And Also...

[Bindi]

Does anybody know at what stage of incubation a torts sex is determined? I did read it somewhere - at roughly day so and so but can't remember at what stage or where I read it

[egyptiandan64]

It's the middle third of incubation, so between day 23 and 47.

Danny

[Bindi]

Cheers Dan xx

[Kirkie]

I thought it was earlier than that. After day 7 but before day 29 for Testudo Hermanni Boettgeri.

Some experiments were undertaken where a "male" temperature of 30C was used throughout but increased for as little as 7 days between *days 7-28 and females would result. If the temperature increase was undertaken before day 7 or after day 28, it resulted in males, indicating that the fix of the sex was taking place days 7-28.

http://www.schildpadden.akkido.com/docs/pub2.pdf

I did a split temperature incubaton on a Boettgeri which hatched last week. 28 days at 32.5-33C then dropped to 30 for the remainder. Hatched on 55 days. Should know in a year or so if it's a female.

[Bindi]

I know exactly when it will happen - day 19 - when my leccy is going to be switched off

[egyptiandan64]

But they did the exact opposite experiment where they were keeping the eggs at 32C and than dropping the temperature to 29C bteween days 16 and 24 and still got females. You would think if the time for changing or influencing sex was between 7 and 27 days that that drop would produce males. Wonder why it didn't.

Danny

[Kirkie]

In figure 10b on that link, they haven't followed their own ground rules in the 32.5 down to 30 test that produced females. They started the lower temp at day 16 to day 24 and day 33-40 which was outside of the scope of the reversed experiment. In fact it reads as if this was only attempted twice.

If days 25-28 are the key days, they would get females based on what they did. I'd assume that longer exposure to lower temperatures are needed to fix males as the whole development process is slower at lower.

[egyptiandan64]

I did read that after, that they figured you'd need a longer time at the lower temperature to get males by dropping the temperature.
Than they go on to say that there may be a male bias in the sex ratios as more tortoises die the higher the temperatures get (and if you go to low also). I would have thought if a tortoise went full term, but didn't hatch that they would be able to disect it and figure out what sex it is. They didn't mention that they did in the study. If they had it might have made for a more accurate sex ratio at different temperatures.

Danny

[Kirkie]

Good point Dan. It is all based on survivorship. I'm incubating my one good TH Hermanni egg at 29-30c to be on the safe side (and I want a male for my two little females).