A Fish In This Lake Evolved Into 850 Different Species

Summary

The video delves into the remarkable biodiversity of Lake Malawi, home to over 850 species of cichlids, surpassing Europe's freshwater fish diversity. It explores the concept of adaptive radiation, where a common ancestor rapidly diversifies into many species, driven by factors like competition, habitat, and diet. The video also touches on the potential for witnessing new cichlid species formation in our lifetime, highlighting the lake's significance in evolutionary biology.

Takeaways

• 🌍 The African Great Lakes, including Lake Malawi, are home to an extraordinary biodiversity, particularly in cichlid fish species.
• 🐟 Lake Malawi alone hosts over 850 species of cichlids, which is more than the total number of freshwater fish species in all of Europe.
• 🔬 The high diversity of cichlids in Lake Malawi is attributed to a process known as adaptive radiation, where species rapidly diversify from a common ancestor.
• 💥 Competition between male cichlids, such as Metriaclima mbenji, drives the evolution of distinct coloration to reduce aggression towards similar-looking individuals.
• 🏞️ Habitat differences within Lake Malawi, which spans nearly 30,000 square kilometers, contribute to the diversification of cichlids by creating various ecological niches.
• 👀 Different cichlid species have evolved unique sensory adaptations for prey detection, such as the flavescent peacock cichlid's reliance on its lateral line system in low light conditions.
• 🍴 Diet specialization plays a significant role in cichlid diversification, with some species evolving to scrape algae, eat insects, or even feed on the scales of larger fish.
• 🦟 The cichlid Docimodus evelynae undergoes a dietary shift throughout its life, starting as a cleaner fish and eventually becoming a scale eater, illustrating the link between diet and species evolution.
• 🐢 Adaptive radiation is not exclusive to cichlids; it's also observed in other species like Darwin's finches and Anolis lizards, which have diversified in response to specific environmental pressures.
• ⏳ The short generation times of cichlids, some reaching reproductive age within 6 months to 3 years, allow for rapid speciation and the potential to witness new species formation in a human lifetime.

Q & A

What is unique about Lake Malawi in terms of its fish species?

Lake Malawi is home to over 850 species of cichlids, which is more than the total number of fish species in all of Europe's freshwater systems.

What is the significance of cichlids in Lake Malawi?

Cichlids make up around 90% of all the fish species in Lake Malawi, showcasing a high level of diversity in coloration, shape, and diet.

What is adaptive radiation, and how does it relate to the cichlids in Lake Malawi?

Adaptive radiation is the rapid increase in the number of species that share a common ancestor. It is the process that has led to the extreme diversification of cichlids in Lake Malawi.

How does competition between male cichlids contribute to their diversification?

Competition between male cichlids, such as Metriaclima mbenji, can lead to aggressive behavior towards other males, which may drive the evolution of differences in coloration to reduce conflicts.

What role does habitat play in the diversity of cichlids in Lake Malawi?

Habitat diversity within Lake Malawi, which spans almost 30,000 square kilometers, allows for various niches, leading to the evolution of cichlids adapted to different depths and light conditions.

How do the hunting preferences of cichlids like the flavescent peacock cichlid and Tramitichromis differ?

Tramitilchomis cichlids rely on their sight for prey detection, while the flavescent peacock cichlid uses its lateral line system, which is advantageous in the lower light conditions found at greater depths.

What is the relationship between diet and the diversification of cichlids in Lake Malawi?

Diet is a significant driver of adaptive radiation among cichlids, with species specializing in different food sources, such as algae scrapers, insect eaters, and even scale eaters like Docimodus evelynae.

How does the diet shift in Docimodus evelynae cichlids throughout their life stages contribute to their evolution?

The diet shift in Docimodus evelynae from eating parasites and fungus to plankton and eventually scales of larger fish, along with changes in their teeth, has led to the evolution of distinct physical characteristics that may contribute to speciation.

Why are short generation times of cichlids significant for adaptive radiation?

Cichlids can reach reproductive age in as little as 6 months to 3 years, allowing for rapid passing down of traits and potentially leading to the formation of new species within a human lifetime.

How do lakes and islands facilitate rapid speciation, as seen in Lake Malawi and the Galapagos finches?

Lakes and islands provide limited competition and a plethora of available niches for ancestral species to fill, leading to rapid speciation and diversification, as observed in cichlids in Lake Malawi and finches in the Galapagos.

