A large amount of the information contained in this document is available from various sites on the Internet, but very little of it has been listed on one site at the same time. Another part, and possibly the most important, was gleaned from research done by Dr. David Chizar, Dr. Hobart Smith and others as they tried to explain separate instances of unusual reproduction in reptiles. We'll discuss this a little further down in the article. Let's just say that their findings were controversial and enlightening at the same time considering that while the herping community knew a great deal about some animals, there was virtually nothing known or understood about others. Once you grasp the depths of their studies, the rest seems to fall into place. I won't try to quote them, but let me give them credit here for the outstanding work they did in making the unknown known and understandable.
Generally, when determining the male/female ratio when temperature sexing, cooler temperatures result in higher female production while warmer temperatures result in higher male offspring being produced. The strange thing about this can be found in Leopard Geckos where even higher temps can result in more females being produced, but quite often they are sterile and will not reproduce as they mature. This is often the result of accidental overheating of the incubator or, all too often, the way breeders supply pet stores for relatively low prices. The eggs hatch faster at higher temps, so when breeders are looking to hatch a large number of eggs in the fastest time possible, for quick money in the neighborhood pet supply business, these higher temps pose no obstacle or threat to their continued income.
More data needs to be collected, over long periods of time in order to determine just how broadly temperature sexing of eggs extends. The unfortunate part of this is that too many people breed their animals, incubate their eggs in the safest (and most efficient manner) and raise the offspring systematically so as to not run any risk. The risk mentioned here is the loss of offspring and money, which can sometimes be used to restock the food supply for the parent animals later. Until more breeders are willing to take risks with offspring and their possible income from offspring, keep detailed records of every little event in their pet’s life and report all of the results, good and bad, then the current information available on reptiles may never be updated which would allow us, as their keepers in captivity, to take the best possible care of them so that they can live their lives to the fullest.
In humans, scientists code these as “X” and “Y” chromosomes. Female humans have 2 “X” Chromosomes and must provide an “X” for reproduction. Male humans have an “X” and a “Y” chromosome and so may provide either for reproduction while never knowing which. By this method, it is the human male genetic material that determines the gender of the offspring.
Research by noted scientists such as Dr. David Chizar and Dr. Hobart Smith, among others, has determined that the genetic make-up in snakes, at least some lizards, and possibly all reptiles, is the opposite. Their findings were finally published in an early issue of Fauna magazine along with another startling discovery we will touch on shortly. They determined that the chromosomes for snakes, which we here will label “Z” and “W”, are found in just the opposite situation. Specifically, females have the different chromosomes (1 “Z” and 1 “W”) and ultimately determine the sex of the offspring while the males (2 “W” chromosomes) simply provide the other half for the genetic gender code.
When the eggs are being formed in the female, the chromosomes split and either the “Z” or the “W” chromosome is incorporated into the egg while the extra is either re-absorbed or expelled from the body naturally. When mating occurs, the male sperm fertilizes the egg with the only component it can possibly provide, even though the chromosomes have split. The result is either a male or female offspring with a genetic code provided from each parent animal.
Species not specifically listed in the list above are not currently known to be gender determined based on incubation temperatures.
At first, it looked like a record for reptile sperm retention. DNA samples were taken along with finally determining that the offspring was male, and the results shook the scientific world to its reptilian foundation. DNA samples from the mother and offspring looked basically identical except for a few minor coding signatures that were totally missing. Along with Dr. Smith, samples of other occurrences of the same thing were compared with quite similar results. Parthenogenesis in snakes had been confirmed!
The problem this now presented was figuring out exactly how this phenomenon happened. They had to look again at a number of offspring, a couple of which had survived and a good number that had been stillborn, and recheck the gender. It began to appear that all viable offspring had in fact been male with no complete female offspring produced.
If more information on this event, and other similar events, can be found, we will post it here as soon as possible.