parthenogenesis

Termite queen avoids inbreeding by leaving a legacy of clones

edyong — Fri, 27 Mar 2009 07:30:34 +0000

Termite queen avoids inbreeding by leaving a legacy of clones

Termite colonies are families - millions of individual workers all descended from one king and one queen. But the colony itself tends to outlast this initial royal couple. When they die, new kings and queens rise to take their place. These secondary royals are a common feature of some families of termites, and they will often mate with each other for many generations. But there is more to this system than meets the eye.

Kenji Matsuura from Okayama University has found that the secondary queens are all genetically identical clones of the original. There are many copies, and they have no father - they developed from unfertilised eggs laid by the first queen through a process called parthenogenesis. These clones then mate with the king to produce the rest of the colony through normal sexual means.

It's a fiendishly clever strategy. The original queen's legacy to the colony is... herself. She effectively splits herself into several different bodies and in doing so, greatly increases the number of offspring she has. And because each of these descendants mates with the king, who has no genes in common with them, the colony neatly skirts around the problems of inbreeding.

Matsuura collected 30 natural colonies of a Japanese termite Reticulitermes speratus and they found that in all but one of these, the original queen had been replaced with several secondary ones - a total of 1,660 between the various nests. However, the majority of the colonies were still home to the original king, and the remainder had a single secondary one. This suggests that the king always 'rules' alone, and does so for a longer period of time than his mate.

When Matsuura analysed the genes of 135 secondary queens from seven different colonies, he found a surprise. Virtually all of them from any given colony were genetically identical to each other, and in the one where the original queen was still alive, her successors' genes were perfect matches for her own. And none of these termites had any genetic variants in common with the kings from their respective colonies.

Clearly, the first queen had spawned her successors without any help from the king. The same thing didn't apply to other members of the colony. Matsuura tested 20 workers from each colony and found that every single one was the product of sex between a queen and a king.

To confirm this, Matsuura checked for signs of inbreeding among the workers. Because the father and mother of inbred individuals are related, they have a higher-than-average chance of carrying the same copies of any given gene, as opposed to two slightly different versions. This wasn't the case for the worker termites - they had high levels of "heterozygosity", meaning that they frequently carried two different versions of the same gene.

This obviously benefits the queen. Even after she dies, she had effectively started an entire dynasty of herself, each of whom will produce huge numbers of daughters. And because these daughters are produced by the usual sexual congress between king and secondary queen, the levels of genetic diversity within the colony remain high. The king benefits too - it's likely that the offspring he sires by mating with the various clones of his queen will be healthier and fitter than those he would produce if he had to mate with his own daughters

Reference: Science 10.1126/science.1169702

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edyong Fri, 03/27/2009 - 03:30

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Excellent writeup. Am I the only one that wants to turn this into a scifi novel?

Maybe another pixar movie?

My mind is reeling with the implications for xenomorph reproductive strategies (Aliens films). :-)

So, what happens when the king dies? Does a new king from outside of the colony arrive, or does a king arise from the colony, mating with his mother (or a clone thereof)?

Awesome, but eerie stuff. Also, I had the same thought as Jessica. Go figure that out... o_O

In termites, are secondary queens exact clones? In other words, are the secondary queens products of a meiosis/recombination and joining of two meiotic products (producing nonidentical parthenogens)? Or are they produced by a single egg copying the chromosomes that it contains, producing total homozygotes (again nonidentical parthenogens)? Or are they actual clones, produced somehow with the exact same chromosomes as the mother?

It's good to be the king.

Sand dollars avoid predators by cloning themselves

edyong — Thu, 13 Mar 2008 13:01:00 +0000

Sand dollars avoid predators by cloning themselves

Many animals have cunning ways of hiding from predators. But the larva of the sand dollar takes that to an extreme - it avoids being spotted by splitting itself into two identical clones.

Sand dollars are members of a group of animals called echinoderms, that include sea urchins and starfish. An adult sand dollar (Dendraster excentricus) is a flat, round disc that lives a sedate life on the sea floor. Its larva, also known as a pluteus, is very different, a small, six-armed creature that floats freely among the ocean's plankton.

A pluteus can't swim quickly, so there is no escape for one if it is attacked by a hungry fish. Instead, Dawn Vaughan and Richard Strathmann from the University of Washington discovered that the pluteus relies on not being spotted in the first place.

They exposed 4-day-old larvae to water which contained mucus from the skin of a potential predator - the Dover sole. Within 24 hours, every single larva that was exposed to the mucus has grown a small bud that eventually detached and developed into a second larva, genetically identical to its parent and smaller in size. In contrast, larvae that were exposed to untouched seawater stayed undivided.

