Temperature-dependant sex determination in Tokay Geckos. Any evidence for or against?

[tombo46]

It has mostly been said that TSD is not possible in Tokay Geckos however I have never actually seen any evidence for or against. As most Tokays are left in situ there isn't much evidence to suggest otherwise. That being said I have heard of several people selling Tokays as "should be female/male as they were incubated at X/Y/Z temperature". This is either the babbling of someone who hasn't got a clue, or someone who maybe knows more than we do through personal experience? Either way I feel it's wise not to ignore it until I find some evidence suggesting otherwise.

If I can't find anything to prove either argument I would like to give it a crack myself. I am pairing up around 30 pairs this year so aside from eggs from very crucial pairings that must survive incubation I will have some eggs going "spare" as it were. I would like to try and externally incubate them to see if I can get some sort of bias when it comes to animals incubated at different temperatures. It will also hopefully give us more insight in to the ridiculous incubation times with tokays!

While this little experiment will be far from scientific I hope it may be able to shed some light.

Obviously there are various hurdles to pass in making this happen. Firstly, removing the eggs! I have seen many people show Tokay eggs incubating externally and I'd love to know how it happens!

At what point do Tokay embryo's attach themselves to the wall of the egg? When does it become to dangerous to turn them?

What temperatures to incubate them at?

As for us Tokay morph breeders it may be useful for our breeding projects to be able to determine sexes.

There's a tonne of other things to think about too but for the time being they escape me.

So has anyone got any evidence for or against TSD in Tokays? If so please share, whether it be personal experience or actual study. If nothing can be found then answers to the above questions would be helpful!

 

[Ingo]

Let me quote Tony Gambles 2010 review:

"The genus Gekko is perhaps one of the most interesting gekkotan genera with regard to sex determining mechanisms. Many species have been karyotyped and 3 species, G. gecko, G. japonicus and G. hokouensis, possess heteromorphic sex chromosomes [Yoshida and Itoh, 1974; Solleder and Schmid, 1984; Kawai et al., 2009]. Gekko gecko has an XY sex determining mechanism [Solleder and Schmid, 1984] although this species had been karyotyped several times before with no observed heteromorphic sex chromosomes [Cohen et al., 1967; De Smet, 1981; Wu and Zhao, 1984]. The failure to observe heteromorphic sex chromosomes in the previous studies is certainly related to the banding techniques used by Solleder and Schmid [1984] but could also be due to the presence of cryptic, undescribed species. While there has yet to be a comprehensive review of G. gecko across its range, preliminary evidence suggests several cryptic lineages within G. gecko [Qin et al., 2007]. The largely equal amounts of heterochromatin observed on the X and Y chromosomes led Solleder and Schmid [1984] to suggest that the sex chromosomes of G. gecko were at an early stage of differentiation. This seems very plausible when examined in a phylogenetic context (fig. ​(fig.3)3) although data from additional species of Gekko are clearly needed to confirm this. Interestingly, the Y chromosome of G. gecko was larger than the X chromosome, a condition also found in G. japonicus [Yoshida and Itoh, 1974]."

Having quoted that, I still have to say, that for my tokays I do definitely see more male hatchlings in summer and more females in fall. Embryo letality does not interfere with this observation, since hatching rate is 100%.
For some other species of the genus TDSD definitely is relevant.

P.S.: It is easy to collect tokay eggs: Just cover the favourite egg laying places with some appropriately coloured paper or thin cardboard. Egg attached to this can be easily removed together with that substrate.

Best regards

Ingo

 

[Riverside Reptiles]

Great info Ingo. Thanks

 

[billewicz]

OK, I'd love to have a magic answer to Temperature-Dependant Sex Determination as would anyone who has had to find the space and separate enclosures to raise up lots of hatchling for several months.

And yes, I'm curious about this claim. Obviously it could be very easy to make this claim just to avoid the time and expense. The new owner would be 6 to 10 months down the road before they would really know.

So far, visual indicators are not reliable regardless of some web sites show 'definitive' photos and just a couple of weeks. You can 'pop' them for hemipenes but the possibility of a dropped tail in young Tokay is quite high.


Since I allow most of my eggs to incubate in the enclosure, I get very mixed results. I can have 50/50 in one enclosure next to one that produced all females and heavy males in the next. These are all in the same room. If I thought for a minute temps would determine sex, I'd work to augment conditions to produce a more predictable outcome.

This would help in keeping breeding lines and morph pairs more efficiently stocked. And if it were accurate enough to comfortable sell juveniles at 15 grams like they do Leopard Gecko, one could actually break even or even produce a profit in breeding Tokay.

Because most buyers want a sexed animal, the breeders is in a position of holding the juvenile for about 6- 8 months in expensive enclosures. Not shoe box racks. This is the single biggest profit-killer in Tokay breeding.

Highly accurate TDSD would bring a lot more breeders into Tokay which would help shorten the time needed to prove out all the cool genetics that are only available as wild caught animals.