- Hey, everybody. Welcome back to my channel.
So I am very excited
to start diving into more videos
on different sex and relationships topics
but I also wanna talk about pregnancy
just a little bit more if you will indulge me.
So I recently had a baby
and experienced the whole pregnancy and birth thing.
And a while ago, one of my patrons,
Lisa, reached out with some ideas
for videos that she wanted to help research and write,
and one of them was all about pregnancy
in animals, mammals to be specific.
And I was so down to explore the subject.
The animal world in the realm of sex
and mating is something I really don't know a lot about
but I'm fascinated by.
So I am really excited to dive into this topic with you
and share everything that I've learnt.
Every species will do what it can
to maximise its success
in its reproductive process, even humans.
Things like craving specific foods
and the nesting instinct in pregnancy.
But what about for other mammals?
The animal kingdom is full of weird
and wonderful creatures
and the way they reproduce is fascinating,
from four-headed penises to natural sperm storage.
Just FYI, I'm going to using the terms male
and female to describe
these animals' reproductive categories.
Obviously, we can't ask them
what their genders are
and how they identify.
So I'm going to be using male and female
as that is what is in the science.
Thanks so much to Lisa for researching this video.
As I mentioned, she is a patron of mine
and she is a disabled scientist
and one of her favourite topics is reproduction
and she has found some amazing, amazing facts for us,
and she's also introduced me
to some of my new favourite terms,
and I'm excited to share them with you
as we get into this video.
Okay, so it's time to get nerdy
about mammal reproduction and science.
The basics.
There are three ways mammals reproduce.
Number one, eutherians, AKA placental mammals.
This is like humans and elephants,
and they have a placenta that provides nutrients
to the embryo in the uterus.
Number two, egg laying monotremes.
Their name is pretty self-explanatory.
These are mammals that lay eggs.
But there're only five species that do this:
the duck-billed platypus and four species of echidna,
which are anteaters.
Number three, pouched marsupials.
These mammals have very short pregnancies
and after birth, the young will climb up
into the mother's fur
and into a pouch and find a nipple and suckle.
So this is like kangaroos and opossums.
Okay, so let's first talk about eutherian mammals,
starting with the males.
As you'll likely know,
they have two different reproductive organs:
the penis and the testes.
However, these organs can be external to the body,
like in humans,
or internal and comes out at appropriate times,
like a dog's penis,
which is covered by a penile sheath,
except for when mating.
It's a bit of a scientific mystery
why external testes have evolved in some mammals.
There's a bit of a cost
versus benefit evolutionary calculation going on here.
Keeping the sperm and testes at a cooler temperature
outweighed the risk of damage
as they were external and so voila,
the scrotum is born.
Now the female eutherians.
Again, there are two main sections.
You've got the vagina, cervix and uterus,
and the ovaries and fallopian tubes.
And these are always internal.
When it comes to periods,
only humans, great apes and bats have them.
All other female eutherians will reabsorb their egg
in their estrous cycle.
Not all mammals have a menstrual cycle
the way that humans do
and the overarching term
for the whole cycle thing in mammals is the estrous cycle.
This is something I recently learned.
And pregnancy length in mammals is highly varied.
Nine months for humans,
19 days for mice, and almost two years for elephants.
So all of that is vaguely familiar
but now let's move on to some
of the more unusual things,
at least from a human perspective.
What even is normal?
I don't know anymore. I don't know.
The spotted hyena and the pseudo-penis.
So the female spotted hyena is eutherian
and they have a clitoris that is shaped
and positioned to be almost identical
to the male penis
and this is called a pseudo-penis.
It can become erect
and is used for things like peeing, sex, and birth.
The labia also fused and form a pseudo-scrotum.
They also don't have an external vaginal opening.
The distinction between the male
and the female genitalia is that females
have thicker and shorter genitalia
with more rounded glands.
The female retracts her clitoris during mating
and the male enters the created gap.
And both male and female hyenas have penile spines
that assist in this process.
And as the females have to actively retract their clitoris,
this blocks the ability of forced mating.