The tactic presumably works because hunters find smaller larvae harder to spot. As a result of the cloning process, the original larva halves in size. The newborn clones were smaller still and some were no bigger than a sand dollar egg cell, just an eighth of a millimetre across.

Almost all groups of echinoderms clone themselves in response to favourable temperatures and abundant food. In fact, asexual reproduction is a remarkably common tactic among plants and animals and is even used by some very unexpected species. It brings several advantages; by cloning itself, an animal can rapidly produce large swathes of offspring to make the most of plentiful times and over time, asexual reproduction can even allow a lineage to divert different copies of its genes to new purposes. But this is the first example of an animal using a virgin birth to defend itself.

Obviously, the tactic isn't meant to protect the young sand dollar against an attack - even the slowest fish would have made a mouthful of the dividing larva within 24 hours. It's more of a long-term strategy, allowing the larva to prepare itself for the presence of predators, as indicated by the smell of mucus in the water.

That's not something that adult sand dollars can do. From their position on the sea floor, they have scant information about the risks that their young plutei may face and cannot alter the size of their eggs appropriately. Instead, Vaughan and Strathmann suggest that the cloning tactic allows the larvae themselves to alter their size in response to indicators of risk.

Reference: Vaughn, D., Strathmann, R.R. (2008). Predators Induce Cloning in Echinoderm Larvae. Science, 319(5869), 1503-1503. DOI: 10.1126/science.1151995

edyong Thu, 03/13/2008 - 09:01

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Did she or didn't she? Genetic testing and virgin birth

sporte — Mon, 03 Dec 2007 08:00:00 +0000

Did she or didn't she? Genetic testing and virgin birth

'Tis the holiday season and, according to ancient lore, the time when miraculous events are most likely to take place.

One of those well-known and miraculous events of ancient days was the birth of a son to a young girl, who, although she was married (Okay, I'm not sure about this part of the story) she was said to be a virgin and the birth to be a miracle.

Hmmm.

How do you think the news would be received if that sort of thing happened today?

Certainly, if the young girl were to produce a grilled cheese sandwich with a burn spot that vaguely resembled a woman in a robe, someone might be able to sell it on Ebay and all kinds of people would consider it some kind of miracle (for many different reasons). But if the girl produced a baby, let's face it, most of us would question her ability to do this on her own without some kind of help. Some people might even consider using a bit of science to test her claim and find out if she was right.

Lizards do it

We do know, out there in wild, wild, kingdom of Omaha, that the virgins of some species can and do give birth. This phenomenon, called "parthenogenesis," has been documented in frogs, sharks, birds, mice, Komodo dragons, and Daphnia (1, 2). Sometimes, this occurs naturally, and sometimes parthenogenesis occurs when biologists mess around with eggs and test tubes. Whatever the cause, parthenogenesis involves activating an egg so that it develops in the absense of sperm. By knowing what's involved we can make some predictions that would help us test whether or not parthenogenesis has really happened (or not).

Girls, girls, girls

The first prediction we can make about virgin birth concerns the sex of the offspring. Human females are female because we have two X chromosomes. If we had even a single Y chromosome, we'd be male. Since a virgin mother only has X chromsomes, she only has the genes to make girls. So all children from a virgin birth, in humans, would have to be female (Uh oh! Keep in mind, I'm writing about science, not supernatural happenings).

Going farther

Okay, so virgin females can only give birth to girls. Lots of women who give birth to girls are not virgins. What other tests could we use to figure out if a girl is telling the truth?

We could use one of many different methods to look at the child's genotype. If the child is female, and the mother was a virgin, then most if not all of the child's DNA should be identical to DNA from the mother and every genotype that we examine in the child should be homozygous.

There are several methods that we can use to test this. The essential point is that every site we examine in the child's DNA should have two identical copies of the same sequence. Genotyping is a term that we use to describe looking at those similar positions. If we consider the DNA in our own chromosomes, sometimes we find that sequence is identical in both chromosomes and sometimes it's different.

One way to examine genotypes is by looking directly at the DNA sequence. In this DNA trace graph, you can see that most of the molecules have the DNA sequence
.

When we look at the next base though, at position 181, we see a green peak and a red peak on top of each other. This means that approximately half of the molecules had an "a" at position 181 and the other half had a "t." (We see this same pattern at position 184, too).

From these results, we can say that one chromosome has the genotype A and the other has the genotype T. Now, I don't which genotype came from the mother and which one came from the dad, but I do know that there are two different genotypes in this DNA sample.

If these data came from a sample of human DNA, we'd simpy have to grit our teeth and say "sorry kid, you may be miraculous, but your birth was not.."

