Sex determination in Varanids?

[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Sorry if this is hugely outdated, but what happened to all the hype about Varanids having their sex determined socially?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

[Starbuck]

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]

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.... :yes:

[Aanayab1]

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]

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]

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]

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.... :no:
Parthenogenesis may not be all that rare in wild Varanids.

[murrindindi]

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]

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.... :no:
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]

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]

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]

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]

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]

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]

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*

Final minute of Inception - YouTube (http://www.youtube.com/watch?v=L9Qp5osoH8s)

[crocdoc]

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.
You'd have to do this x several hundred times for it to be statistically significant.

There are a lot of really interesting books (Irrationality, The Invisible Gorilla etc) on perception, memory and the distortion of reality that are worth reading. We remember coincidences because they surprise us, but end up reading a lot more into them than we should. We remember the time we walked down to the shop at just the right time to bump into an old friend we hadn't seen in years, but forget the other 364 times we walked down there that year without bumping into anyone at all.

The general public has a particularly poor understanding of the statistics of averages nor what 'random' really means. For example, if the average number of fatal shark attacks in a particular year is around 1 and suddenly there's a year during which 4 people get killed, everyone (including the media) immediately assumes that sharks are increasing in number at a rapid rate. No one stops to think that sharks can't grow to man-eater size in a single year, quickly enough to bolster the number of man-eaters by 400% from one year to the next.

[infernalis]

The general public has a particularly poor understanding of the statistics of averages nor what 'random' really means. For example, if the average number of fatal shark attacks in a particular year is around 1 and suddenly there's a year during which 4 people get killed, everyone (including the media) immediately assumes that sharks are increasing in number at a rapid rate. No one stops to think that sharks can't grow to man-eater size in a single year, quickly enough to bolster the number of man-eaters by 400% from one year to the next.

Yes, I see this every day, on MANY subjects.

[smy_749]

Yea I agree about the several hundred thing, even if it shows up as a 1.2 trio but you've only tested it 10 or 20 times, you still haven't ruled out coincidence or other factors. Thats why I said you could look into it, not "you have discredited all science with your breakthrough research techniques based on opinion and sound intellect"

I'm not big on statistics honestly, I'm aware they play a huge role in science, but people just play with them too often for some other agenda. 1 Shark a year, thats not so bad, pretty safe *goes swimming*. When in reality it could be a pattern where every few years they migrate to that area and eat 20 tourists, and the in between years are 0 occurrences.

P.S. The earth is flat.

[crocdoc]

I'm not big on statistics honestly, I'm aware they play a huge role in science, but people just play with them too often for some other agenda.
Well, you can't really play with proper statistics, but it is easy to play with people's misconceptions of statistics and that is what people with an agenda do.


1 Shark a year, thats not so bad, pretty safe *goes swimming*. When in reality it could be a pattern where every few years they migrate to that area and eat 20 tourists, and the in between years are 0 occurrences.
Well, except that the 1 fatal attack per year stat is for a whole country, which is completely surrounded by water (Australia) so that's a strange migration (from elsewhere to a whole country, or even to the southern half of a country since most of the shark attacks are in cooler water). You'd also be suggesting a random migration pattern, in which large numbers of sharks get together and migrate every few years, but the number of years in between these migrations is random. That would be highly unlikely for a biological system.

:) See? Earth is round again.


,

[smy_749]

I agree, although you can use statistics which have no relevance because you didn't have any controls. There was a study about eating icecream causes Polio in the united states because the statistics said that both polio and icecream sales increased in the summer time, so polio must be caused by icecream. Or maybe that just proves your point of using them incorrectly, I don't know but its still funny.

Also about the shark thing, I forgot you live in australia. I don't know much about sharks but from watching enough discovery channel stuff, I know that a few species around the continental U.S. do migrate, where and for what reason I'm not sure. Also I didn't mean random, I just meant perhaps they come back every certain number of years for something (maybe to breed like salmon, or sea turtles or whatever). I need to brush up on my shark knowledge I guess :-P.

I just thought of a better example, because it was happening miami beach or something. A group of sharks which normally shows up on the shore earlier in the spring, before tourists start piling in for spring break, showed up during spring break this year due to changes in weather patterns. So maybe random weather events (which are likely unlike random biological) could cause this.

