2 headed Diamond Jaguar!!!

[gonesnakee]

Well I had what I thought was just a dead Diamond Jaguar (50% Diamond 50% Coastal) left in the egg in the incubator. Figured I better get on tossing it, but decided to have a look at it first. Boy was I ever surprised to find it had 2 HEADS There were also 2 sets of twin "siblings" that did make it in the clutch. The doubleheaders heads were at the bottom of the egg when I cut it/them out. Very wild as we were just discussing twins & doubleheaders earlier in the day on the Edmonton Reptile Forums. Crazy! Mark

members.shaw.ca/gonesnakee/JAG2HEAD.JPG

members.shaw.ca/gonesnakee/JAG2HEADS.JPG

[alex]

Cranioaxial duplication is a really, really common birth defect in snakes. It's quite well reported in scientific and lay literature 'cause everyone likes two headed things. I wrote up a case of it a few years ago and the most common teratogen identified is temperature - too hot/too cold during incubation (or gestation in viviparous species). It's interesting too because so many of the cases are quite similar - probably a result of the really simple snake body plan leaving very little room for obvious deformations, but still - snakes seem to go two headed, lizards more commonly have two tails. Most seem to die in ovo/in utero, and those that make it to hatch/birth have a really high mortality rate, probably due to biochemical and neurological changes that are kind of subtle to evaluate. My case had a really awkward locomotion that indicated some sort of neurological issue (though the cardiopulmonary and intermittently gastrointestinal duplication was probably more immediately lethal).
Twinning is more likely to be the same sort of thing as with avians - two eggs being released close together and getting incorporated into one set of embryonic membranes.

[gonesnakee]

Well I have to disagree on the really realy common comments as it is not. It does happen but is far from common. It may seem that way because so many snakes are bred yearly in NA but percent wise it is in most all likelihood less than a tenth of a percent likely less than a hundreth of one IMHO. Best person to talk to would be Van Wallach PHD down at Havard. He was the one that did the Reptiles Magazine artiicle a few years back now. As for my case being a birth defect caused by temps I have to disagree there as well. Very obvious to me that it was just a twin gone "wrong". No deformities in the whole clutch except the double header & stable temps thru out entire incubation. Same clutch had 2 other sets of twins & the same male fathered twin Diamonds this year as well. When I had my female 2 headed Lavender Albino CK the same pairing produced twin girls another year & the same male bred to a different female produced twin girls again as well. IMHO I think there are genetics involved resulting in these twins, not deformities caused by temp spikes etc. Cheers Mark

[alex]

I said really common birth defect - which does imply rarity, at least to me. I realise I probably come from a slightly different background as a DVM and PhD candidate pathologist and perhaps I should've phrased it better in the first place but I almost never talk to clients anymore. Birth defects as a group are still a low percentage of all live births. It's like saying patent atrial septa are a common birth defect in people. I actually have talked to Vin Wallach - he got in touch with me over the paper a few years ago. I haven't read Reptiles magazine since I found it became disappointing to me right about the time I started having to haul all my stuff around Canada every few years, but I don't recall my paper being in conflict with anything he and I discussed. I've got an extensive lit review somewhere, if you'd like me to send you the references. I might need reminding, because all the papers I moved to Ontario are all still sitting in boxes waiting to be sorted into files in drawers again (somehow, there's always something better to do... like actually going outside). A lot of the papers are quite old, so you'd likely need access to a decent university library to read them all. No one has concrete evidence (as the frequency of total birth defects is low, it's difficult to induce experimentally even with relatively high frequency defects) but the majority of cases are linked to improper temperatures, especially in the viviparous snakes I was writing up.
While there is evidence of genetic twinning in humans and a few other animals, I'm not ruling out the possibility in snakes but evidence suggests it is similar to the mechanism in birds. It's a common phenomenon in the poultry industry and is generally considered a byproduct of breeding for frequent egg laying. Twinning offers almost no selective benefit to the egg laying amniotes - the egg is a confined space with finite resources, and identical twins don't really offer significant benefit outside of fairly static environmental conditions (i.e. other parthenogenic XY reptiles - doesn't really work with ZW's, and many boids appear to be TSD anyway). Twinning produces smaller offspring and potentially compromises the growth of both - you can see this effect quite well in different mammals - there are reproductive features of sheep or deer that make twinning an acceptable strategy, but twinning in horses is extremely difficult and rarely results in two live births due to the shape of the uterus and placentation. The genetic influence may not be on actually producing twins per se, but rather the frequency of ovulation and the number of eggs ovulated per ovary - typically snakes alternate ovaries, but if eggs were released simultaneously (from either ovary or from one) you would have two eggs entering the rest of the reproductive tract more or less simultaneously, and being wrapped in the embryonic membranes and entering the shell gland simultaneously. This, sans the whole eggshell thing, is almost exactly what happens in euplacental mammalian twins, as fraternal twins are by far the most common. It's further backed up by the extremely infrequent incidence in twinning in anamniotes - twinning in those species only occurs by monozygotic means. I've never seen anything to suggest twinning in reptiles is temperature related, I thought I kept the two separate in the post above and I apologise if it was confusing. I meant to discuss two separate phenomena in the post above.

[gonesnakee]

No worries & I have also had what you were refering too in a clutch that was subject to temp spikes issues. One clutch of striped corns had many eggs go bad & many other malformed stillborns & kinked babies. The one in particular had a split head & 4 eyes, likely the condition to which you were refering. It died very soon after I manually pipped it. Cheers Mark