What other examples of adaptive radiation are mentioned in the script?

The script mentions Darwin's Galapagos finches, which show diversity in beak size and shape, and Anolis lizards in the Caribbean, which have diversified to occupy various ecological niches.

Outlines

00:00

🐟 Lake Malawi's Cichlid Diversity

The video script introduces the African Great Lakes, specifically Lake Malawi, which is home to over 850 species of cichlids, a single type of fish. This high diversity is more than the total number of fish species found in all of Europe's freshwater systems. The script discusses the concept of adaptive radiation, which is the rapid increase in species that share a common ancestor. Factors contributing to this diversity include competition between male cichlids, habitat differences within the lake, and various dietary preferences. The script also mentions the short generation times of cichlids, which allows for rapid speciation, and draws parallels to Darwin's finches and Anolis lizards as other examples of adaptive radiation.

05:01

🌿 The Drivers of Adaptive Radiation in Cichlids

This section delves deeper into the factors that drive adaptive radiation in cichlids. It explains how competition and habitat play significant roles in the diversification of cichlids in Lake Malawi. The script uses examples such as Metriaclima mbenji, which exhibits aggressive behavior towards other males, and the different hunting preferences of the flavescent peacock cichlid and Tramitichromis. It also discusses how diet specialization, such as algae scraping and scale eating, contributes to the evolution of new species. The video emphasizes the rapid generation times of cichlids, which allows for quick passing down of traits and the potential to witness new species formation in our lifetime. The script concludes by highlighting the importance of lakes and islands as settings for rapid speciation due to limited competition and the abundance of available niches.

Keywords

💡Great Lakes

The Great Lakes are a series of large freshwater lakes primarily in the northeastern part of North America. In the context of the video, the term is first used to refer to the well-known Great Lakes in the US and Canada but then shifts to highlight the lesser-known African Great Lakes, such as Lake Malawi, which is the focal point of the video's discussion on biodiversity.

💡Lake Malawi

Lake Malawi, also known as Lake Nyasa, is a large freshwater lake in southeastern Africa. The video focuses on this lake because it hosts an extraordinary biodiversity of fish, particularly cichlids, making it a significant area of study for evolutionary biologists interested in adaptive radiation.

💡Cichlids

Cichlids are a family of freshwater fish known for their diversity in coloration, shape, and diet. The video emphasizes that Lake Malawi is home to over 850 species of cichlids, which account for approximately 90% of the fish species in the lake, showcasing an example of adaptive radiation.

💡Adaptive Radiation

Adaptive radiation refers to the rapid diversification of a group of organisms into multiple new species, often in response to new ecological niches. The video explains how adaptive radiation has led to the vast number of cichlid species in Lake Malawi, as they evolved to exploit different habitats and resources within the lake.

💡Competition

Competition among male cichlids for territory and mates is highlighted as a driver of adaptive radiation in the video. The example of Metriaclima mbenji illustrates how aggressive behavior can lead to the evolution of distinct species to reduce conflict, as they evolve to look different from one another.

💡Habitat

Habitat diversity within Lake Malawi is discussed as a significant factor contributing to the lake's high biodiversity. The video mentions how different cichlid species have adapted to various depths and light conditions within the lake, leading to the evolution of distinct species.

💡Prey Detection

Prey detection abilities are used to illustrate how cichlids have adapted to their environments. The video contrasts the sight-based detection of Tramitichromis cichlids with the lateral line system used by the flavescent peacock cichlid, showing how these adaptations allow them to thrive in different depths of the lake.

💡Diet Specialization

The video discusses how diet specialization has contributed to the diversification of cichlids in Lake Malawi. It gives the example of the scale-eating cichlid Docimodus evelynae, which changes its diet as it grows, leading to the evolution of specialized teeth and potentially new species.

💡Generation Times

Generation times refer to the time it takes for an organism to reach reproductive maturity and produce offspring. The video explains that cichlids have short generation times, which allows for rapid evolution and the potential for new species to emerge within a human lifetime.

💡Evolutionary Biologists

Evolutionary biologists are scientists who study the processes that lead to the diversity of life on Earth. The video mentions that Lake Malawi is a hot topic among these biologists due to the high number of cichlid species and the opportunity to study adaptive radiation in action.