Moving on to egg laying mammals.
This group of mammals are known as monotremes,
which translates to single opening.
This relates to a single hole they have
known as the cloaca
and this is used for all of the things,
poo, pee, sex, how efficient.
They have the reproductive characteristics
of lizards, like the cloaca and egg laying,
but also, mammals like mammary glands.
So scientists bloody love them
because this is pretty unique.
All monotremes are found in Australia,
which is a unique ecosystem in its own right.
It's probably likely that there was some sort
of evolutionary advantage
to the development of egg laying
over a mammalian estrous cycle.
One of the advantages of egg laying,
for example, in birds means that the male
and the female birds can care for the offspring
and the female doesn't have to carry multiple eggs
inside her body.
And oh boy, how do I wish
I could have shared pregnancy with Dan.
So let's talk about the male echidnas.
This little guy looks perfectly familiar
but his genitalia has evolved
into what has been named in biological circles
as the weirdest mammalian penis.
Well done.
(audience cheering) (host clapping)
Big applause.
So they do have a penis but this is only used
for semen and they urinate out of their cloaca.
The echidna penis
is actually two separate penises joined together.
The whole penis has one shaft
but four heads known as rosettes,
which are used interchangeably during mating.
Whichever two heads were involved in the last mating
get a little rest whilst the other two get busy
and then they swap again.
Here's a drawing of it
as I'm not sure I can show you a photo
of a four-headed penis on YouTube,
even if it is educational.
But you can google if you're curious.
So this allows males to maximises their total amount
of time spent mating
because they don't have to rest in between.
Therefore increasing their chances of success.
Most of the time, their testes are internal,
rather than external
and they undergo a seasonal emergence during winter.
And seasonal emergence is one of my new favourite terms.
(host humming)
Now time to look at the females.
Once fertilised, the female monotreme develops an embryo
inside of the uterus for 2/3 of their gestation time.
While in the uterus, the egg has a softer shell,
which allows nutrients to pass between the mother
and the child.
Then they lay the egg,
which will hatch around 10 days later.
The young monotremes are known as puggles
and they are very underdeveloped when they are born
compared to the likes of a human baby.
And human babies, let me tell you,
are also very underdeveloped when they are born.
And the female monotreme doesn't actually have nipples
but has openings on their skin,
which act as mammary glands.
And the newly hatched puggle
with use its sense of smell to locate the mammary glands.
So that's the eutherians and the egg laying mammals.
And we'll get onto the pouch marsupials in a bit
but first, there's some other weird
and fascinating things about mammal reproduction
that I want to share.
First up, superfetation.
Superfetation is the holding of embryos at different stages
of development in one uterus.
It can be found as an anomaly in mammals, including humans.
This is when there's a gestational difference
in age of non-identical twins.
At most, a two-weeks' difference
and this occurs in about 0.3% of pregnancies
that are more than one foetus.
But it is a natural part of reproduction
in only these five species.
So superfetation comes hand in hand
with another concept called delayed implantation,
which we will come to,
which allows the female to practise cryptic polyandry
and there is another term that I love.
Cryptic polyandry.
Cryptic polyandry is the reproductive ability
to hide the paternity of your young.
This prevents males of the same species
from committing infanticide of the young
that is not theirs
because they don't know who's is whose.
So when conception occurs in one of these species
during an already active pregnancy,
it leads the uterus to be holding embryos
at different stages of development
that may have different fathers.
So another method used for cryptic polyandry,
as I mentioned, is delayed implantation.
Delayed implantation is when the embryo
doesn't immediately implant in the uterus.
Basically, hitting pause.
The embryo can be held in the uterus
for up to 11 months
and this happens in 2% of mammals.
The main advantage of delayed implantation
is that it allows for births and postnatal development
to happen in the most favourable conditions.
For example, the European badger
will hold embryos in the uterus
until December to February when they will implant,
triggered by the shorter length of day.
This means that the female can mate multiple times
with many, many partners,
increasing the likelihood of the young being healthy
and reducing the likelihood of infanticide by other males.
