View previous topic | View next topic

Komodo dragon

Page 1 of 1

138476.  Wed Jan 24, 2007 9:29 am Reply with quote

A female Komodo dragon which laid fertilised eggs despite being a virgin is now a mother and "father" of five.

"As Komodo dragons can live for over 40 years, we want to get the names just right,"

......Quick, somebody call Blue Peter!

138482.  Wed Jan 24, 2007 9:35 am Reply with quote

That says that all of the hatchlings were male. I'd be interested to know how that happened since there was no male to provide a Y chromosome. I would have assumed that any eggs the mother produced would be female (two X chromosomes).

138487.  Wed Jan 24, 2007 9:54 am Reply with quote

grizzly wrote:
That says that all of the hatchlings were male. I'd be interested to know how that happened since there was no male to provide a Y chromosome. I would have assumed that any eggs the mother produced would be female (two X chromosomes).

I was thinking that it could have been along the same lines as in crocodiles i.e. temperature.

However after reading this... the plot thickens.

If Komodo dragons determined their sex by temperature, females who cloned themselves might produce sons if their eggs happened to be incubated above the threshold temperature. Unfortunately for this theory, however, sex determination in Komodo dragons is not done by temperature as in crocodiles, but by chromosomes, as in birds and mammals. This knocks on the head any suggestion that a female could produce sons by cloning. The clonally offspring of a female dragon would have the same sex chromosomes as her, and would therefore have to be of the same sex.

But New Scientist failed to mention a third possibility. Virgin birth can come about through 'selfing', as is common in plants, and that is not the same thing as cloning. Cloning, for instance in the famous sheep experiment, means making a new sheep (Dolly) from one of the diploid body cells of the old sheep (unnamed and unsung, poor thing). The two sheep in that experiment were equivalent to identical twins but of different ages, and they of course had to be of the same sex. Selfing is different. It is as though an individual mates with it. Two haploid (one set of chromosomes) cells from the same individual, one of them behaving like a sperm and the other like an egg, join together restore the diploid (doubled up) number of chromosomes. It doesn't have to happen like this, but if the two haploid cells that 'mate' have been formed by one haploid cell splitting into two, they will be identical to each other. The diploid baby will have a set of paired chromosomes in which every chromosome is identical to its pair, but not identical to the corresponding chromosomes of other babies in the clutch. The chromosomes of each baby, in other words, will be a set of matched pairs, but its siblings will each have a different collection of matched pairs. To use the genetic jargon, every baby will have 'zero heterozygosis' but in a different way from its siblings. And to put it another way, although the baby is diploid, with doubled up chromosomes, it might as well not 'bother' with the second of each chromosomal pair because it is identical to the first.

Now, what sex would the babies be, if they were the products of selfing? Here is where it gets interesting. If a woman reproduced by selfing, the child would have to be female. Female mammals have two X chromosomes while males have one X and one Y. Every human egg has an X chromosome, while sperms are of two kinds. 50% of sperms have a Y chromosome and the other 50% have an X chromosome. If an X sperm fertilizes an egg (necessarily X) the result is a female (XX). If a Y sperm fertilizes an egg, the result is a male (XY). You can quickly work out why this mechanism produces sons and daughters in equal frequency. And now, to answer the question about selfing. A human female has no Y-chromosomes. Every baby produced by selfing would have to be XX and therefore female.

But with some animals, such as birds and butterflies, the system works the other way around. Females are (the equivalent of) XY and males (the equivalent of) XX. They are actually called W and Z instead of Y and X, but the principle is the same. Now, think what the result would be if a female bird reproduced by selfing. She produces both Z egg cells and W egg cells. If a Z cell split and 'mated' with itself, the result would be ZZ and therefore male. Theoretically a W cell might split and 'mate' with itself to make a WW individual but that combination is unknown in nature (for good reasons which could occupy another Tale) and presumably would not survive. Therefore, if a female bird could reproduce by selfing, the offspring would all be male.

Komodo dragons are like birds in this respect. Males are ZZ and females are ZW. True clones of a female dragon would be ZW and therefore female. But if a female dragon reproduced by selfing, the surviving offspring would all be ZZ and therefore male. This is indeed the result observed. The hypothesis of selfing in Komodo dragons looks good.

The new paper in Nature adds powerful supporting evidence. Watts, Buley, Sanderson, Boardman, Ciofi and Gibson looked at the DNA of two female Komodo dragons, Flora in Chester Zoo and the already mentioned Sungai in London Zoo, and their parthenogenetic (all male) offspring. Exactly as expected, the babies within any one clutch were homozygous at all loci ('matched pairs' of chromosomes). Again as expected, they were not clonally identical to each other or to their mother but, again as expected, they did not have any genes not possessed by their mother. The genome of every baby, in other words, was a proper subset of its mother's genome, but a different subset from its siblings' genomes. The selfing hypothesis is upheld.

