Sex determination in Varanids?

Rob_H · 03-27-13, 02:59 AM

Hi all, a bit of a 'History of captive Varanids' question....

Sorry if this is hugely outdated, but what happened to all the hype about Varanids having their sex determined socially? As in, if you raise a pair of juveniles up together, the dominant one always becomes the male and subordinate the female?

Does anybody know who started this rumour? I remember it seemed almost gospel around >10 years ago with ackies.

Obviously this would be pretty interesting considering the Varanids tested since then have decently differentiated sex chromosomes.

Cheers! And awesome forum by the way!

Rob

Starbuck · 03-27-13, 07:51 AM

I think that may have been a chicken vs egg scenario....
Rather than the dominant animal BECOMING male, it was that males simply WERE (or tended to be) more dominant.

[Edit]: I think varanid sex determination is chromosome dependent. The following is my reasoning as to WHY it may appear as dependent on social interactions.

This makes sense from an evolutionary standpoint for the following reason:
Male offspring cannot produce further offspring, they can only hope to mate with as many possible females to contribute their genetics in a higher proportion. Therefore, it makes sense for juvenile males to grow faster, get larger, and become 'dominant' over other males, which then increases their chances to mate, thus increasing their contribution to the next generation. Males tend to mature faster quicker, for this reason.
Females, on the other hand, benefit from a slower rate of growth because they are able to hold off on reproducing until they are larger and more well equipped. i.e. if a female lizard can reproduce at 200 grams, and she grows lets say 85 grams/year, she wont be able to reproduce until her third year, at which point she will be ~250 grams, and have 50 'extra' grams of body condition. As a female, it pays to be slow and steady early on, because your offspring have higher survival rates if the mother was in good body condition, decent size, etc.

This is mostly conjecture, as i have done only little bits of research into varanids, and hadn't heard this theory r.e. sex determination until now, but i have done a good bit of research on sex determination and offspring fitness across many members of reptilia.
I apologize if any of this information is incorrect, but this is what makes sense to me from what classes ive taken on reptile biology.

Also, I am pretty certain there is conclusive evidence of sex chromosomes in varanids, and they operate as female heterozygotes and male homozygotes, but there are quite a number of papers on this.

murrindindi · 03-27-13, 12:18 PM

Quote:

Originally Posted by Rob_H

Hi all, a bit of a 'History of captive Varanids' question....

Sorry if this is hugely outdated, but what happened to all the hype about Varanids having their sex determined socially? As in, if you raise a pair of juveniles up together, the dominant one always becomes the male and subordinate the female?

Does anybody know who started this rumour? I remember it seemed almost gospel around >10 years ago with ackies.

Obviously this would be pretty interesting considering the Varanids tested since then have decently differentiated sex chromosomes.

Cheers! And awesome forum by the way!

Rob

Hi, as far as I know it was Frank Retes, at least he`s the only person I`ve met on the forums that makes those claims?
So if we put two animals together their sex will be determined by the dominant one always being (or becoming if it was born female) male, and the subordinate one will miraculously turn into a female, even if it was born male?? I`ll stick with the SCIENTIFIC evidence....

Aanayab1 · 03-27-13, 01:31 PM

Starbuck, nailed it! At least from the small bit I know. I know of fish and plants that exhibit hermaphroditism but no reptiles. Not by far saying I know that for fact. Here is an interesting read. It is not exactly the topic at hand but does mention the chromosome topic. Also explains in sort why an individual may believe the rumor, in the part about sex ratio.

I can not create a link do to the databases restrictions but I can post the citation of the paper. The paper can be found either through JSTOR or Google scholar. A bit out dated but worth the read.

Sex Ratio and Breeding Season of Varanus acanthurus
Author(s): Dennis King and Lina Rhodes
Source: Copeia, Vol. 1982, No. 4 (Dec. 21, 1982), pp. 784-787 Published by: American Society of Ichthyologists and Herpetologists (ASIH)

jarich · 03-27-13, 01:54 PM

Ya, thats some pretty poor science to say they would just change sex. There is however, one possible explanation that could have caused the misunderstanding. Varanids have displayed parthenogenesis on a number of occasions. This means that an egg laying female can actually have fertile eggs without ever coming into contact with a male. Its rare, but does happen. So while it wouldnt be that the monitor changed sex, they can apparently 'clone' themselves, in essence, without the need for the opposite sex.

Aanayab1 · 03-27-13, 02:27 PM

I have read something on that as well jarich, although in the case I read about it was determined that the specimen was a hermaphrodite. As in the abnormal mutation, not the natural mutation found in fish, insects and plants. This all being in the chance we are both thinking of the same instance. I will do my best to find the read. I was under the impression that parthenogenesis was mainly found in insects, plants and some arthropods? But when found to take place in inverts, hermaphroditism was the case. I would enjoy to read any information pertaining to the commonality of parthenogenesis among varanidae.

murrindindi · 03-27-13, 02:33 PM

Quote:

Originally Posted by jarich

Ya, thats some pretty poor science to say they would just change sex. There is however, one possible explanation that could have caused the misunderstanding. Varanids have displayed parthenogenesis on a number of occasions. This means that an egg laying female can actually have fertile eggs without ever coming into contact with a male. Its rare, but does happen. So while it wouldnt be that the monitor changed sex, they can apparently 'clone' themselves, in essence, without the need for the opposite sex.

