Hello and welcome to a Fun Fact From Flora ,
CONTENT WARNING — this email contains images of fruit flies having SEX (audible gasp) you"ve been warned * * **
Today we are going to have a look at one of the very few examples of feminism in animal sex within the natural world. Cryptic female choice.
It sounds cool right?
I think this has come up in a fact before, but for a quick recap — cryptic female choice (or CFC to us kool kidsof biology) is a female-driven , post-mating mechanism that females use to systematically bias the fertilisation of her eggs in favour of a certain male.
This essentially allows females to have a say in the paternity of their offspring. This is pretty good for them, as in the animal kingdom there is a LOT of sexual coercion. So even though a female might be forced to mate with a male that she doesn’t want to, she can choose that that male does not fertilise her eggs.
PRETTY neat if you ask me.
This can be seen in jungle fowl (which kinda look like the wild ancestors of chickens).
Here, females will always mate with dominant males if they can. If subdominant males force females into having sex with them, the females will quite simply eject their sperm. They don’t want it. They won’t have it.
And they can eject up to about 80% of that sperm which is pretty badass!
Now put your biology hat on.
ANYWAY.
Now you"ve got your biology hat on we can think about this a bit more sensibly. How do we know that the spermfrom these subdominant males isn’t just a bit rubbish ? How do we know that it is the DOMINANCE of the males that is causing the ejection?
Well if you do some experimental jiggery pokery and change the social dominance hierarchy in the group (i.e. taking out the big dominant males so that subordinate males take over) then you see that the females CHANGE which sperm they choose to eject.
WOWZA.
A very interesting consequence of this is that it can lead to what we like to call runaway selection .
This means that if females keep picking males with certain qualities to fertilise their eggs, then that trait is going to get selected and amplified again and again.
This happens because females produce sons that have the trait and daughters that find the trait attractive so it gets bigger and bigger. This is why you have some crazy sexual ornaments that evolve
But this doesn’t only happen on the scale of a whole animal (like those photos above) but also at the gametic level — i.e. at the level of the sex cells themselves.
If you are a fruit fly (a Drosophila ) — I"m afraid that size does matter. CFC seems to select males that have longer sperm and the males that have longer sperm are also more likely to be able to displace any sperm from males that she might have already mated with. In one species, Drosophila bifurca , this has led to evolution of the longest sperm cell in the animal kingdom.
This little guy is 3mm long.
Wanna know how long his sperm cells are?
UP TO 58.3mm long.
YES THAT IS TWENTY TIMES HIS LENGTH.
That is like the average male human having a sperm cell that is over 30 METRES LONG. That’s a lot.
Hope you enjoyed and feel more empowered if you are a woman and more insignificant at the length of your sperm cells if you are a man.
Lots of love,
Flora
P.S. Here’s your animal-falling-over GIF.
