Mule Gives Birth

!splut writes "Thumbing it's nose as science, a Moroccan mule has given birth. Mules, hybrids between horse and donkey, are normally infertile, due to differences between the number and structure of horse and donkey chromosomes. Nevertheless, for reasons not well understood, fertile mules do occur, infrequently, with some 60 documented live births since 1527."

Comments

Offspring fertile?

[crow]

So what is really interesting is whether the offspring are fertile. If so, then we can start breeding mules from mules, and we have a new species.

And where does the infertility in mules normally lie? Is it a male thing or a female thing? Or both?

Re:Offspring fertile?

[geoswan]

So what is really interesting is whether the offspring are fertile. If so, then we can start breeding mules from mules, and we have a new species.

And where does the infertility in mules normally lie? Is it a male thing or a female thing? Or both?

I looked into this when we discussed cloning Mammoths, or harvesting frozen Siberian Mammoth sperm a few months ago.

It was my impression that the very rare offspring of a mule mare and a horse sire, or a mule mare and a donkey sire, are the same species as the father. The mule has a mixture of donkey and horse chromosomes. Sperm and ovum are haploid cells -- they have one chromosome, not a pair. That is how sexual reproduction works. It was my impression that most ovum will have a mixture of horse and donkey chromosomes. But very occasionally, by chance, an ovum will have entirely horse chromosomes or donkey chromosomes.

Male mules are almost always gelded, to curb their agressiveness.

Hobbyists cross donkeys with zebras. They call the offspring "golden zebras". Hobbyists cross lions and tigers. These crosses are, apparently, a bit nuts. Lions are, of course, social. And tigers are, of course, solitary. The hybrid is drawn both ways.

The Moroccan foal looks a bit like a baby donkey and a bit like a baby mule - but not exactly like either.

The site I found about crossing cats talked about the differences between lion tiger crosses where the lion was the mother and when the tiger was the mother. When the tiger was the mother the hybrid is larger than a tiger. The maternal influence on the foal's embryonic environment has an influence on how the genotype is expressed.

Another anecdote. You can tell whether a mule's mother was a horse or a donkey by putting it in a corral that contained both donkeys and horses. The mule will go hang out with the kind of animals it was raised with.

Re:Offspring fertile?

[Tackhead]

> Hobbyists cross donkeys with zebras. They call the offspring "golden zebras". Hobbyists cross lions and tigers. These crosses are, apparently, a bit nuts.

Okay. That's it. That's the last time anybody on Slashdot ever gets away with saying "Building a watercooled PC rig out of Kraft Dinner and installing cold cathode lights in their hard drives? Those silly PC hobbyists have too much time on their hands!" :)

Re:Offspring fertile?

[!splut]

So what is really interesting is whether the offspring are fertile. If so, then we can start breeding mules from mules, and we have a new species.

And where does the infertility in mules normally lie? Is it a male thing or a female thing? Or both?

The infertility arises from the fact that normally, during meiosis (the production of sex cells), like chromosomes in the diploid compliment of chromosomes (one chromosome from each parent) pair up, separate, and produce haploid daughter cells. Mules are in the awkward position of having 31 chromosomes from the donkey parent and 32 from the horse parent, giving them an odd number of chromosomes total, even though they are in a diploid state.

On the one hand this gives the mule "hybrid vigour" - it exhibits many of the desirable characteristics of each parent. On the other hand, this odd number of chromosomes poses problems for meiosis - the normal meiotic process just doesn't produce viable sex cells. (So, in answer to your question, the infertility is a male and female thing.)

The fact that the foal was born at all suggests that the mother, the father, the foal, or some combination has some manner of chromosomal aberration - an extra chromosome from one parent, or something along those lines - resulting ultimately in a viable diploid zygote.

Chromosomal aberrations often result in infertility to begin with... but lets pretend that the foal is fertile, and is able to breed with horses, donkeys, or future siblings. It's offspring will not exhibit the hybrid vigour that is observed in the mule, because the offspring will not have the characteristic compliment of horse and donkey chromosomes. And since that vigour is the reason why people breed mules in the first place, a new breed of fertile mule would not be that useful.

Not again

[Boglin]

The Second Foundation barely saved the Seldon plan from the Mule the last time. This kid could ruin everything!

Fertility

[ktulus cry]

One possible explantion for this rare occurance, one that I can see, anyway - Horses have 64 chromosomes in their normal diploid state, with haploid gametes having 32. Donkeys have 62 chromosomes in normal diploid state, with haploid gametes having 31. This gives a mule 63 chromosomes. If one gamete had experienced non-disjunction during meiosis (that is, one pair of homologues did not split correctly, giving one daughter cell 2 copies of a chromosome, and one none), a mule could have 62 or 64 chromosomes (depending on which gamete it received). This is not a very rare occurance, Down Syndrome or Kleinfelter's Syndromes in humans (trisomy 21 and XXY respectively). While most cases of non-disjunction produce abnormal offspring, in humans, for example, an XXX female is completely normal, except for a usually smaller stature. A case like this, where the offspring IS normal, is relatively rare, and a similar situation could be occuring in these fertile mules.

