Almost every animal species on the planet has sex. But perhaps no creature shows as much commitment
to their reproductive craft as antechinuses. The small marsupials are indigenous to Australia,
and every summer the continent basically turns into antechinus Love Island—by which I mean
“a short period of nonstop sexual couplings devoid of anything resembling human emotion.”
The physical toll of this weeks-long mate-a-thon
is a 100 percent mortality rate amongst several species of male antechinuses, leading some sources
to dub the phenomenon “mating to death.”
Today we’re discussing some of the strangest facts about sex in the animal kingdom
(non-human division), from the details of this critter-killing copulation to the beautiful
“bladder songs” of haddock. If nothing else, I can promise that you will never look at an alligator
the same way again. Let’s get started.
During mating season, each male antechinus seeks out as many female partners as possible
in an effort to pass on his genes. It can be extremely exhausting work—a single
mating session can last up to 14 hours. The dramatic influx of hormones and the stress
of the grueling schedule wreak havoc on the poor little guys’ bodies. Internal bleeding,
hair loss, and blindness are just some of the common consequences. Still, these single-minded
marsupials doggedly pursue their reproductive goals. As the University of Queensland’s Diana
Fisher told National Geographic, “By the end of the mating season, physically disintegrating males
may run around frantically searching for last mating opportunities.” I think I saw a similar
phenomenon play out at an off-campus bar during undergrad, but at least the males there were not,
to my knowledge, riddled with gangrene.
Experts differ on why these animals have evolved to be semelparous, breeding just once in their
lifetime. It’s a fairly common trait amongst certain types of animals, but that usually
doesn’t include mammals. Dr. Fisher thinks it could be related to antechinuses’ diet.
They subsist on insects, and unfortunately they can’t go to the Insect-Mart to stock up every week
(although it would be objectively adorable if they could). Instead,
they may have evolved to make the best use of annual swells in food availability,
giving birth in a narrow range of time when mothers would be best-fed and able to support
their young. That tight timeframe creates a lot of pressure on males to make hay while the sun
shines. … Or, you know, to make marsupial love while they’ve still got at least one working
eyeball.
For mangrove killifish, mating is less dangerous, but maybe a bit lonelier.
Most of them are hermaphrodites, and can actually sexually reproduce with themselves—a process
which, as Sarah Jane Alger wrote for Nature’s Scitable, is, “amusingly enough, called selfing.”
That’s kinda cool, but it’s not particularly strange: hundreds of fish species exhibit some
form of hermaphroditism; it actually occurs in about one-third of non-insect animal species.
But not all killifish reproduce through selfing. A small but significant percentage of the species
has male-only sex organs, while there seem to be no reproductive females. Even though one
hermaphroditic killifish could theoretically mate with another, in practice that doesn’t happen.
It all leads to a situation that reminds me of those logic problems where Janey goes to a picnic
and can sit next to anyone but Johnny; Johnny can sit next to anyone who didn’t bring deviled eggs;
and somehow I end up with a messy grid that says Johnny brought caviar and also cannot logically
exist.
Hermaphroditic killifish can reproduce with themselves or with males, but seemingly not with
other hermaphrodites; males can only reproduce with hermaphrodites. The impact of this sexual
arrangement and killifish demographics is that hermaphroditic individuals will mate
with basically any male, regardless of whether or not they are closely related to that particular
male. The males, in contrast, can afford to be more picky—tending to avoid closely-related
hermaphrodites they encounter in an apparent attempt to maximize genetic diversity. Suddenly
selfing is starting to seem a lot simpler.
Sea slugs also commonly exhibit hermaphroditism, and they get even more creative with their sexual
couplings. In some species, about half of sexual encounters are considered “reciprocal matings,”
where both individuals simultaneously act as male and female. Whatever you’re
picturing in your head right now, I can assure you that the reality is gnarlier.
