TSD, does it exist in Geoemyda spengeri?

Recently I saw a post in any online group about whether or not Geoemyda spengleri used temperature sex determination in their eggs and if lowering the incubation temperature would increase the likelihood of a male hatchling.  Here is the response that I posted:

“I’m not sure if lowering the incubation temp will help.  I don’t think G. spengleri have TSD and it would be really hard to test.  If low temperatures produced males we would see a lot of CB males because many keepers use “room temperature” to incubate their eggs.  In order to prove TSD the temperatures must remain constant throughout incubation.  To test the lower temperature scale the breeder would need a room temperature that is quite low to keep a stable temperature in the low 70′s inside the incubator.  If the room temperature is too close to the desired incubator temperature it will have an increased ability to affect the incubator’s temperature or raise above the desired incubator temperature.  That would ruin the consistency needed for TSD studies.  I incubate in a basement and I am able to keep consistent temps at 79F without any fluctuation and I would imagine I could go down to about 75F.  Any lower and the room temperature fluctuations could spike above my incubator temp.  G. spengleri have a very low tolerance for incubation temperature fluctuation in either direction.  If you incubate over 80F the hatch rate decreases considerably.  With such a small variation in safe incubation temperatures for this species I would imagine that TSD would not function as it would in a species that can tolerate a wide range of temps.  Usually a species will have several layers of TSD.  A low temp produces one sex, the midline produces mixed sex, and the high temps produce the opposite sex.  In a species that has so few degrees to play with it seems improbable to me in G. spengleri.  You never know with nature however and it is worth looking into.  Now that I have an incubator that remains constant I can test several different temperatures to see if it produces anything consistent as far as TSD goes.  It will take some time to raise up babies and I usually sell a few so I would rely on the person purchasing them to relay the sex to me.  Time will tell and it will take a lot of time!”

UPDATE: Someone suggested that TSD could be studied by the following method: “However, I don’t agree that the temperature has to be a single degree point or extremely tight confines to develop a valid research design. Something like “low” (63-68), “medium” (68-73), and “high” (73-78) should be reasonable. Some folks might like to add the “super high” temperature range (for this species) that swings into the 80s. Anyway, that’s just my thought, if someone wants to set up a study.”

My response: “The problem with using “low, medium, and high” in temperature studies is that you are deciding what constitutes the definition of low, medium, and high. You could say the low realm reaches 68F at the high end but it could be the low realm for midline “mixed sex.” That would throw off the results, or at least the interpretation of those results.  Also, how long was the egg exposed to the lower realm of “low” compared to the higher end? Maybe I’m being too strict but I feel for true temperature studies you need to focus on individual results from a single temperature at a time. Like I said, it would require a very cool room to study the lower temps without problems as most incubators heat without cooling. If a room exceeds the target temp it wouldn’t work. Even if I was fortunate to have an incubator that cooled as well as heated I think the accuracy might not be as good as an incubator that is proportional and simply heats in a cool room.  I agree, the cooler the eggs the longer the incubation and it exposes the eggs to potential problems for a longer period. The last few seasons I’ve had a 100% hatch rate. The turtles aren’t doing anything different, it’s their human that finally got his act together.”

I feel if individual temperatures are studied the results can be interpreted more successfully rather than deciding what constitutes low, middle, and high beforehand.  It could be there is no high or low and that the safe temperatures all produce mixed sex.  It will be interesting to discover what the results are and it will take a very long time with a species that generally produces two eggs per season!  This year I am going to try and test one or two temperatures with my eggs.

Please post and share your thoughts and comments about TSD in Geoemyda spengleri!


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