References:

1. Edwards RG. 2007 "The significance of parthenogenetic virgin mothers in bonnethead sharks and mice." Reprod Biomed Online. Jul;15(1):12-5. Review.

2. Chapman DD, Shivji MS, Louis E, Sommer J, Fletcher H, ProdÃ¶hl PA. 2007. "Virgin birth in a hammerhead shark." Biol Lett. 2007 Aug 22;3(4):425-7.

sporte Mon, 12/03/2007 - 03:00

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Genetics & Molecular Biology

I'm unsure of the mechanism of parthenogenesis, but I don't think being homozygous is a requirement. Given that the mother is heterozygous, and if each allele is a random choice from the mother's genes, some loci of the child will be heterozygous as well.

Additionally, due to mutations, we also can't rule out getting a physically male child from (natural) parthenogenesis. There is always a small chance that a hormone/sex development pathway will be mutated so as to cause an XX male to form. Exceedingly rare, but possible.

RM,

I guess I should have added a bit more explanatory information in my post.

Eggs are made through a process called meiosis. During this process, the number of chromosomes in each pre-egg cell gets cut in half. The egg that results only has a single copy of each chromosome.

During parthenogenesis, that egg, with it's single copy of each chromosome, gets stimulated somehow and the proteins inside that egg copy the egg's DNA, creating two copies of each chromosome. As a result, the egg now has two identical copies of each chromosome. All the cells that arise from that egg will also have two identical copies of each chromosome, and thus every chromosome is homozygous.

Now, as to the question of can we get a male child if we start with female chromosomes? I don't see how that could happen. Human females are only female because our genomes lack a Y chromosome. Even with mutations, you're not going to turn an X chromosome into a Y chromosome. And, if a child doesn't have an X chromosome, it will die. Consequently, the offspring must all be female.

Since a virgin mother only has X chromsomes, she wouldn't have the genes to make girls.

You might want to correct that sentence. :)

As for the mechanism for parthenogenesis, do we know for sure it involves meiosis at all? Testable hypothesis - are the parthenogenetically generated komodo dragon girls really fully inbred? At least in pythons, they appear not to be so.

Sorry, failure of logic.
(I am not Christian, not religious, in fact atheist)
You are arguing from a non-theist point of view. The Christian response would be: GOD can do anything he wants. The laws of genetics do not apply. So all you can do, if you could examine Jesus' DNA, is prove parthenogenesis, you cannot disprove it. The other DNA would be GOD'S.

Marriage requires consummation. In the story, the mother wasn't married at the time of conception, and was still unmarried at birth, making the baby a bastard.

Gustavo: thanks for catching that. The error is fixed. With X chromosomes, you can only make girls.

Now, back to the Komodo dragon story, in the Nature paper last December, all the sites that were tested were homozygous. However, only 7 sites were tested in the paper, so you could argue that a more thorough examination is warranted.

As to the question of meiosis, my literature scan shows that people have only been able to find parthenogenesis happening in mammals is when they've taken extraordinary in the lab to make it happen. These cases generally involve using an ooctye (egg cell) and adding extra DNA or stimulating it somehow to make it divide.

I have to look at this paper a little further, but it looks like nematodes produce homozygous offspring.

The best known example of this in vertebrates is in the lizard genus Cnemidophorus, where multiple species are parthenogenetic.

The daughters are all clones of the mothers in the research that has been done to date

Thanks Marian!

I have to agree with Karl. The concept of "virgin birth" only means that there was no sexual intercourse and her hymen was not broken. There are other ways to fertilize her egg known to science nowadays. Bible even mentions that Jesus was a "Son of God", so there was a male parent. It does not have to be parthenogenesis. Let's not unnecessarily complicate things.

Thanks for the clarification on the mechanism of parthenogenesis.

Although a Y chromosome (specifically the SRY gene on it) is usually the defining factor in human sex determination, the physical "symptoms" of maleness are actually determined by a complex hormone cascade. There is a condition called XX male syndrome (de la Chapelle syndrome) where a patient is physically male, despite having no Y chromosome. Most of those cases are due to the translocation of the SRY gene from the Y chromosome to another chromosome. (This, of course, would require male involvement.)

There are, however, a small fraction of XX males who are SRY negative. I can't find details on the biochemical processes which underlie SRY negative XX male syndrome, but I imagine that it probably involves some mis-regulation of the sex determining hormones. Given that we know homozygous (highly inbred) individuals are more sensitive to genetic defects, there is a possibility that a human female would carry one or more recessive mutations which would cause SRY negative XX male syndrome, if homozygous. Alternatively, there could be one or more dominant mutations induced in the germ line after the mother developed, but before the parthenogenic infant does. Granted, this would be exceedingly rare (especially coupled with the chance of parthenogenesis), and definitely not the first possibility one would jump to, but we can't rule it out with a simple "Y = male" type analysis.

