Female shark learns to reproduce without males after years alone | Hacker News Reader

Female shark learns to reproduce without males after years alone

newscientist.com

167 pointsperseusprime1150 comments

How exactly did she _learn_ to do this? Is there a shark manual on asexual reproduction that she has been boning up on?

She probably didn't and that makes the headline clickbait. At the end of the article it points out that we probably just haven't observed this because we aren't looking for it. Sharks are known to produce offspring asexually.

>One possibility was that Leonie had been storing sperm from her ex and using it to fertilise her eggs. But genetic testing showed that the babies only carried DNA from their mum, indicating they had been conceived via asexual reproduction.

In this form of asexual reproduction are the babies genetic clones of the mother?

From BBC via Google's infobox;

  Asexual reproduction needs only one parent, unlike sexual reproduction,
  which needs two parents. Since there is only one parent, there is no
  fusion of gametes and no mixing of genetic information. As a result, the
  offspring are genetically identical to the parent and to each other. They
  are clones.

I haven't figured out if it is all sharks or not, but apparently in many previous observances the offspring have only been half clones of the mother. The genes all come from the mother, the offspring just ends up with less genetic diversity than the mother. The technical term is "automictic parthenogenesis". https://en.wikipedia.org/wiki/Parthenogenesis#Automictic_par...

I did see once a documentary on a spider, where if there were no males to reproduce with, the female would hatch a single male spider that was a clone, and that spider would then fertilise her eggs before being devoured.

>just ends up with less genetic diversity than the mother

"just"...

In humans, even a small loss in genetic variability such as cousin mating 1.5% is bad enough that we have laws against it in nearly every society.

Charles II, the last Habsburg king of Spain, had lost 25% genetic diversity and was mentally and physically disabled, and infertile. This genetic loss is equivalent to parent-offspring or sibling mating.

Some animals, like lab mice, can survive without genetic diversity, but they are much less fit and difficult to raise. Your half clone would have lost nearly 100% of its genetic diversity. A near-full clone mechanism exists which would preserves genetic diversity. We'd have to sequence this shark to find out.

>In humans, even a small loss in genetic variability such as cousin mating 1.5% is bad enough that we have laws against it in nearly every society.

I thought this sounded suspicious, so I looked it up, and it's not true. Cousin marriage is legal in all of Europe, Australia and New Zealand, South America, Canada, Mexico, the Middle East, Russia, and India.

In The USA, cousin marriage is allowed in 17 states. But 40 out of the 50 states allow cousin sexual relations and cohabitations.

The only places in the world that cousin marriage is illegal is in China, Korea, Japan and some states in the US.

Whatever you think of cousin mating, it's just not true that "we have laws against it in nearly every society." In fact, just the opposite, it is allowed in nearly every society.

During my undergrad studies in anthropology, a prof remarked off-hand that the prohibition of first-cousin marriage a pretty new and baseless thing, and that the offspring were very negligibly at risk. It was an off-hand comment, but an off-hand comment made by someone with a PhD in the field, so I'm with her on this one. But now googling . . .

Genetic diversity is meaningless at an individual level.

An organism may end up with 2 copies of a defective gene and demonstrate problems. However, having two working copies of the same segment is not a problem.

"... parthenogenetic offspring may have anywhere between all and half of the mother's alleles. The offspring having all of the mother's genetic material are called full clones and those having only half are called half clones. Full clones are usually formed without meiosis. If meiosis occurs, the offspring will get only a fraction of the mother's alleles."[1]

[1] https://en.wikipedia.org/wiki/Parthenogenesis

If you're referring to the shark in the news article, her offspring are not genetic clones.

"In sharks, asexual reproduction can occur when a female’s egg is fertilised by an adjacent cell known as a polar body, Dudgeon says. This also contains the female’s genetic material, leading to “extreme inbreeding”, she says."

Which is odd because genetic clones would be far healthier than the inbred offspring from above.

Parthenogenesis...

https://en.m.wikipedia.org/wiki/Parthenogenesis

Parthenogenesis is a natural form of asexual reproduction, though pretty sure it is not the ONLY form asexual reproduction.

My guess is at this point it maybe unclear exactly what is going on.

"Mum’s genes get passed down from female to female..."

That's the clue. Female to female === Parthenogenesis.

Dr. Ian Malcolm: John, the kind of control you're attempting simply is... it's not possible. If there is one thing the history of evolution has taught us it's that life will not be contained. Life breaks free, it expands to new territories and crashes through barriers, painfully, maybe even dangerously, but, uh... well, there it is.

John Hammond: [sardonically] There it is.

Henry Wu: You're implying that a group composed entirely of female animals will... breed?

Dr. Ian Malcolm: No. I'm, I'm simply saying that life, uh... finds a way.

https://www.youtube.com/watch?v=kiVVzxoPTtg

Life imitates Art.

The author wrote life into the art. Amphibian DNA was stuck into the dinosaurs to make it harder for critics to criticize the parthenogenesis in the book.

Amphibian parthenogenesis is well documented:

https://en.wikipedia.org/wiki/Parthenogenesis_in_amphibians

The book did not feature parthenogenesis. It featured protogyny. Some individual females became male and bred with the individuals that remained female.

This has been observed in West African common reed frogs (Hyperolius viridiflavus), as a result of population pressure. If the pond is a taco fest, some of the frogs bring sausage.

This is actually more common in fish than in amphibians, but the book used amphibian DNA.

I'm confused why you are downvoted - you appear to be correct.

the taco fest sausage thing might have upset some people, I didn't downvote but does seem somewhat gross.

