Name: Speciation
Uploaded: 2023-11-18T01:22:54.000Z
Duration: 7 min 8 s

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法助動詞 B1

So if you've seen our videos before you may know that one of us is a cat person.

Well the other one of us is a dog person, and when we were younger, we used to wonder…wouldn't

it be cool to have one animal that is half dog and half cat.

半猫半犬がいればいいのにって思ったことも

そんな子供向けテレビも見てたけど、

There was a cartoon we used to watch as a kid about that, although because of our tv

実は画像が荒くてよく見えてなかった

reception issues, it never came in very clear.

代わりに、自然の「ショー」を見てたってわけ

Hence, our childhood of instead watching nature shows.

【さっき本物みたのに、TVので泣いてる？】

As cool as a half cat, half dog animal would likely be---we need to understand that cats

さて、まずは 犬と猫は別種だってことを知らなくちゃ

同種の生物は交配できる。 そして繁殖して子孫も残せる。

Well organisms that are in the same species can interbreed AND their offspring can reproduce.

例えば、犬の品種はいっぱいあるけど 全部　同種

That means---the huge variety of domesticated dog breeds---they are all the same species.

品種が違うと　見た目は全然違うけどね

Even though they can look very different.

All the different cat breeds are STILL the same species.

「分類(classification)」動画では階層まで話すけど

You can watch our classification video to learn about the hierarchy levels in taxonomy,

この動画では、「種」に注目する

but in this video, we're just going to focus on the level of species itself.

別種が交配したら、子孫ができる？

Now can two different species breed and have offspring?

ゼブラ(シマウマ)とドンキー(ロバ)で

Yes---for example, let's consider the magnificent Zonkey.

実際にはロバとシマウマの雑種(ハイブリッド)

It's a hybrid actually---a cross between two different species---a donkey and a zebra.

They typically are going to be sterile though---so even though the donkey and the zebra had the

baby zonkey---that Zonkey will not be fertile.

Donkeys and zebras are different species so this fits into that species rule.

種分化、つまり新しい種ができる進化は

Speciation, which means the development of a new species---can occur when populations

個体群が(生殖に関して)隔離されている時に起き得る。

are reproductively isolated in some form.

見てないなら 先に「自然選択(Natural Selection)」をみて。

Well first, check out our natural selection video which talks about natural selection

進化のメカニズムと新種ができる経過を 説明してるから

as a mechanism of evolution and how change over time can lead to a new species.

さて、隔離と種の分化は どうつながるか

Our focus right now is to see how isolation can happen in the first place which can give

２つの主な種の分化について話そう

If we're going to get a little more fancy, we can talk about two main types of speciation:

異所性種分化と同所性種分化。

allopatric speciation and sympatric speciation.

And here comes our disclaimer---in our short video clip, we are only giving some examples

ホントはもっといろいろあるから！ 気になったところは調べて！

of isolation and how speciation can occur.

異所性種分化は　地理的に隔離されちゃうこと

In allopatric speciation, there is a geographic barrier that separates the populations.

自然選択下では、地理的な障壁

So while natural selection is acting on these populations, there is also some big geographical

つまり川とか山とかが、交配を阻むと

barrier---like a river, a mountain---that keeps them from being able to interbreed and

同じ遺伝子のグループが２つできる。

時が経つにつれ、それぞれはちょっと変わっていく

Eventually over a period of time there can be change over time in the separated populations

自然選択とか遺伝的浮動とかによってね

in their separated areas from mechanisms like natural selection or genetic drift.

かなり経つと、 個体群は大きく異なってしまうかも

Over time, these populations can have significant genetic differences that may not allow them

一緒にしても交配できない くらいに

to interbreed even if they were brought together.

地理的に隔離すると、別種ができる。

Populations separated geographically can form different species.

You might think you would always need a geographic boundary to separate populations, but in sympatric

同じエリアでも種分化は起きる。

speciation, the speciation happens in the same area.

Yet, there's something else isolating them.

Let's start with prezygotic barriers—that means---barriers that occur before you can

交配させない障壁って考えた方がいいかも

A zygote is a fertilized egg so a prezygotic barrier is not even allowing fertilization

グループごとに異なる行動をとること

So of these prezygotic barriers, let's start with this first one here: behavioral isolation.

非常にわずかな違いでさえも、障壁になることがある

This is when species can have different behaviors, even very slight differences, that can isolate

たとえば、鳥のさえずりがちょっと違うだけ　とか

【カントリー調(田舎くさい)・・・】

For example, birds having different songs---some only having very slight differences---can

prevent the males from attracting females of other populations.

有名な例だと、meadowlark(マキバドリ)

ニシマキバドリと　ヒガシマキバドリが　いる

何と、同じエリアに両方いることも

One of the common biology examples is the Eastern and Western meadowlark.

こいつらはそっくり でも、行動で隔離されてる

Surprisingly, you can find them in the same area.

They look SO similar…but they are isolated by their behavior.

Mates are attracted with a different song.

繁殖の季節、あるいは年だったり時間帯が違う

Temporal isolation---species could breed at different seasons, years, even different times

似ている種でも、繁殖期が違えば

They may look very similar but if they don't have the same breeding season, then you're

生育環境が同じとは限らない。

See even assuming that organisms live in the same area---that doesn't mean their habitats

例えば２種の両生類 同じとこにいても、

どっちかっていうと水が好きなのと どっちかっていうと陸が好きなのと

You could have two species of amphibians living in the general same area but if one prefers

an aquatic environment and one prefers a terrestrial environment, that will be a habitat isolation.

さて、もう一つ 接合後障壁について

Now you can have postzygotic barriers too.

交配できて、受精卵ができたとしよう

That means that mating and fertilization actually occurred because you have the zygote---a fertilized

egg---but there is some barrier that separates the species even still.

Perfect example: the offspring is not fertile.

それがロバとシマウマを分ける障壁

That's one barrier that separates donkeys and zebras.

Sometimes offspring that are produced between two different species are very weak and do

そいつは弱くって、長生きできない

交配して受精ができたとしても

And sometimes if species interbreed, the offspring is NOT able to develop in even very early

胚発生の早い段階で 雑種は発生が止まってしまうかも

embryonic stages because there is a genetic incompatibility.

All of these are postzygotic barriers that can happen in the same environment.

Now in our short video, we want to point out three things.

First, this is just a very few set of examples of isolations that can lead to speciation.

1. 動画で紹介できるのはほんの数例

We encourage you to explore the huge list of other isolation types that can lead to

だから、種分化とか隔離については

Second, species can be impacted by more than one type of isolation.

2. いくつかの隔離要因が重なって 種分化が起きてるかも １つじゃなくてね

Third, please understand that isolation itself is not the mechanism for the actual change

どう変わるかに　惑わされないで

Change over time, which can occur in gene pools of populations, can be due to mechanisms

時が経つにつれて　集団の遺伝子プールは変わるかも

遺伝的浮動とか自然淘汰によってね

For example, let's take the case of natural selection.

たとえば　自然選択が働いたら

Remember that variety naturally exists in the populations.

However, genes in a gene pool that result in high fitness---meaning more offspring---can

適応度が高い遺伝子の方が 子孫に伝わりやすい

INCREASE in the frequency of the population which can cause the population to change over

だから集団の頻度は　時間が経つと変わることもある

字幕リスト動画再生

Speciation

assume

impact

develop

variety