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antipodi
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Joined: 25 Jan 2006
Posts: 1141
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Sat Mar 04, 2006 5:08 pm
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 There be Dragons PtII--dicehalism
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From time to time we hear news of a two headed or dicephalic snake. The condition can and does occur in all the groups of reptiles (snakes, lizards, turtles etc) but while it is known to occur in reptiles that give birth to live young, it is far more common in species that lay eggs.
The fact that egg layers suffer from dicephalism far more than live bearers led researchers back in the late eighties to suspect the condition was not due to a genetic fault , but due to incorrect conditions during incubation.
A species that suffers frequently from dicephalism is the British Grass Snake, Natrix natrix with at least 200 recorded cases.
Researchers noted that the Grass Snake is unusual among reptiles in that to beat the cool UK climate, it takes advantage of the heat generated by rotting vegetation and lays its eggs in compost heaps. Now while a healthy, fermenting compost heap rarely drops below 30 Centigrade (86 Fahrenheit ), a perfect temperature for incubating Grass Snake eggs, in very hot weather temperatures can rise dramatically, even to the point of combustion.
It was felt that these fluctuations were the cause of the problem and so a series of experiments were conducted under laboratory conditions. Researchers found that if Grass Snake eggs are incubated at 30-33 Centigrade, 86-91 Fahrenheit (the average temperature inside a clump of eggs in a compost heap) the hatching rate was about 90% and no abnormalities occurred. If the eggs are incubated at a fairly constant 30-33 Centigrade, but with fluctuations up to 40-45 Centigrade (104-113 Fahrenheit ) mirroring more closely the real environment as recorded by micro thermometers inserted into a clump of grass snake eggs deep inside a compost heap, the hatching rate falls to about 80% and up to 1% of the new born snakes are dicephalic.
Obviously this is something that needs to be kept in mind when incubating reptile eggs artificially. It is important to make sure that incubators are fitted with a good thermostat and that the correct temperature for the species involved is maintained throughout the incubation period.
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