Name: これらの7つの種のために、セックスはすべてを変える (For These 7 Species, Sex Changes Everything)
Uploaded: 2021-01-14T10:28:50.000Z
Duration: 11 min 48 s
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Animals and plants come in an amazing variety of shapes, sizes and colors.

And generally speaking, biologists can use these traits to sort out different species.

But sometimes, members of the same species look vastly different.

Like, some are way bigger, have totally different colors, or even live as parasites on others

— yes, I'm looking at you, male anglerfish.

In fact, this often happens with sexes, because having different gonads can mean individuals

When differences occur between sexes — other than their reproductive parts, of course — biologists

One of the most obvious ways that sexes can differ is their size.

In our species, for example, people who produce sperm are, on average, a bit larger.

But we've got nothing on Southern Elephant Seals.

Males of this species are between four and 10 times heavier than females.

And it's not that male seals are getting their workouts in more often.

Their size is the result of sexual selection.

That's when the traits that give individuals an advantage over others are solely related

And it often happens in mating systems like the elephant seal's, where one male breeds

with many females, because most males end up partnerless.

Only the males on the extreme end of the key traits that let them win against other males

And then their extreme genes get passed to the next generation.

Over time, these traits can get exaggerated to the point of absurdity, a phenomenon scientists

Males control harems of females that they breed with, and harem leaders are decided

So, they're usually the heaviest seals around, since their size helps them overpower the

And their victories in battle score them fatherhood of almost 90% of all elephant seal pups.

Though, there's a species of cichlid from Africa's Lake Tanganyika that's even more

In these fish, males are sometimes 12 times heavier than females.

But it's not because they duke it out over mates.

Male cichlids compete for females by hauling and defending impressively large snail shells

And after mating, the females go inside the shells to spawn and look after their brood.

That means there are selective pressures related to size for both sexes, and that's why they're

Not only is there pressure for males to be buff, there's also pressure for females

to be dainty so they fit into the shells.

Now, a lot of sexually dimorphic traits exist because males of that species compete for

the attention of females — which might seem a bit unfair.

Like, girls can fight over awesome guys, too, Nature.

But, males are often the ones competing for mates because females sink a lot of energy

into making egg cells, which are orders of magnitude larger than the males' sperm.

And this imbalance in investment can also lead to what used to be called reverse sexual

dimorphism: where females are bigger than their partners.

Though, that makes it sound like it's rare or something, and it's not.

Just look at pretty much any insect or spider, lots of fish, and most reptiles.

But it's rarer in terrestrial mammals and birds — which is why the large female moas

that dominated New Zealand until about 500 years ago stand out.

In these giant flightless birds, females were sometimes nearly 7 times heavier than males!

Females of the largest species weighed as much as 240 kilograms, while their mates were

That's probably because it took a female moa about a decade to reach the age where

So when a female did eventually have a chick, she really wanted to make sure it survived.

And unlike with other birds, she didn't have to stay dainty to take to the skies.

So, the larger her body was, the more energy she could store, and therefore, the more she

Females are often understandably choosy about who they let fertilize their expensive eggs.

And for the most part, if males want to pass on their genes, they have to impress a female

For elephant seals, that means being king of the sand.

But for many birds, it means looking absolutely fabulous.

Compare a male Mandarin duck to a female one, for example, and you'll see what I mean.

And beautiful male colors aren't just for show.

Often, they tell females if a male has good genes or will be a good dad.

In other words, they're honest signals of mate quality.

Females — who have relatively dull feathers — go for males with bright yellow and blue

feathers and more ultraviolet sheen to their tails.

And that's probably because those colorful males produce hardier kids.

A 1993 study published in Nature showed that brightly-colored male chicks — who got their

color from their dad — lived longer than duller male chicks, even if they were raised

So if a great tit has a bright splendid plumage, it indicates he'll pass on some awesome

See, some of a male's color comes from his diet.

And a 2001 study found that chicks raised by brighter males grew bigger than chicks

raised by dull males, regardless of whether their biological father was bright or not.

So those bright colors also tell females that he's good at finding nutritious food for

Sexual dimorphism is often talked about as an animal thing, but some plants separate

their sexes, too — probably because keeping them apart can help prevent inbreeding.

Unlike other orchids, where flowers have both male and female parts, catasetum plants make

Male flowers are bright, ornate, and have petals that flare out in a star shape, whereas

female flowers are usually green, subdued, and hooded.

And having such different-looking flowers helps promote their pollination by bees.

See, they're pollinated exclusively by euglossine bees that seek out the orchids' flowery

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これらの7つの種のために、セックスはすべてを変える (For These 7 Species, Sex Changes Everything)

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