[crocdoc]

Or maybe that just proves your point of using them incorrectly
Bingo. That was exactly my point. The abuse of statistics, such as somebody trying to make a correlation between two unrelated (but perhaps, individually, perfectly legit statistics) doesn't make the statistics themselves bad. That's a Kent Hovind favourite trick, combining unrelated stats to tell a fable. It works on the mathematically dim. One of my favourites (done in jest) is on venganza.org, relating to the inverse relationship between global warming and piracy (if you're keen, go to venganza.org, click on About and then click the link to the open letter to the Kansas School Board and scroll down).

Regarding the shark thing, your spring break example was in reference to a known event that had been moved because of weather. Consequently, being a known occurrence the change in timing was recognised as such (which is how you were able to read about it).

I know what you were getting at - perhaps there's a pattern here in Australia that we haven't identified as of yet. Not in this instance, for the pattern would have to be random. People have been keeping stats on shark attacks, so graphs are readily available. The public tends to concentrate on the tiny peaks from one year to the next, but forget the big picture (loads of little peaks and troughs which, when one stands far enough away, shows up as a pretty straight line). Keep in mind that the numbers we are talking about are very low. One fatality for a population of 30 million per year is an incredibly small percentage so there's a fair bit of 'play' before changes start approaching significance.

[smy_749]

understood.
You guys only have 30 million? Is it hard for people to get permanent residence in australia, thats a serious question...or even a visitor visa?

[infernalis]

Not to distract too much, but skewing statistics is a government favourite here.

Millions upon millions of law abiding people own guns, but one nut case every half decade, the government makes it sound like a war zone.

[murrindindi]

understood.
You guys only have 30 million? Is it hard for people to get permanent residence in australia, thats a serious question...or even a visitor visa?


Hi, it`s not hard to get a visitor`s visa, much more dificult to get permanent residence (certain age range, occupation, minimum ammount of money, etc). Is it worth trying for the latter? You bet it is!!!! :yes:
So when are you planning on going (at least for a holiday)?

[smy_749]

Hi, it`s not hard to get a visitor`s visa, much more dificult to get permanent residence (certain age range, occupation, minimum ammount of money, etc). Is it worth trying for the latter? You bet it is!!!! :yes:
So when are you planning on going (at least for a holiday)?

When I finish school, and save a bit of money. Probably in the winter, which would be your summer right?

[murrindindi]

When I finish school, and save a bit of money. Probably in the winter, which would be your summer right?


In the temperate states our summer is from november to february (here in England, it`s one or two days every few years)..... (Or so I`m told, I`ve haven`t noticed it yet)... :no:

[infernalis]

Hi, it`s not hard to get a visitor`s visa, much more dificult to get permanent residence (certain age range, occupation, minimum ammount of money, etc). Is it worth trying for the latter? You bet it is!!!! :yes:
So when are you planning on going (at least for a holiday)?

Gee, only a couple hundred years ago, all one had to do is commit a crime to get permanent residence.

[murrindindi]

In the temperate states our summer is from november to february (here in England, it`s one or two days every few years)..... (Or so I`m told, I`ve haven`t noticed it yet)... :no:

Silly me, november is still spring, let`s try DECEMBER is the start of summer (it felt like summer when I went home last november, that`s what caused the mistake).... :wacky:

[smy_749]

Silly me, november is still spring, let`s try DECEMBER is the start of summer (it felt like summer when I went home last november, that`s what caused the mistake).... :wacky:


I'm confused, are you australian living in australia or...I thought i read that you were living in England or something.

[murrindindi]

I'm confused, are you australian living in australia or...I thought i read that you were living in England or something.


In spite of not knowing when summer starts, I was born near Perth, W.A, grew up in Melbourne, Victoria, but have been living here in the U.K for some years which means I`m still an Aussie and always will be! :yes:
I have some family here, which is why I am still here (it`s o.k, but not really "home").

[crocdoc]

You guys only have 30 million?

Actually, it's only 23 million.

Less the one that gets taken by a shark every year. ;)

[smy_749]

In spite of not knowing when summer starts, I was born near Perth, W.A, grew up in Melbourne, Victoria, but have been living here in the U.K for some years which means I`m still an Aussie and always will be! :yes:
I have some family here, which is why I am still here (it`s o.k, but not really "home").

Ah ok nice, I was born and raised in the same town, same neighborhood...andddd not much for herps, although I'm sure England is pretty much the same. Connecticut is probably one of the most boring, unknown states in the U.S