It has been suggested that, like some insects, Komodo dragons in the wild use sexual reproduction when they can, but females resort to virgin birth whenever they find themselves without a male. They are good swimmers capable of crossing from island to island. A female who found herself alone on an island could theoretically give asexual birth to sons, then mate with them to produce daughters as well as sons and thus colonize the new island.

Extract from:,452,The-Komodo-Dragons-Tale,Richard-Dawkins

gerontius grumpus
139630.  Sun Jan 28, 2007 9:45 am Reply with quote

With birds it's the males that have the XX chromosomes and the females that have the XY, could it be the same with reptiles?

Hans Mof
139659.  Sun Jan 28, 2007 10:40 am Reply with quote

gerontius grumpus wrote:
With birds it's the males that have the XX chromosomes and the females that have the XY, could it be the same with reptiles?


While male birds are the homogametic sex they don't have XX chromosomes. With Birds, some fishes, and some insects the ZW sex-determination system is used. Therefore, males have ZZ chromosomes and females ZW.

Next to the XX/XY and the ZW determination system there are two more chromosomal detremination systems: XX/X0 (a variant of the XY system in which the 0 stands for the absence of a second sex chromosome), and the haplodiploid system (found in ants and bees).

There are many other sex-determination systems around such as:

- determination by temperature at which the egg is incubated
- sex change through aging
- sex determination by bacterial infection (Wolbachia)

gerontius grumpus
139794.  Sun Jan 28, 2007 6:41 pm Reply with quote

When I was at college, 1977-1980, they hadn't thought of calling them Z&W instead of X&Y.

QIly, many ofthe fast growing rainbow trout that are used to stock put and take fisheries are triploid or tetraploid and they are said to be all female.

140062.  Mon Jan 29, 2007 2:48 pm Reply with quote

That's fascinating - thanks guys.

285317.  Tue Feb 26, 2008 2:17 pm Reply with quote

there are many other options to inheritance: such as linked X^X chromosomes which are passed together to the progeny instead just 1. maternal effect and cytoplasmic inheritance should be kept in mind aswell, and ofcourse recombination which passes genes between homologous chromosomes.
truly yours,
Rake the Pigeon

556827.  Tue May 19, 2009 9:59 am Reply with quote

Also in the New Scientist, a report that Komodo dragons are actually venomous.

The venom gland "is not a trivial structure, [but] a big bulge" on the lower jaw, says Fry, who compares previous ignorance of the Komodo dragon's venomous capabilities as akin to "missing the teeth on great white sharks and saying they are plankton eaters".

650857.  Tue Dec 29, 2009 4:52 pm Reply with quote

The Komodo Dragons' prey today are introduced goats, buffalo and other animals. So what did the dragons prey on before human settlement? The answer is quite interesting as it was a species of pygmy elephant (now extinct)!

751526.  Tue Oct 12, 2010 4:54 pm Reply with quote

A recently discovered relative for the Komodo Island Dragon has been found on an island in the Moluccans.

Explorers have recently discovered a new species of monitor lizard, a close but smaller relative of the Komodo dragon, on the Moluccan island of Sanana Indonesia.

The Torch or Sago Monitor, has a bright orange head with a glossy black body. It can grow up to four feet in length, and thrives on a diet of small animals and carrion.

Reports from New Guinea suggest that a large lizard may await "discovery". People who claim to have seen it say it is very large in size.

808106.  Fri Apr 22, 2011 3:03 am Reply with quote

Recent studies show that the Komodo dragons female can have babies whittout having sexual contact with a male like in the Zoo for example. This rare phenomenon is called Parthenongenesis. If you want to know more, I can try to help you. You can also look on this website:

Have a good day!

808285.  Fri Apr 22, 2011 10:07 am Reply with quote

Thanks berlingirl and welcome :-)

814238.  Sat May 07, 2011 2:42 pm Reply with quote

Continuing the thread of this theme given the dangerous nature of these creatures it is probably just as well "virgin birth" is possible. I can imagine the reluctance of a potentially randy male dragon to approach a female (especially in a bad mood).

Ai in captivity may be difficult or even dangerous without extreme sedation of male and female!


Page 1 of 1

All times are GMT - 5 Hours

Display posts from previous:   

Search Search Forums

Powered by phpBB © 2001, 2002 phpBB Group