There seems to be quite a few populations of melanistic reptiles where they out number normals.

It's interesting to see that the wild observations don't support my thoughts though

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I've not read up on this subject much, nor kept many melanistic animals (the only one I do have at the moment is a melanistic Caspian Whip Snake) but I can offer a couple of my own observations on wild melanistic adders.

I'm fortunate to walk past a heath every day on my way home from work which has a fairly sizeable population of adders, so in the Spring and Summer I can drop by in the afternoons and spend hours watching them. The fact that these snakes are so tolerant of human proximity is amazing, as you can walk right up to them, sit down a few feet away and they will not move - it makes finding and watching them very easy, plus they tend to inhabit specific territories, so you can usually be certain which snakes wil be where at any given time (unless another snake moves in and takes over the territory, which seems quite common in Spring when the males are roving around looking for prime locations - i.e. those with females).

There is one melanistic adder that is always in the same place and I've noticed its behaviour is quite different to that of the "normal" coloured animals. For one thing, it is markedly "shyer" than the normals, which will happily let me approach to within several feet without budging. This one tends to "flush" as soon as it sees you, escaping quickly into deep cover.

Also, while the others spend much longer basking, this one rarely basks in the open, but rather remains cryptic, tending to skulk around the bases of bushes and beneath plants. However, it will return much more frequently to bask - I can only attribute this to it "warming up" much more rapidly in the sun, and the "cooling down" just as quickly when it starts exploring, this needing to return more frequently, but needing less time exposed.

On a similar note, I also notice this animal is active much later than the others, often remaining out to bask half an hour to several hours after the others are no longer visible in the late afternoon and early evening. It was also the last snake I saw this autumn, so it would seem it was able to remain out and about longer than the normal snakes.

This specimen is a male but it is the longest male I have seen on the reserve (it was so big I thought it had to be a female when I first saw it) so that supports Sue's observation of melanistic animals tending to be slightly larger.

Just a few observations as food for thought!

Regards,
Francis

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"There is a pleasure, sure, in being mad, which none but mad men know"
John Dryden, "The Spanish Friar"

very interesting read. something to add to the notes on temperament. i was in a pet shop a few years back and the owner got out an albino black rat snake for me to hold which was incredibly placid and had no inclination to bite. up until this point i had heard that black rats had a bad rep so started speaking to the owner who said that he felt the reputation was quite undeserved, but that he had noticed over the years that the young albino black rats were generally calmer than the normals.

I also feel the reputations of Texas and Black Rats are largely undeserved, I think it stems from the American literature, where of course the authors are used to dealing with WILD examples of the species... even a wild Corn snake will bite! Since the snakes we are likely to see over here are all going to be captive bred and, once out of the "nervous hatchling" phase, I actually find all the obsoletus rats to be among the most docile snakes (and also the most hardy!)

Francis

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"There is a pleasure, sure, in being mad, which none but mad men know"
John Dryden, "The Spanish Friar"

very interesting read. a bit of topic but similarly i had an anery corn that was a nutter ;)

but i didnt think anery was an increase in melanin, but just a lack of other pigments.

After seeing a very dark (poss melanistic) adder this year I done a bit of googling about them. What I found matches your conclusions in your post. Aparently there is site near me where there are more melanistic adders than the classic coloured ones. So from that I take it they are breeding more successfully than the coloured individuals. Going to try and visit the site in the spring so hopefully I will see some more for myself.

There has been a bit of research into the effects of melanism within snake populations, I'm most familiar with the adder literature. Luiselli has a good paper from 1992 investigating the differences in reproductive success, I think there were also some studies from the Scandinavian populations (see Andren or Nilson I would guess). Sorry I can't be more helpful at the moment, I'm just on my way out!

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Regards James Stroud

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