Incubation determining sex

[W.T.BUY]

Hey all just thought this great link. http://notexactlyrocketscience.word...perature-control-the-gender-of-jacky-dragons/


mong Jacky dragons, females are both hot and cool, while males are merely luke-warm. For this small Australian lizard, sex is a question of temperature. If its eggs are incubated at low temperatures (23-26ºC) or high ones (30-33ºC), they all hatch as females; anywhere in the idle, and both sexes are born.

This strategy - known as ‘temperature-dependent sex determination (TSD) - seems unusual to us, with our neat gender-assigning X and Y chromosomes, but it’s a fairly common one for reptiles. Crocodiles are all-male at high temperatures and all-female at low ones, while turtles flip the rules around and produce more males in cooler climes. Now, a thirty-year old idea to explain this puzzling system has finally been confirmed.
Assigning gender based on temperature is not uncommon but it is nonetheless puzzling. Gender seems like an incredibly fundamental physical trait to leave to something as variable as the temperature of your surroundings. How has such a system evolved? What possible benefits could a species receive by switching control of from chromosomes to the environment?
Testing the theory
The question is not lacking in possible answers. The most widely accepted hypothesis was put forward by Eric Charnov and James Bull over thirty years ago. They suggested that TSD occurs when the temperature of the environment affects the success of males and females strongly but differently. Parents can then use local temperatures as a sort of crystal ball, producing more males in conditions that are suited to males, and more females in conditions where they have the edge.
The idea is sound, but testing it has been remarkably difficult. The ideal experiment would involve hatching both males and females at the entire range of incubation temperatures and compare their success over the course of their lives. Obviously, the very nature of TSD rules out that approach; how do you hatch males at low temperatures if those same conditions, by definition, beget females?
If that weren’t enough, most species that use TSD are large and long-lived. Imagine following a turtle for its entire 60 year lifespan and you begin to see the problem. All that changed this decade when TSD was found in the small and short-lived Jacky dragon (Amphibolorus muricatus). With a lifespan of 3-4 years, here was an animal that could be reasonably studied in experimental conditions.
With one problem down, Daniel Warner and Rick Shine from the University of Sydney solved the other by using hormonal treatments to sunder the link between temperature and sex. Temperature may decide gender but it does so through hormones. The key event is the conversion of testosterone to oestradiol (a relation of oestrogen) by an enzyme called aromatase. This happens at low temperatures and tells developing dragons to become females.

Warner and Shine overrode this process with a chemical that blocks aromatase. With the enzyme disabled, the duo managed to hatch male babies at temperatures that are exclusively female. The hormonally nudged Jackies were physically similar to their male siblings who developed in the normal way; that was essential if they were going to be compared fairly. The duo raised the babies in enclosures that mimicked their natural environments, and waited.
Fine-tuned sex
After three consecutive breeding seasons, Warner and Shine found (as predicted) that males sired more offspring on average if they were hatched at an intermediate 27ºC, a normal temperature for them in natural conditions. Males hatched at temperatures that are usually the province of females produced almost three times fewer young. The reverse was true for females; they enjoyed greater reproductive triumphs if they were hatched at a cooler 23ºC or a warmer 33ºC.
Although these results don’t explain why males and females should fare better at different incubation temperatures, they do fully vindicate the Charnov-Bull model. Exactly as predicted, male Jacky dragons produce more young if they hatch at temperatures that usually produce males, and likewise for females.
Such careful fine-tuning has done the lizards well over the course of evolution but it may put them in danger as the globe continues to warm. Like crocodiles, turtles and other reptiles that use TSD, the Jacky dragon may become a casualty of climate change, as rising temperatures lead to an all-female population and no way of producing a new generation.
Find out more: I’ve blogged previously about thebearded dragon uses both sex chromosomes and TSD to determine gender. At higher temperatures, males ignore their genes and become females instead.

