Name: カブトムシが多いのはなぜ？ (Why Are There So Many Beetles?)
Uploaded: 2021-01-14T10:30:20.000Z
Duration: 6 min 11 s
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Thanks to Brilliant for supporting this episode of Scishow.

Go to Brilliant.org/scishow to learn more.

We're talking somewhere around 400,000 individual species — from weird-looking weevils to

They're the most diverse group of complex organisms on Earth, and they make up over

That's right. One in five species on this planet is...a beetle.

For a single group to be that massive, there must be an explanation.

They've been around a long time, but so have crocodiles and there's only like 20

One established idea comes from a report published in Science back in 1998.

It suggests that beetles get their diversity thanks to a relationship they formed way back

in the Cretaceous period with a brand-new food source — flowering

Even though flowering plants are common today, they're actually newcomers in terms of evolution.

They first appeared around 130 million years ago, during the early Cretaceous.

Now, they weren't responsible for the original evolution of beetles;

the first beetles evolved way further back. But flowers did give them a huge opportunity.

For millions of years, non-flowering plants like conifers and cycads had been the dominant

but about 125 million years ago there was a huge shift in the plant world as flowers

The flower takeover was probably a rough time for animals

that had adapted to the way things were, but beetles may have had a special advantage.

For instance, they may have been some of the first flower pollinators,

since they'd already been busy pollinating those older plant species.

And bees and butterflies weren't around yet to compete with them.

But beetles also probably ate these new plants.

flowering plants would have opened tons of new niches

and likely supported a huge burst of diversification.

This idea was based on a scientific technique called phylogenetic analysis.

It's a technique scientists use to estimate evolutionary relationships

by comparing the traits or genetic sequences of a group of organisms.

This can help reveal things like how closely two species are related,

where certain traits were gained or lost,

But even though this analysis shows a connection between the rise of flowering plants

there are still questions— like just how closely these events actually

lined up, or why beetles, of all things, could take

And it seems like there may be more to the story.

A new analysis from 2019 hints that the beetles got a helping hand

from a new set of digestive enzymes, which made it easier for them to digest this

The authors of the study were trying to figure out when and how

beetles got certain enzymes that let them digest tough, complex compounds

found in plant cell walls, like cellulose.

The research was also based on phylogeny,

the scientists think that these digestive enzyme genes

around the same time flowering plants evolved.

This may help explain why beetles were able to thrive

alongside flowering plants when they took over:

they would have been able to digest these new food sources

and take advantage of completely new niches,

But what's really cool is where these enzymes came from.

Because the fact that beetles make enzymes

specifically for digesting cellulose is pretty unusual.

Other animals, like termites, generally count on microbes

But, in many cases, beetles have the instructions

for these digestive enzymes in their own genome.

These special genes look like they're the result of horizontal gene transfer

— a strange thing that happens where genetic material from one species

gets into the genome of another species, sometimes through a virus.

The scientists think the genes for these super-digesting enzymes

may have started out in some ancient bacteria or fungus

That tells us that beetle diversity probably comes down to

a combination of factors—partly their evolution

alongside flowers, and partly these super-digesting enzymes.

But there may be one more thing beetles have going for them

— that's the fact that they tend to not go extinct...

A 2007 analysis looked at the largest group of beetle species,

which includes families like scarab beetles and stag beetles,

and it found that they seem really good at avoiding extinction.

Many families may even have weathered the event

either to competitors or changing environments.

But beetle families seem to be able to roll with the changes.

Research focused on the last 25 million years

suggests they're mobile enough to change their home ranges

And the fact that they're so good at fitting into

different niches might help them survive as a whole.

While certain species might get out-competed or die out

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カブトムシが多いのはなぜ？ (Why Are There So Many Beetles?)

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