Today feels like as good a day as any to explore the phenomenon of parthenogenesis - "virgin birth". It's more common than you might think: a lot of animals do it. And they do it in different ways, for different reasons.
Parthenogenesis is a form of reproduction where no sperm is required to fertilise the egg. And it's *wild* how many different ways this happens in nature.
You have some species where their normal form of reproduction is parthenogenesis. Bdelloids, a class of rotifers, tiny freshwater animals, have got on very well without sex for up to 40 million years. It's just how they go.
Species which reproduce exclusively by parthenogenesis are all-female. And it's not just limited to tiny creatures which you can only see with a microscope. About 80 species of vertebrates are all-female and don't need sex to reproduce.
Special mention to whiptail lizards, who don't, strictly speaking, need to have sex to reproduce, but stimulate ovulation by humping each other nonetheless.
https://twitter.com/vagina_museum/status/1374352189376888833
Parthenogenesis can be a good strategy for invasive animals, because they can produce a lot of offspring pretty quickly without needing many of them to start with.
For example, the quilted melania, a species of snail which originated in Asia but is very good at establishing itself as an invasive species around the world, has males in some populations, but other populations produces entirely by parthenogenesis.
Marbled crayfish, which were once popular as pets, are incredibly good at establishing themselves invasively, because they're all female. If just one escapes, it can produce a population. They're now banned in many countries around the world.
And now we simply have to talk about aphids, who are incredibly competent at ruining your garden because they can reproduce very quickly indeed. Aphids use a blend of sexual reproduction and parthenogenesis, and it's the parthenogenesis which establishes them speedily.
A female aphid produces clones which are born live. These clones are born pregnant, with developing offspring inside them. And so on and on. Some species can produce over 40 generations in a single summer by speeding things along by giving birth to pregnant offspring.
They'll then produce some males for the autumn for a bit of sexual reproduction. The males are, again, produced through parthenogenesis - female aphids have two sex chromosomes (XX), while males only have one (X0).
And that's the thing: parthenogenesis doesn't always mean female offspring. Sometimes it produces males. And some animals lean into this.
Bees, wasps and ants use a mix of sexual reproduction and parthenogenesis. The queens of their colony need sex to produce female offspring (workers and more queens), but make males by parthenogenesis. In these species, males have half the total number of chromosomes of females.
Meanwhile, there's some animals who are capable of parthenogenesis and will *only* produce male offspring from this, due to their sex chromosomes. An example of this is komodo dragons.
https://twitter.com/vagina_museum/status/1427233247948427265
Komodo dragons don't use parthenogenesis as their main reproductive strategy: they do it in absence of males. It's been documented in captivity in several species, and can be a bit of a headache for zookeepers.
As well as komodo dragons, parthenogenesis in captivity has been seen in several species of snake and lizard, some sharks, and some birds. This year, two Californian condor chicks in a captive breeding programme were found to be the result of parthenogenesis.
The condor story is particularly fun because in both cases they were in a captive breeding programme, i.e. a climate designed for sex. And the mothers had had sex. But for whatever reason, the eggs they laid were unfertilised - their offspring were the product of parthenogenesis.
In the 1950s, Dr MW Olsen decided to lean into parthenogenesis in birds, and selectively breed turkeys to reproduce by parthenogenesis. While his experiment was reasonably successful, the first chick born in this programme was immediately eaten by his dog.
Spontaneous, natural parthenogenesis hasn't been recorded in mammals, although under lab settings it can be induced. The offspring often don't develop normally, although one experimental strain of fatherless mice ended up living longer than normal.
And there is at least one case of human parthenogenesis. A boy was born whose white blood cells contained no DNA of his father's. And his name was...
FD.
FD.
FD exhibited chimerism. Most of the cells in his body were a result of reproduction, and contained DNA from his mother and father, but some cells were the result of an unfertilised egg which started dividing.
Sometimes parthenogenesis is an accident. Sometimes it's a necessity. And sometimes it's a strategy which has served species well, for millions of years.
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