RM: I knew about SRY translocations but I didn't know about the other SRY negative XX cases. Do you have a reference? That's really interesting!

To date, no one has ever documented parthenogenesis in mammals, except under laboratory conditions where people have taken extreme measure to try and make it happen.

Since parthenogenesis in mammals must be a rare event, if it even occurs in nature, and SRY tranlocations are also very rare events, I thought it best to stick with the case that would be most likely to occur, if it were to occur at all.

S & Karl: I defined virgin birth as a birth without a male parent, which would be the same thing as parthenogenesis.

S.: I didn't know that a virgin birth could be defined in other ways. Are you suggesting that in vitro fertilization would result in virgin birth?

Karl: You're absolutely right that I'm using a non-theistic description. That's how science works. You're right, too. It never crossed my mind to imagine that a deity might have DNA. I wonder what that genome sequence would look like.

thanks for the comments!

I knew about SRY translocations but I didn't know about the other SRY negative XX cases. Do you have a reference? That's really interesting!

http://www.the-scientist.com/news/display/25087/ mentions the SRY negative XX male condition and some tests done on mice.

Congratulations Marian, when you said that the daughters are all clones of the mothers in the research done to date.
You hit the nail on the head.
A normal birth, that is male plus female germ cells, results in the offspring having a mix of DNA and chromosomes from both parents, right? and can be XX or XY.
In parthenogenensis, just from the very meaning of the word, we have offspring that are 'clones' of the one parent. They are produced from one batch of DNA.
So, if the clones are from the mother's somatic cell, they will be female, genetic copies of the mother.
However, if the cloned offspring, are cloned form a somatic cell of the father, and implanted in the female for gestation purposes, that is male DNA, XY, then the resulting clones would be male, as in the case of Jesus Christ, and would be genetic copies of their father.
Now the only thing is that in the case of Jesus Christ, we know he was the son of God, and it was a virgin birth, but we don't know if he was half God/half Mary DNA or all God DNA. He could have been either.
But if he was a clone, it would be all from his Father.
So his birth would be parthenogenesis, with two possible sources.

Sorry, I'm no scientist. But I am Catholic. Speaking for our understanding of the virgin birth (And I believe all Eastern Christians in this case), the idea of God's DNA is totally preposterous!

Christ is called the Son of God with regard to his Divinity (pre-existing his incarnation in Mary's womb) and the son of Man with regard to his human nature/his biology. So the idea of God having DNA as if God is a material being would be like the heresy of heresies in our churches, I'd presume. Are people actually suggesting that God had sex with Mary??? It's called incarnation because the idea is that God (a pure spirit) "took on human nature"- It wasn't his to begin with!

Mary was Christ's biological mother. How God provided for what a biological father would normally provide for, he has not told us. Perhaps he used this process you're describing, parthenogenesis, perhaps he just provided for the male chromosomes (a type of miraculous invitro, if you will)- He is lord over nature after all. But there's certainly no such thing as God's DNA- What a ridiculous thought!

Hammerhead Shark Had Immaculate Birth

zooillogix — Wed, 23 May 2007 12:10:00 +0000

Hammerhead Shark Had Immaculate Birth

Nuestra Tiberone de la Conception, Hammerhead shark, Sphyrna zygaena

A female hammerhead shark gave birth to a pup in the Henry Doorly Zoo in Nebraska in 2001 despite having no contact with a male shark. Thanks to new DNA profiling technology, scientists have been able to show conclusively that the shark pup contained no genetic material from a male. Before you whip out your Book of Revelations and start begging for forgiveness, you should know that this is an example of a naturally occurring phenomenon called parthenogenesis. In parthenogenesis, egg cells develop as an embryo without the addition of any genetic material from a male sperm cell. This reproductive process has been witnessed in bony fish before, but never in cartilaginous fish like sharks.

Asexual reproduction decreases genetic diversity, and thus can weaken a species as a whole. Witnessing the hammerhead's virgin birth is thus a cause of concern for scientists, worried about further weakening of already threatened shark species in the world.

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zooillogix Wed, 05/23/2007 - 08:10

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Sorry if this is off topic but Iâm thinking of buying this book. Curious if anyoneâs has checked out the new book âHellâs Aquariumâ by Steve Alten? I know heâs been a best selling author before, but wanted to see if anyone had read this book first? Itâs about the ancient prehistoric shark Megalodon, which makes the current Great White Shark look like a gold fish. Check out the trailer below, pretty awesome:

http://www.variancepublishing.com/meg-hells-aquarium-contest.html

I cant believe this is a fish !!!