Hi Josh, there was no misunderstanding with what Frank R. describes happens (nothing to do with parthenogenesis), he most definitely claimed they actually changed sex if they were kept in groups and one was dominant. In other words, when they hatched they were neither male nor female, and "decided" to develop into male or female some time later!? I have seen him claim that a several occasions. I think I would rather believe in little green men from Mars....

Parthenogenesis may not be all that rare in wild Varanids.

murrindindi · 03-27-13, 02:38 PM

Quote:

Originally Posted by Aanayab1

I would enjoy to read any information pertaining to the commonality of parthenogenesis among varanidae.

Hi, I don`t have links, but type into your search engine "parthenogenetic Varanids", there are several published papers. It`s happened with V. komodoensis (twice), V. ornatus, V. panoptes (and perhaps more that weren`t recorded).

jarich · 03-27-13, 02:44 PM

Quote:

Originally Posted by murrindindi

Hi Josh, there was no misunderstanding with what Frank R. describes happens (nothing to do with parthenogenesis), he most definitely claimed they actually changed sex if they were kept in groups and one was dominant. In other words, when they hatched they were neither male nor female, and "decided" to develop into male or female some time later!? I have seen him claim that a several occasions. I think I would rather believe in little green men from Mars....

Parthenogenesis may not be all that rare in wild Varanids.

Ya, that sounds about right! Thought Id give it the benefit of the doubt, but he makes that hard sometimes.

Anyway, here is the article I was thinking of:

http://www.varanidae.org/Vol4_No1_Hennessy.pdf

Though like Stefan said, I am sure there are many more.

Rob_H · 03-27-13, 03:13 PM

Thanks Murrindindi (good to see you here by the way!), and everyone else. I just searched on another forum and found that Retes used to claim this.

I agree it's extremely unlikely since no other reptile has shown it, it was more out of interest how the idea came about. If anyone's interested there ARE actually vertebrate examples of socially-induced sex changes. Clownfish and blue headed wrasse are some, where sex depends on the relative hierarchy in a social group. If the dominant animal carks it, the next most dominant changes its sex to take over (in clowns this is a female, vice versa in wrasse). Pretty cool system.

Of course ackies certainly don't change sex as adults, so for this to be adaptive in the juvenile stage then juveniles of the same age would have to live in stable social groups whilst growing up. Also doubtful.

smy_749 · 03-27-13, 03:19 PM

I don't have time to read all the posts, because I'm starving and there is 3 sandwhichs infront of me, so I don't know if anyone mentioned this. But I know there is a species of salt water wrasse fish that the male has a harem of females. When the male dies for any reason, only ONE of the females changes gender and becomes the new male. The deciding factor for which female will turn into male is unknown I believe, but thought to have something to do with the most dominant female among the group. So theoretically if you believe that male ackies in the wild had the same sort of harem system, its not far fetched. And I know that FR believes that ackies are social in the wild from what crocdoc has stated, so I see where hes coming from. But yea....no, I don't think it happens.

Aanayab1 · 03-27-13, 09:46 PM

My mind is officially if overload... I read three papers and I'm going back for more after this haha. I love learning this type information,its what I live for.

I truly thank you murrindindi and jarich for bringing this subject to light for me.

crocdoc · 03-27-13, 11:32 PM

There's another reason for the belief that raising monitors together will produce an even number of males and females. It's called statistics. As the number of males and females hatching is roughly even, if you raise two at a time over and over again, on average you will get a high number of 1:1 pairs. Magic!

I'll explain it using coins. If you flip a coin, you have a 50% chance of it landing heads and a 50% chance of it landing tails. If you flip two coins at once, there's a 50% chance of coin 'A' landing heads and a 50% chance of coin 'B' landing tails, so the combined probability is 25%.

There's also a 25% chance of coin 'A' landing tails at the same time coin 'B' lands tails.

And a 25% chance of coin 'A' and coin 'B' both landing heads.

But (and here's the tricky bit), there's also a 25% chance of coin 'A' landing tails and coin 'B' landing heads, giving us another head/tail combo, but different than the first one. In other words, there's two ways we can get a head/tail combo (with either A or B being tails and the other being heads), so the combined probability becomes 50%. Twice as much as either two heads or two tails.

Combine a 50% chance of something occurring with the human tendency to remember patterns and for memory to be easily skewed or influenced, so that we remember the favourable outcomes but quickly forget those that don't fit in with our preconceived ideas and... voila, we have a new theory of monitor social sex changes.

It's a small wonder some people are anti-science, as it'll often spoil a good story with the truth.

By the way, the person that came up with the idea of the monitor social sex changes also happens to think that wild monitor babies bond in the nest, hang out together socially for life and then pair up (even though they are siblings) when they hit reproductive age. Consequently the social sex change was seen as part of a much larger picture. We had many a heated conversation about this (for I think it is hokum).

As for parthenogenic monitors, they aren't hermaphrodites. It's lone females producing male babies.

infernalis · 03-27-13, 11:37 PM

Quote:

Originally Posted by crocdoc

It's a small wonder some people are anti-science, as it'll often spoil a good story with the truth. .

Two thumbs up.

smy_749 · 03-28-13, 06:30 AM

Good point with the statistics. If he had done this with 3 or 4 juvies, and consistently only received one male, and under the same incubation controls, raised another group of babies, each alone in isolation, and received the expected 50/50 ratio, then maybe you could look into it.

This is the kind of thing where learning true science, and the proper technique for experimentation comes in handy. Otherwise evidence and coincidence start to form an intimate relationship and you lose all sense of reality. *Checks totem*

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