Each slug basically harpoons
the other with a “penile appendage terminating in a syringe-shaped stylet to extragenitally
inject prostate fluids into their partner,” in the not-exactly-Harlequin-Romance-level language
of a team of German researchers. Each penis has hook-shaped spines on it “which are spread like an
anchor in the female genital tract during mating,” or, in this case, in both partners simultaneously.
It can all make for some contentious encounters, but the reciprocal matings can theoretically
increase the chance of reproductive success.
One other hermaphroditic species, the flatworm, sometimes decides who gives or receives sperm
a bit more aggressively. Some species inseminate their partners by injecting sperm directly into
the surface of their skin. This process, called “hypodermic insemination,” is decided with an
epic battle known as “penis fencing.” This is exactly what it sounds like—the
two flatworms compete in a phallic jousting match lasting as long as an hour. Eventually, one lands
the first hit, fertilizing the other’s eggs. The consolation prize for the loser? Motherhood.
Thanks to YouTube commenter Velata for bringing up penis fencing in our video about the deadliest
toys ever made. We’ve got an upcoming episode all about facts that will make you reassess
time. (Things like the fact that Cleopatra lived closer to the present day than the time when the
Great Pyramids were built.) If you’ve got a good example, drop it in the comments below for a
chance to be featured in that episode.
We’ve mostly talked about animals actually doing the deed, but sometimes the lead-up to
sex can be as fascinating as the actual act of reproduction. For male haddock, this involves a
unique mating call.
Sidenote: I was going to segue into haddock by saying that fish, of course, can’t sing like
birds, but turns out that’s not quite right. Apparently some species of fish engage in what
amounts to underwater shouting matches. Fish communities off the coast of Australia were
documented singing … “seven distinct choruses, which rise up at both dawn and at dusk,” according
to Science Alert. And as The New Yorker noted in an image caption on a piece by Emily Anthis,
“more than eight hundred fish species are known to hoot, moan, grunt, groan, thump,
bark, or otherwise vocalize.”
In the case of haddock, a percussive tremolo is produced by muscles attached to their swim
bladders. The sounds become “ … longer and faster as the level of arousal of the male
increases,” according to a paper published in the Environmental Biology of Fishes.
Male ducks have corkscrew-shaped
penises that, when not mating, rest in a sack on their bodies. They don’t become erect until
after mounting. When the duck finds a mate, it mounts the female and turns its penis inside
out to enter her body. The penis enlarges to a quarter of the duck’s total body length—about
20 centimeters, on average. The record for penis length in ducks belongs to an Argentine lake duck,
clocking in at 42.5 centimeters, or nearly 17 inches. Just in case you were wondering.
Unfortunately, many instances of
duck sex are non-consensual on the female’s end. Luckily, female ducks have a built-in self defense
mechanism. Duck vaginas are also corkscrew shaped, twisting in the opposite direction
of their phallic counterparts. To prevent itself from getting cork-screwed over into an unwanted
pregnancy, the hen uses its vagina to limit how far the male’s penis can travel, and subsequently
how far up the vaginal cavity ejaculate can travel. Discover magazine dubbed this unique bit
of duck anatomy “organic chastity belts.”
Most birds, male or female, don’t have penises at all—over 95 percent of all bird species lack
the appendages, in fact, including eagles and penguins. Instead, males and females briefly
press their genital openings, known as cloacas, against one another in a move that’s been called
a “cloacal kiss.”
Female argonaut octopuses can weigh as much as 600 times their male counterparts, but those
little guys display some big-time creativity when it comes to mating. During copulation,
males insert a special arm called a hectocotylus into the females. “ … [T]hat reproductive arm is
used to transfer the sperm inside the female,” as marine biologist James Wood told Wired in 2015.
Despite that important function, males aren’t very attached to their hectocotyli. They actually leave
the arms behind when they swim away.
Giant pandas are known for their low breeding levels. It’s not that they’re not naturally down
to clown—in fact, wild pandas show no evidence of trouble breeding in their natural habitats.
