# Incubation temp and sex



## Reptilony (Sep 2, 2018)

So I found this article that shows that temperature absolutly 100% determine sex. Does any breeder knows if this is true by experience? I would like your opinions.


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## wellington (Sep 2, 2018)

Not true. The higher temp has a better chance of giving females. However, it is no way near 100%.


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## 2turtletom (Sep 2, 2018)

I would say that this is the result of a limited data set. This graph presents their results that one clutch of eggs incubated at 32.5 C resulted in 0% males. This is just the result of one experiment. Your results may, and will, vary.


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## Reptilony (Sep 2, 2018)

Ok thanks a lot. Now I know my sully is not 100% a female and my breeder is 100% wrong.


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## wellington (Sep 2, 2018)

2turtletom said:


> I would say that this is the result of a limited data set. This graph presents their results that one clutch of eggs incubated at 32.5 C resulted in 0% males. This is just the result of one experiment. Your results may, and will, vary.


I don't see anything or am I missing it, about at what age did they determine the sex of the tortoises? They all look female until they are older, 3 plus years.


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## wccmog10 (Sep 3, 2018)

Temperature depended sex determination is a well documented phenomenon. Crocodilians, lizards and turtles show some level of TSD. Depending on what group you are looking at- low incubation temperatures may produce males or females. In some cases you can have females produced at low and high temperatures and males produced at intermediate temperatures. While these temperatures alter the statistical chance of producing male or female- it is entirely possible to produce a clutch of all males or all females. I have seen it done. Nowhere do I see in the original post how many cluctches of sulcata eggs were used. Ideally you would need multiple clutches that get mixed together and split into different incubation temperatures- to control for the variation between females. Because it is possible for some females to run a higher pivotal (the temp where you get 50:50 m/f ratio) temperature than others. It is also possible to have variation in pivotal temperatures among populations of the same species. A breeder that claims to sell a hatchling as definitely male or definitely female based on incubation temperature should have tested this his/herself by using laparoscopically sexing or raising babies to a sufficient age to determine sex. I myself do not give a 100% garuntee. I say what I tried to incubate for, what temp I incubated at and let the buyer determine. 

Interestingly- TSD still seems to produce a 50:50 sex ratio in the wild. So the pivotal temperature (in the species I know about, gopher tortoise and desert tortoise) is roughly the average wild nest incubation temperature. The pivotal temperature of desert tortoises (this information is from before the split into two species) is higher, about 31.5 C, than a gopher tortoise, about 30 C (if I remember my numbers correctly). Desert tortoises live in an environment with higher temperatures than gopher tortoises- which to me is very interesting. I also have expierence with some turtle species from temperate areas that are fairly cold, we incubated their eggs as low as 74 F. 

At the zoo we would regularly incubate for a specific sex depending on what the captive population sex ratio was.


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## Tom (Sep 3, 2018)

It absolutely is true and is 100% reliable… With SULCATAS and only when temps are strictly and accurately controlled by lab grade equipment.

This study was done with eggs provided by Mr. Richard Fife, and because of his generosity and that of the scientists who did the study, we know know which temps produce which sex in sulcatas and sulcatas only. Here is the problem in the real world: Few people have or can maintain lab grade accuracy with their temps for the entire 90+ day incubation period. If done right, the correct temp will guarantee sulcata baby sexes. It is very difficult to do it right in any typical home incubator system. Still, if the person doing the incubating is pretty close most of the time, then the temperature sex determination will also be pretty close most of the time. So in a lab with precise known temps, yes, it is 100% accurate. In my incubator here at my house, I would guess it somewhere around 75-90% accurate given the temp fluctuations that are possible.

Here is the other problem: This does NOT apply to ANY other species. No other species has been studied and documented this way. Some breeders have tracked the sexes of their babies of other species over many years and they have a pretty good idea, but other species, like Geochelone platynota, are completely unknown. Breeders "incubate for female" and frequently end up with all males, or a 50/50 mix.

So in the real world if you are buying a leopard, star, russian or greek and the breeder says it was "incubated for female", or male, you have a 50/50 shot at getting what you wanted, and maybe a little better odds with a long term experienced breeder who knows his/her individual species and has a long proven track record. If you buy a sulcata baby that was incubated under very precise and completely controlled conditions and the temperature really was what the breeder thinks it was for the entire duration of incubation, then yes, you can be sure of what you are getting.


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## Yvonne G (Sep 3, 2018)

Tom said:


> Breeders "incubate for female" and frequently end up with all males, .



I can attest to that.

I always set my incubators on the high side and so far most of my babies (YF, Manouria) have ended up male. I'm hesitant to set the temperature any higher due to the chance of getting deformed babies.


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## Markw84 (Sep 3, 2018)

TDSD is indeed well documented. However, the exact pivot points for different species have not been determined. As noted a few times above, it will vary by species and for most has not been determined. The best studies have been done with sulcatas as far as tortoises are concerned and the above study is one of the best examples. In many of the scientific experiment that have been done ( much more with aquatic turtles) the hatchlings are sacrificed and surgically sexed. That is not going to be done with rarer tortoises and endoscopy or surgically sexing without sacrificing the hatchling is expensive and tedious. How many breeders keep accurate enough records and have the accurate equipment to really monitor exact incubation temperatures AND - then allow the tortoise to grow to a reliable sexable size?

However... as @Tom notes, the accuracy of the equipment is very problematic for most. Since a single degree will greatly effect results, very few have equipment or a setup that can be controlled and even give readings that accurate. This is compounded by the issue that we don't know exactly when the sex of the embryo is "set". It appears to be in the 2nd third of the incubation period. BUT, is this a certain point where it is the temperature that day, or the accumulation of "temperature hours" over a certain point that needs to be realized over a week or two weeks??? It seems the production of a hormone called Aromatase in the embryo during this phase converts androgen to estrogen, which then leads to development of ovaries. Lower temperature inhibits the production of aromatase. So my best guess is that this is an accumulative effect over at least a week to get enough estrogen production. Will a high spike of an extra 5 degrees one or two days do it? OR will it instead need to be at least 5 days - or 10 or 20 days - of at least midday temps that bump up an extra two degrees?? We don't know this yet. So to really determine all this - very good temperature control in a very controlled incubator with a temperature logger that measures temps at exact times and intervals would be necessary. Simply watching an incubator to see that the temperature stays real close to 88°F is not good enough. However, if the thermometer happens to be accurate, and the room in which the incubator is maintained keeps the incubator stable at this temperature throughout the incubation period, at least with sulcatas, we have a pretty good chance of getting a desired result. But again, we may have a breeder that may well have a "fairly stable temp" in the incubator. But is this over the entire period? Is there particular attention to day 30 to day 50 when even a slight variation could have the most significant effect?

IN the wild the temperature in the nest chamber will be different top to bottom for the larger clutch species. That will help produce a mix. Nest selection sites also greatly effect nest temperatures. Some females seem to prefer a partially shaded area while another of the same species tends to lay in a more open area. One should yield more females than the other. An unusual hot or cold spell midway through peak incubation periods in the wild can also cause years to produce a very skewed male/female ratio. An extremely long productive lifespan is a survival mechanism to help counter this.


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## wccmog10 (Sep 3, 2018)

Tom is correct- you have to have an incubator that holds temperature very precisely. Most hobbiests do not have these high end incubators or monitor them like a researcher would. They are really expensive. He is also correct that what has been described here for sulcatas does not transfer over to other species- or other individuals of the same species from a different local. And on that note- most of us do not know what region our individuals came from. There are several species and/or populations of species that the pivotal temperature has been described for, you just need to look for scientific papers on the subject.


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