So from delayed implantation to delayed fertilisation,
AKA, sperm storage.
Many female animals practise the process
of sperm storage, which is the holding of unfertilized sperm
somewhere in the reproductive system.
For example, us humans can store sperm
that has been released inside for up to five days.
However, some sharks, up to two years.
The female bat, however, is the leader
in the mammalian world for sperm storage.
They can store unfertilized sperm inside their uterus
for up to six months.
The process of sperm storage is critical
to the marsupial species known as antechinus.
Mating occurs in a restricted three-week period
once per year
in late winter before the female has even ovulated yet.
Copulation can occur for 8 to 12 hours.
That means, yes, they are having sex for 8 to 12 hours.
And after the mating period,
few, if any, sperm remain in the male reproductive tract.
The female will then store the sperm in a special organ
known as the storage crypt for up to two weeks.
Storage crypt, another one of my new favourite terms.
Now, here's the real kicker with this species.
After the mating period and before the female has ovulated,
the entire male population dies
due to stress-induced suppression of the immune system.
What the actual fuck?
And then the female will ovulate shortly after this period
and they've got a whole bank of sperm in that storage crypt
ready to go.
So let's take a look at what is going on
with some other marsupials.
Marsupials have a short gestation time relative
to other mammals, around 8 to 24 days.
After they are born,
they instinctively crawl up their mother's fur
and find a teat where they will remain
for the rest of the gestational period,
which varies from species to species.
Because of this form of gestation,
a marsupial can become pregnant many times in succession,
resulting in multiple joeys that are all on a teat,
but at different stages of development,
which is where asynchronous concurrent lactation comes in.
This is the ability of a female marsupial
to provide milk to multiple joeys
all at different stages of development.
The milk is provided in three separate stages:
early, mid and late lactation.
The tammar wallaby is the most studied marsupial
in this area.
They have four nipples or teats
and each one can provide milk
at the appropriate developmental level
for each joey.
Think of it as each joey is allocated a nipple
where they stay until they are ready to leave the pouch.
And all of the different nutrients
that they need from that milk
will change over time for that one joey
on that one teat.
Okay, moving on to possibly one
of my favourite biological features,
and that is cryptic female choice.
Honestly, the terms for this area, love it.
Love it, excellent terms.
So cryptic female choice
is the female's ability to choose the father
of their offspring
and it comes in a few forms.
The ability of some species to choose who they mate,
such as the spotted hyenas and dating in humans.
What fun.
Another way is masking their estrous cycle,
essentially hiding the fact that they are fertile.
Sperm ejection.
Some females can discard sperm by ejecting it.
Outside of mammals, the female cricket
can mate multiple times
and then discard the sperm of the unpreferred males
and retain the sperm of the preferred mate.
Destroying stored sperm by various means.
This could be by raising pH
or releasing certain chemicals.
And the mating plug.
In various mammals,
the male can leave behind a plug
in the female reproductive tract
and this prevents mating with other males.
However, some females have adapted the ability
to choose which plugs remain in place.
Excellent. (host clapping)
Excellent work, ladies.
And maybe the ultimate method
of cryptic female choice, the Bruce effect.
So when an already pregnant female rodent
is exposed to the scent of an unfamiliar male,
she can choose to terminate her pregnancy.
This only works before implantation in mice
but other species can terminate even a late-term pregnancy.
So the advantage of this for the female
is that they can choose the paternity of their offspring
in favour of the fittest mate.
But there are also some advantages to the males.
It allows them to sabotage the pregnancy
of a male competitor
and return the female to a fertile state more quickly.
And it maintains the male's social status
with more dominant males leaving more scent markings.
This has been an absolute adventure.
I have only scratched the surface here as I mentioned.
I've learned all of this stuff new too.
Thank you so much to Lisa.
Let me know in the comments some
of your favourite animal, mammal reproductive sex facts.
Don't forget to subscribe.
And I will see you in my next video.
Bye.
(upbeat music)