Since pandas in reserves are usually separated by sex until it’s time to mate,
they simply don’t know how to flirt. It doesn’t help that male pandas have among the smallest
penises in the animal kingdom in proportion to body size. An adult male panda’s penis is only
three centimeters long, and in this case, size does matter—it makes successful reproduction less
likely. To make matters worse, mating occurs only a handful of days per year due to the female’s
ovulation cycle.
Burrowing barnacles, in contrast, have the (proportionally) largest penises,
which can be up to nine times the length of their bodies. Since burrowing barnacles can’t
move around easily, they whip their penises out in hopes that it bumps up against a nearby female.
And on the subject of size,
you may be surprised to learn that mouse sperm is actually longer than elephant sperm—not
just proportionally to the animals, but in absolute terms. Even then, the male deer mouse’s
relatively large swimmers will group together to improve the likelihood of fertilizing an
egg. Apparently a group of about seven sperm is the sweet-spot to limit competition but enhance
the ability to reach their destination. File that away for your next game of bar trivia.
Alligators have permanently erect penises. That’s
not to suggest they’re constantly filled with blood—they’re actually made from collagen, a stiff
protein. And though they don’t exactly “whip” them around like a barnacle, the best guess is that
they “[shoot] out like toothpaste from a tube,” in the evocative words of Ed Yong, writing for
National Geographic, before bouncing back as if it were attached to a rubber band. … If, ya know, a
rubber band could get a female alligator pregnant.
If your pet cat has ever licked you, you probably experienced a rough, sandpaper-y sensation. This
is due to cats’ tongues having hard, tiny spines called papillae, which also happen
to be found on the male’s penis. These spines are thought to help trigger ovulation. After mating,
a cat’s penis, spines and all, retracts back into the foreskin. Yeah, they have those too.
North American porcupines are known to put the
“pee” in foreplay. The female expels urine, along with other odorous vaginal secretions, in the same
way that Kelis uses her milkshake—to bring all the boys to the yard. The male porcupines that show up
fight for her honor. The winner sits at a low tree branch and uses his pee to gauge whether
or not the female is interested. Porcupine expert and author of The North American Porcupine Uldis
Roze describes this victorious ejaculation as "a high-speed projectile that launches drops of urine
from one tree branch to another." If the female isn’t into it for some… shocking reason, she’ll
bite or yell at the male until he takes the hint.
Urine also plays a role in giraffe mating. Males will smell and even taste a female’s urine in
order to determine if she’s in heat.
Hippopotamuses, on the other hand, don’t limit themselves to one form of seduction secretion.
Males will poop, pee, and fart near potential mates to attract attention. They even
spin their tails around to make sure the irresistible aromas waft out in all directions.
To show that the feeling is reciprocated, an interested female will “[shower] him in dung.”
During
their mating season, some horseshoe crabs flock to beach shorelines by the tens of
thousands for a month-long orgy. According to marine biologist Martin Schreibman,
group sex is typical among the horseshoe crab population. He says: “The more males there are
attempting to fertilize a female that is laying 80,000 eggs in a season, the better the odds
the eggs will be fertilized.” And the odds have proven effective. With such successful group sex,
it’s no surprise that horseshoe crabs have been around for over 445 million years.
Bonobos also engage in group sex,
although their orgies are likely more for pleasure than for procreation. According to
National Geographic, “Studies suggest 75 percent of bonobo sex is nonreproductive and that nearly
all bonobos are bisexual.” Seeing as humans share 98 percent or more of our DNA with bonobos,
it probably shouldn’t be too surprising that we have some overlapping sexual habits. In addition
to developing casual sexual relationships, bonobos frequently kiss during intercourse,
and even engage in foreplay and oral sex. Out of all the sexual behaviors
discussed in this video, I’m glad humans take more after bonobos than antechinuses.
Thanks for watching The List Show.
If we left out a great fact about animal sex, drop it in the comments below. We’ll see you next time!