What he is saying is some creative male will find a way to enter that room.

While this is fascinating I still can't believe we still have never observed many shark species giving birth particularly Great Whites.

Learns how? Horrible title. As if the shark tried many times but finally discovered this one simple trick...

(serious question) Do any genetic algorithms take something like this into account? Seems like it could be a good way to increase the odds of furthering successful generations.

A lot of genetic algorithms already seed the next generation with copies of the top X fittest individuals, so it's essentially already done.

IIRC, it's common for GAs to have variability as the only source of variation, not crossbreeding. And those that do use crossbreeding usually don't have a concept of the "sex" of an individual algorithm. So, crossbreeding of what are effectively two haploid gametes (a polar body isn't exactly a gamete, but...) from the same diploid individual when mates of the opposite sex are in short supply isn't something that would be directly applicable to most genetic algorithms.

You could build a framework for evolving genetic algorithms where this would be relevant and meaningful, but I'm not sure there is any good reason to bother with all the complexity that would be necessary.

Gotcha. It's not that genetic algorithms are meant to emulate the real-world, but rather that they're inspired by it.

While possible, I imagine it would require carting around more baggage with each variation, and would also require you simulate scarcity. It's been a long time since I played with genetic algorithms a little in college, but I'm not sure they often model making it hard to find a mate.

Yeah, sure they could

> A female shark separated from her long-term mate...

Aw. Do most sharks exhibit long-term pair bonding?

Some possibly do (http://rsbl.royalsocietypublishing.org/content/9/3/20130003), but many of the animals that are said to be monogamous are only ever proven to be 'genetically monogamous'.

It's hard to prove whether one male's sperm simply outcompetes other sperm.

Judging from the Planet Earth series, the BBC tends to turn anthropomorphism up to 11.

We just don't know still the answer to this question.

Parthenogenesis. A word I first saw in a Canned Heat album (https://www.youtube.com/watch?v=YEaIiB4UV20 love the jaw harp solo!). Then I asked my bio teacher about it and she explained it. I figured it was something that only happened in "really simple organisms" but then learned it was not uncommon amongst some animals.

e.g. the New Mexico Whiptail Lizard, a.k.a. the 'Leaping Lesbian Lizards':

http://guardianlv.com/2015/06/lesbian-lizards-a-hybrid-speci...

They get the nickname because despite every member of the species being female (and, except for minor mutational differences, clones of each other), they still engage in faux-mating behaviour with each other --- they need the stimulation to ovulate.

Same situation, different band. Shriekback's 1985 song, Nemesis. [1]

Priests and cannibals, prehistoric animals

Everybody happy as the dead come home

Big black nemesis, parthenogenesis

No one move a muscle as the dead come home

[1] https://www.youtube.com/watch?v=BNA4MDc9U50&feature=youtu.be...

this was reported first in 2011: https://www.jumeirah.com/en/jumeirah-group/press-centre/pres...

The main point in this article was that the shark did this after having had babies with a mate before. That hadn't been observed in this species.

Probably stupid question, but I'll ask since others may have the same question: Would all the offspring in this case be female?

I'm blanking on my old biology knowledge that's stored somewhere in the cold storage of my brain haha

Depends on the sex determination system. XY vs ZW vs XO would determine it. XY would mean only female, ZW would mean both, XO would mean both or only one depending. Not sure what sharks are, some fish are ZW.

For the interested, ZW is the inverse of XY, while XO relies on X chromosome count to determine sex.

Like the other comment said, depends on the sex determination system. Which in fish can get complicated -- there are quite a few types of fish which undergo sex changes as a result of the environment they find themselves in. Anglerfish (which become male if they find an adult female early in life, otherwise female) are one well-known example. Clownfish are another: they live in hierarchical groups where the dominant fish becomes the lone female and breeds with the top male. If the female leaves or dies, the previous top male then becomes female and breeds with the previous #2 male.

Sequential hermaphroditism (sex changing) is in a different category. Sex changing fishes still need a partner to have babies. Not the case here.

Another posibilities could be that sperm where provided by other shark species in the same tank (The male DNA being discarded later) or that some chemical compounds where released in the closed water system, triggering the ovocite growth.

Finally, we could hypothesize that some old stored sperm could act as stimulus for oocyte division, even if the male cells were too old and damaged to be functional.

If you want to read some more about sex changing in fishes you can take a look to this article, for example:

P.Valdes, A.Garcia-Alcazar, I.Abdel, M.Arizcun, C.Suarez & E.Abellan. Aquaculture International. 2004, Vol 12(4). Seasonal Changes on Gonadosomatic Index and Maturation Stages in Common Pandora Pagellus erythrinus

(Yes, I'm the same P.Valdes)

Yes. There aren't any Y chromosomes available.

Male chromosomes aren't needed to make males.

Several kinds of fish change sex during their lives (as explained here: https://news.ycombinator.com/item?id=13430247). And in some types of insects any unfertilized egg develops male, allowing a lone female to produce a male offspring to mate with (at which point her fertilized eggs develop female).

And then there are reptile species in which sex is determined by the temperatures the egg is exposed to as the embryo develops. And then... and then...

Sex determination is way more complex and messy than people like to think it is.

Recommend reading https://en.wikipedia.org/wiki/The_Red_Queen:_Sex_and_the_Evo... if you are interesting in the topic. It goes way in depth into this and many other common reproduction strategies.

Fascinating, some reptiles and plants do the same.

Well I'll be damned.

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