An implied concept in taxonomy is that the further apart two animals are in their family tree, the less likely it is that they can produce hybrid offspring. This is part of how we define "species" in the first place and used to explain why, for example, breeding a cat and a dog together doesn't make catdogs: those are too different! This makes situations where hybrids
do result pretty fascinating, for example horse + donkey = mule/hinny. But again, it's fascinating because
it usually doesn't work. And while I just used a bunch of mammal examples, surely this is broadly true of the rest of the animal kingdom.
Enter some fish researchers in 2019.
Acipenser gueldenstaedtii the Russian sturgeon, and
Polyodon spathula the American paddlefish are two large and
extremely endangered fish. They are not particularly related, otherwise: they are both part of order Acipenseriformes, but that's kind of a broad group which boils down to "ray-finned fish that are like super ancient". The whole ray-finned fish group itself is already enormous and not very specific, so just because they're both janky living fossils doesn't mean they're RELATED-related. In fact, the scientists were working on both of them together BECAUSE they're not very related.
See, there's this absolutely bizarre type of sexual reproduction
1 some animals pull off called
parthenogenesis. This is when an organism which otherwise ought to engage in the traditional "two adults reproduce to create offspring" thing finds a way to do it solo. A famous example are whiptail lizards like
Aspidoscelis neomexicanus who are 100% female, males do not exist, yet the females carry on laying eggs which hatch into more genetically-identical daughters. "All females who keep cloning themselves" is not the only type of parthenogenesis, but it's one of the more common ones.
A to me even more puzzling subtype of parthenogenesis is called
gynogenesis. This is a type of parthenogenesis where the egg cell/final resulting offspring is a clone of the parent
but the parthenogenic process to turn the egg cell into offspring only starts if a sperm cell is present. Sperm has to show up to the egg but then it doesn't get used! For some reason! Because biology is a cosmic prank, I guess.
But despite my "it WHATS?" this is actually very convenient for certain amphibian/fish researchers. If you have, say, a big highly endangered fish, and you would really like to see if you can persuade it to clone itself, just get some sperm cells from a different big highly endangered fish and mix. If gynogenesis is possible this should trigger it, but if that doesn't work the two parents will be too different and the sperm won't fertilize the eggs! ^_^
...
New York Times, July 15 2020: "Scientits Accidentally Bred The Fish Version of a Liger.""
American paddlefish and Russian sturgeon were not supposed to be able to create hybrid offspring. Surprise!"
You know how it is with In-Vitro Fertilization, once you've got everything ready to go you might as well do as many eggs as you can.
Wikipedia: Hundreds of hybrid fish were created, of which about two-thirds survived over one month, and about 100 survived for one year.
So sturddlefish are a thing which can exist, it turns out.
The diagram on wikipedia is pretty fascinating: top/bottom are a sturgeon and a paddlefish respectively, for comparison, while the middle two are sturddlefish showing off the different genome
length results. Apparently the improbable babies either trip over their sturgeon chromosomes and end up significanly more sturgeon than paddlefish, or they keep the ratios even and look like an appropriately intermediate hybrid.
Anyways. As best I can find the little weirdoes have remained chilling in captivity in a lab with little expectation they'll amount to anything capitalism wants. But they do exist (or at least did for awhile) and I think that's cool of the fish and very hilarious of the humans.
- By sexual reproduction I mean: there are two types of organism reproduction, asexual and sexual. Asexual reproduction is what bacteria do: they just clone themselves, making a perfect copy offspring with perfectly identical DNA, without ever involving another bacteria in the process. Sexual reproduction is what butterflies do: two different indivduals meet up and combine their respective 1/2s of their DNA to make an offspring with the correct total amount of DNA but half of it was from one parent and half of it was from the other, making something new which is not a clone at all.
If you think parthenogenesis sounds like it should count as asexual, the trick is that (every?) organism known to do it is clearly descended from something which used to smash gametes with another organism and is still very much set up as if it expects to smash gametes with another organism. And then somehow jailbreaks that. So, technically counts as sexual reproduction, but in a very weird loophole way.
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