Reptile Sex Determination: A continuum?

[Mendel's Balls]

Reptiles have been up to this point thought to have two mechanisms of sex determination: a genetic system based off the Z and W sex chromosomes and a environmental mechanism based off of incubation temperature (Known as temperature-sensitive determination or TSD).

Interesting experimental work published in Science this week challenged these "categories". An Australian group took the central breaded dragon, which had been previously shown to use the genetic system and incubated the hatchlings over a range of temperatures. They found that between 72 and 90F that about half appeared male and half were female. This was expected since meiosis would produce an equal amount of Z-containing and W containing ova.

The surprising result came when the researchers looked at the sex ratio of the hatchlings incubated above 93F. They found only two males out of the 35 eggs that hatched. This skewed sex ratio suggested that temperature had trumped genetics at elevated temperatures. The researchers interrogated the situation further. Using a DNA test based off the W chromosome, they showed that 17 of the 33 female hatchlings were genetically male (ZZ). In other words, they ruled out a statistical anomaly and showed that at high temperatures sexual genotypes (ZZ vs ZW) do not really determine gender (sexual phenotype).

You can read more about this work below.

http://www.livescience.com/animalwor...izard_sex.html

http://www.sciam.com/article.cfm?art...9&chanID=sa003

You can also here an interview with Alex Quinn, the main author on the paper at the Science Podcast.

http://podcasts.aaas.org/science_pod...ast_070420.mp3

The story/interview begins at 8:20 of the podcast.

The main author suggested in a 2004 BioEssay that sex wasn't solely genetic vs. TSD-- That these were instead the extremes of a spectrum. This new works seems to provide solid support for his idea.

So global climate change might not solely affect crocs and turtles, it might also affect many more reptiles than previous thought!

[Mendel's Balls]

One more link:

http://www.newscientist.com/article/...x-trigger.html

[daniel1983]

I bet the 17 'females' with male chromosomes produced by incubating at higher tempatures would show aggression toward males and don't breed well.

Similar happenings occur when incubating TSD animals like leopard geckos. "Hot females"or "Cold males" are a terms commonly used to describe males or females that are produced on the borderline temp when incubating for TSD. For example, If you incubate a clutch of leopard geckos to be male but incubate at the low end of the range for male TSD incubation....you could possibily end up with a female. When these animals are produced, they are poor breeders and can be aggressive with the opposite sex.

I don't know if any genetic studies have been done to check their chromosomes but I could guess it would be interesting and yeild similar results.

Thanks for the good read.

[Mendel's Balls]

I bet the 17 'females' with male chromosomes produced by incubating at higher tempatures would show aggression toward males and don't breed well.

Similar happenings occur when incubating TSD animals like leopard geckos. "Hot females"or "Cold males" are a terms commonly used to describe males or females that are produced on the borderline temp when incubating for TSD. For example, If you incubate a clutch of leopard geckos to be male but incubate at the low end of the range for male TSD incubation....you could possibily end up with a female. When these animals are produced, they are poor breeders and can be aggressive with the opposite sex.

I don't know if any genetic studies have been done to check their chromosomes but I could guess it would be interesting and yeild similar results.

Thanks for the good read.

Great way to incorporate your practical experience with the science Dan.

In his interview on the podcast, Dr. Quinn does indeed speculate that many reptile species have been traditionally thought as only TSD might have genetic system of sex chromosomes!

[daniel1983]

Now get me some articles on "gender determination by social grouping"......LMAO.

Always been a topic of debate amoung monitor keepers. Some people claim that a group of monitor lizards(some species) raised from hatching to adulthood will 'sort out' their sex as they develop after hatching.

Interesting stuff...

[Mendel's Balls]

Now get me some articles on "gender determination by social grouping"......LMAO.

Always been a topic of debate amoung monitor keepers. Some people claim that a group of monitor lizards(some species) raised from hatching to adulthood will 'sort out' their sex as they develop after hatching.

Interesting stuff...

Interesting stuff indeed, there are certainly more things to respond to in the environment than just temperature! I definitely will keep my eyes peeled for that!

Any idea of which species of monitor lizards have been claimed to show this phenomena?

[daniel1983]

Any idea of which species of monitor lizards have been claimed to show this phenomena?

Species that are commonly raised in groups....Varanus acanthurus sp. and other small monitors. Most people are 'so-so' on their opinions on the topic...some people believe it to be fact, others just a odd observation, and then people that think it is some bad information spread around.

For example, here is an excerpt for a caresheet by Pro-exotics when they touch on the subject
http://www.proexotics.com/care_ackie.html

For those of you wanting "a pair" of Ackies, or a "female" baby, you have to understand that monitors (of all types) are not visually sexable as babies, and there is absolutely no way to guarantee a particular sex when you are selling babies. Anyone who tells you different is trying to deceive you. Sexual characteristics start showing up as early as six months old, and as late as a year. You can look for head shapes, body shapes, hemipenal bulges, and other factors when trying to determine sex, but it is all still educated guess work. Unless a male monitor plainly everts a hemipene in your view, it is so very difficult to be sure of the sex of your animal (females will also evert a similar looking hemiclitoris, only confounding the situation). Some folks may have a "female" monitor for 3 years before it has suddenly everted a hemipene that wasn't thought to have existed in the first place.

However (and with dwarf monitors that’s a pretty BIG however), a pretty interesting and intriguing theory about the social sexing of hatchling dwarf monitors has emerged.

It is generally agreed (among the dwarf monitor breeders in the u.s.) that baby Ackies determine their gender according to social group after hatching. It is believed that one animal becomes a dominant male, and the other animals become female, basically. At this time, we have not had a customer report back to us with a male heavy group of Ackies purchased from Pro Exotics. Seeing as we group these animals immediately after hatching according to customer purchases and configurations, we have always had two Ackies be a pair, three Ackies be a trio (1.2), five Ackies be either 1.4 or 2.3, but not one instance of a heavy male group.

Some monitors are extreamly hard to sex (almost impossible) when they are young. So maybe, people have just assumed that they 'socially determine gender' because the 'gender indicators' are not present until almost adulthood.

I want to say that I have heard of research on the topic....but not to much of the findings.

Like I said, let me know if you come across anything