 

[W.T.BUY]

When the heat is on, male dragons become females

Posted on 1 May, 2007 by Ed Yong

It seems almost fashionable now to blame everything on climate change, but the most unusual claim yet is that it could lead to sex-changing lizards.​

For humans and other mammals, sex is neatly determined by the X and Y chromosomes. If you have a Y you are male, and without it you are female. Reptiles however, use a variety of strategies, and the mammalian X/Y system is just one of them.
In some species, the female is the one with different chromosomes, in this case Z and W, and the male has two Zs. And some reptiles ignore sex chromosomes altogether. For them, an individual’s sex is determined by the temperature that their eggs were incubated at.
Scientists had long believed that these strategies were mutually exclusive with each species choosing one of the other.
But Alexander Quinn and colleagues form the University of Canberra have found that an Australian lizard, the central bearded dragon (Pogona vitticeps) flouts this rule. It has become the first animal known to use two separate methods to determine the sex of individuals.

The dragon uses the Z/W system, where the males carry two Z chromosomes and the females have a Z and a W. But Quinn found that these genes are only the dominant influence on gender if eggs are incubated between 20 and 32 degrees Celsius.
At higher temperatures, males ignore their genetic heritage and become females instead. When Quinn incubated broods of eggs between 34 and 37 degrees Celsius, the hatchlings were almost invariably female. And as predicted, about half of these sisters were genetically male. For dragons at least, when the heat is on, the men turn into women
Quinn believes that the key to the manliness of boy dragons lies in a temperature-sensitive protein produced by the Z chromosome. The protein’s activity needs to surpass a certain threshold before a dragon can become male. For that, there need to be two copies of Z, and the temperature must be just right.

Reptiles that use temperature to assign gender must have fine-tuned their systems over time to cope with an ever-changing environment. But Quinn fears that the current pace of climate change may be too rapid for these animals to adapt to.

If temperatures rise far enough to bias an entire species over to a single gender, extinction would be all but inevitable. These warnings have been sounded before, and Quinn’s work suggests that they should be shouted a little bit louder.




Another great read.

 

[W.T.BUY]

Male lizards of a species known as southern water skinks, which live high in the mountains of southeastern Australia, better hope the threat of global warming is a farce. If Earth does warm up, they may find themselves left with no females to mate with, and the species pushed to extinction. The concern arises because scientists have found that females of the lizard species Eulamprus tympanum control the sex of offspring by controlling their own adult body temperature.

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This is the first time that temperature-dependent sex determination has been reported in a species that gives birth to live young, according to the researchers who described their findings in the August 16 issue of Nature.
Preliminary data indicate that when temperatures are warm, the female lizards give birth exclusively to males. That doesn't bode well for the future of the species if global warming models are correct, said Kylie Robert of the University of Sydney, a co-author of the report.
"This species is already restricted to mountain tops," she said. "With a 4-degree Celsius [7.2-degree Fahrenheit] rise as predicted by global warming models, they cannot retreat to cooler regions and will, in turn, produce entirely male offspring and eventually become extinct."
Unusual Trait Among Reptiles
The sex of an advanced organism is determined through a well-orchestrated cascade of biological events. The reproductive organs begin undifferentiated, then follow a pre-programmed pattern of development to become either female or male.
In vertebrates, sex is determined by genetics at the time of fertilization, as in humans, or by environmental factors, such as temperature, that occur after fertilization.
Temperature-dependent sex is common among many egg-laying reptiles, such as crocodiles and turtles. In a nest, incubation temperatures can vary widely. Eggs at the top of a nest, for example, incubate at different temperatures than eggs in the middle or at the bottom, Robert explained.
Finding the same kind of trait in a species that gives birth to live young, such as E. tympanum, is surprising. Reptiles keep their body temperature relatively constant.
"It is the first demonstration in a live-bearing reptile," said David Crews, a biologist at the University of Texas in Austin. "It goes against one of the basic assumptions about [temperature-dependent sex determination]—that it occurs in egg-laying reptiles."



more.....


Will this change the way YOU incubate eggs?

 

[Bushfire]

Peter Harlow did a talk about this at a VHS meeting some years ago. Some of the species he talked about which I remeber were frillies, water dragons, jackies, southern forest dragons, and I think a few rock dragons. He also had a list of dragons that didnt use TSD. Ive found that the majority of keepers don't use this information when incubating their eggs, which is a shame and from the buyer POV can make it harder to buy a particular sex ie. female frilled dragons. Back when I kept dragons I always split the clutch into two and incubate them separately at different temps.