Speciation

[f97tosc]

The truth is that speciation is not very well understood. In many ways 'species' is a convenient abstraction - we humans like to put horses and donkeys into two discrete buckets and not think much about anything in between. In reality there is no law of nature that says that all living entities must belong to exactly one of our convenient buckets.

The 'infertile children' definition works pretty well, but it is not perfect. Another problematic example is that of a species of birds that live in different territories around the globe. The birds can mate with other birds in their own or in adjacent territories. In other words, the birds in the first territory can mate with those in the second territory, and those in the second with those in the third, and so on all the way around the globe - and finally the birds of the last territory can again mate with those in the first. However, it turns out that the birds cannot mate with birds several territories away. Our convenient species definition breaks apart.

Tor

A Mule giving birth

[kcavness]

Now that's some half-assed science.

No explanation != failure of Science != a miracle

[geoswan]

Let me tell you about another miracle.

My parents met in Venezuala, working for shell oil, in the late 1940s. Shell had a company store where the North American employees could buy stuff you couldn't normally get in Venezuala. They had North American bungaloes for the North American employees. They had a little school with a North American teacher (my mom) for their children.

Like other North Americans my parents had a local cleaning lady. Unlike some of the other North Americans my parents learned Spanish.

My mom told how she taught Dahlia, how to prepare potatoes North American style. Including baking them. You peirce the skin so the steam can escape. I know most people do this by poking them with a fork. But in my family we cut a small X in the skin.

My mom's spanish wasn't yet sufficient to explain why you cut an X however.

A couple of days later there was an explosion in the kitchen. Dahlia is standing over the oven door, covered with exploded baked potatoe.

She was hysterical, and very apologetic. She told my mother that she realized she must have been very religious. But, she was in a hurry, and just this once, she thought that God would forgive her if she blessed the potatoes by putting the sign of the cross in them after they were baked, not before.

Dahlia couldn't explain this explosion, except to think it was a miracle. God punished her for not blessing the potatoe with a cross.

So, was it really a miracle? Of course not. Does an inability to explain a phenomenon mean that it is the reuslt of supernatural intervention? Of course not. Not with exploding potatoes, or with unexplained births.

Re:The reason for sterility == odd chromosomes?

[geoswan]

The reason for sterility given in the article has to do with if the hybrid creature has an even number of chromosomes.

The beeb and the British Mule org may have said mules are infertile because they have an odd number of chromosomes. But I am skeptical.

Here is an excerpt from a page about the Przewalski Horse

Some authorities feel strongly that the Przewalski horse is the ancestor of all modern breeds. Others point out that it is a different species from the domesticated horse, having 66 chromosomes as compared to the 64 of the domestic horse. They further point out that while crosses between the Przewalski and domestic horses result in a fertile hybrid, the offspring has 65 chromosomes. Subsequent crosses result in 64 chromosomes and bear little resemblance to the Przewalski. The Foundation for the preservation and protection of the Przewalski's Horse, in Rotterdam, the Netherlands, report that only a few Przewalski horses are tamable, in proportions similar to a Zebra.

So, even if this site is mistaken to say that the 65 chromosome hybrid is fertile, what if you crossed a 62 chromosome Ass with a 66 chromosome Przewalski's Horse? That hybrid would have 64 chromosomes. Would that make it fertile?

Re:Anyone mated mules?

[geoswan]

Yes, mules come in both male and female. Male mules are almost always gelded, prior to puberty. There is no advantage to keeping them intact. And, if they are not gelded they get very aggressive.

Horse mother, donkey sire - offspring is a mule. Donkey mother, horse sire - offspring is a hinny. Genetically indistinguishable from a mule. I presume the two different names predate modern genetics.

Mules are stronger, and more intelligent than horses.

Like mules, a hybrid of a zebra and a horse, or a zebra and a donkey, is infertile. Or a hybrid between any of the three species of zebra.

Fans of breeding exotic hybrids have dreamed up all kinds of "cute" names for the different crosses. Seems annoying to me.

Breeding exotic hybrids of endangered species seems very irresponsible to me. But there are people who do it. It seems to me that breeding a Liger or Tigon means you are wasting the reproductive potential of the parents. The Quagga is a recently extinct subspecies of Plains Zebra. There is a project to find Plains Zebras with the most Quagga like characteristics, and breed them, to try to restore them.

This seems like a bad idea to me too. It seems to me that it makes more sense to husband the remaing genetic heritage of the Plains Zebra.

The sixth surviving equid is the very rare Przewalskis' Horse. Extinct in the wild. 150 survive in zoos. Originally found in Mongolia. It is not too late to try to preserve this animal's genetic heritage.