 

[W.T.BUY]

Peter Harlow did a talk about this at a VHS meeting some years ago. Some of the species he talked about which I remeber were frillies, water dragons, jackies, southern forest dragons, and I think a few rock dragons. He also had a list of dragons that didnt use TSD. Ive found that the majority of keepers don't use this information when incubating their eggs, which is a shame and from the buyer POV can make it harder to buy a particular sex ie. female frilled dragons. Back when I kept dragons I always split the clutch into two and incubate them separately at different temps.

Hi mate was just wondering if you remember if the Ctenophorus and Diporiphora used TSD. Would love to know thx.I would have loved to hear that talk.

 

[W.T.BUY]

Bump i've googled and found that most rock dragons Are TSD does anyone know if tommy round head dragons are TSD???

 

[Kirby]

it doesn't turn them magically into females like a light switch, it makes them hermaphrodites. there DNA tells them they should have been male, but they are born with the sexual organs and body of a female. correct me if im wrong, i read the articles when they were published a while back.

i think i would rather a normal, 50/50 clutch at normal temps then fiddle around with the determined sex.

 

[Bushfire]

It doesn't make hermaphrodites but you are right in that in some but not all, DNA may be telling it to be another sex, although it gets ignored. I played abit with EWDs temps and that those in the clutch incubated at the desire temp to be females went on to produce normal clutches themselves.

With those species that use this strategy, we really are fiddling around anyway, as the majority of us incubate our eggs at constant temps as opposed to the wide variety of temps a natural nest may experience, in which case the gravid female has an influence. Ive found with frill necks, the temp that the majority of keepers incubate their eggs at will give them a majority of males.

 

[W.T.BUY]

How Hot is too hot for a dragon egg?

 

[Kirby]

Bushfire, i know that these 'females' who technically there DNA could have told them to be male can and will produce viable clutches.

where do you draw the line. if snakes and reptiles should be natural, no hybrids etc. why not there sex aswell.

it depends u guess.

W.T.BUY 32C i beleive is tops for beardies. at this temp they will likely be female. BUT having said that, spikes up to 36 have been known to kill the fetus, but in some creates some odd and exciting morphs. but, why would you purposely risk killing a whole clutch or two, risking deformities at the same time.

 

[W.T.BUY]

Bushfire, i know that these 'females' who technically there DNA could have told them to be male can and will produce viable clutches.

where do you draw the line. if snakes and reptiles should be natural, no hybrids etc. why not there sex aswell.

it depends u guess.

W.T.BUY 32C i beleive is tops for beardies. at this temp they will likely be female. BUT having said that, spikes up to 36 have been known to kill the fetus, but in some creates some odd and exciting morphs. but, why would you purposely risk killing a whole clutch or two, risking deformities at the same time.

TSD is natural and so is ïntergrading"In the wild. Surly during great temp cycles eg "la nina" 'El nino" you would get pure male and pure female clutches. TSD is normal its not something that humans have grafted in reptile DNA:lol::lol:

 

[Bushfire]

where do you draw the line. if snakes and reptiles should be natural, no hybrids etc. why not there sex.

I think you misread the article you got your information from. TDS is a very natural process and most definitely happens out in the wild. From what I have read TDS doesn't work in pythons, unknown in monitors (probably not), SOME dragon species, many turtle species, and of course crocs. In the wild those dragons that use TDS the female would sort out a suitable location for her eggs, she may or may not be selecting to get a certain sex ratio its really difficult to tell as the weather and nest conditions would change too much over the the incubation to understand if she has that foresight. There is no temp out there that allows the DNA to determine the sex in TDS species from my understanding. For example in EWDs like everything else there is a range of temps that will result in hatchlings. In EWDs the lower temps in the hatchable range of temps in most cases produce near 100% female; at the higher end of the hatchable range again near 100% females but deformities are very possible if you incubate close to the extremes in that range. In that mid range, ie. 27 -29oC you will get varying percentages of males peaking at 80% at 28oC. In some species that would mean some DNA females become males. I wouldn't be making the mistake if you incubate within this mid range to conclude that DNA tells it what sex it is because you are getting percentages of both sexes.

Bearded dragons do use TDS as well, but its different in that to get that near 100% female range, both upper and lower ranges, you are also within the lethal and deformed ranges so yes technically it can be done in Beardies but realistically not worth it (No use having an all or near all female clutch if that means they are all dead).