💡Niche

A niche refers to the specific role or position an organism occupies in its environment, including its habitat, behavior, and the way it obtains food. The video explains how the vast size of Lake Malawi provides numerous niches for cichlids to occupy, leading to a high degree of specialization and diversity.

Highlights

Lake Malawi contains more than 850 species of cichlids, a unique example of adaptive radiation.

Cichlids make up 90% of all the fish species in Lake Malawi, showing extraordinary diversity.

The process of adaptive radiation explains the rapid increase in species diversity from a common ancestor.

Competition between male cichlids, like the Metriaclima mbenji, drives color differences to avoid conflict.

Lake Malawi's massive size (30,000 square kilometers) provides various habitats for diverse cichlid species.

Cichlids like the Tramitichromis and the flavescent peacock differ in prey detection methods due to their habitats.

The flavescent peacock cichlid uses its lateral line system to detect prey in lower light levels, aiding its survival in deep waters.

Habitat depth influences evolution; for instance, flavescent peacock cichlids can live up to 120 meters deep, unlike their shallow-water counterparts.

Cichlid diet specialization, such as feeding on algae, insects, or fish scales, contributes to species diversity.

Species like Docimodus evelynae undergo a diet shift, starting as parasite eaters and evolving into scale eaters as they grow.

Cichlid species have short generation times (6 months to 3 years), accelerating the pace of evolutionary diversification.

Scientists believe new species of cichlids could form within our lifetime due to their rapid adaptive radiation.

Adaptive radiation is not unique to cichlids; Darwin's finches in the Galapagos and Anolis lizards in the Caribbean are other examples.

Lakes and islands, like Lake Malawi and the Galapagos Islands, provide ideal conditions for rapid speciation due to limited competition.

Cichlids exhibit rapid diversification globally, including in places like the Amazon, making them highly successful in speciation.

Transcripts

Have you heard of the Great Lakes?

No, not the ones in the US and Canada!

Though Lake Michigan does happen  to be one of my favorites.

I’m talking about the African Great lakes!  Lake Edward, Lake Kivu … Lake Malawi.

Well, there’s something really  weird happening in that last one.

This lake has more than 850  species of ONE type of fish.

That’s more than the total  number of species of fish

in all of Europe's freshwater systems.

So, what the heck is going on in Lake Malawi?!

[♪ INTRO]

Not long after Charles Darwin  made it to the Galapagos Islands

and began studying the famously diverse  finches there, news arrived in Europe

that a massive body of water had been  discovered in southeastern Africa.

Of course, the people who  had been living there had

known about it for centuries. But  that’s a subject for another video.

Anyway, it would come to be known as Lake Malawi.

Today, the lake is a hot topic of  conversation among evolutionary biologists.

Why? Because it has more than  850 species of just cichlids!

Cichlids make up around 90% of all  the fish that exist in the lake!

If you have an aquarium, you’re  probably familiar with cichlids.

There’s diversity galore in the coloration,  shape, and the diet of these vibrant fish.

Lake Malawi really has the original DEI:

Diversity, evolution, and  ichthyology, the study of fish.

But why do we see so much  diversity in this one lake?

The reason is a process called adaptive radiation.

It’s the rapid increase in the number  of species that share a common ancestor.

Which is great. We have a definition.

But what would provoke such an  extreme diversification of these fish?

One cause is competition between male cichlids.

Metriaclima mbenji is a beautifully  colored speckled cichlid that

has some aggressive tendencies,  specifically towards other male cichlids.

When given their own territory, you can  bet they’ll make an effort to protect it!

When an mbenjii male is forced  to defend his territory,

studies have shown that he'll do  so more aggressively against males

of his own species and males of  other species that look like him.

So there's some incentive to  evolve differences in coloration

so that cichlids that look like  you aren’t constantly attacking.

Another driver of cichlid diversity  in Lake Malawi is habitat.

Which seems weird considering  they live in the same lake!

But this lake is a whopper—almost  30,000 square kilometers.

Plenty of room for several  different types of habitats.

For example, one study focused  on the hunting preferences of

two different benthic, or  bottom dwelling, cichlids:

the flavescent peacock cichlid and a  species from the genus Tramitichromis.

Tramitichromis cichlids tend to  use their sight for prey detection.

The flavescent peacock, on the other  hand, often uses its lateral line system.

That’s an extra sense that fish have  along the sides of their body that

helps them detect movement in the water.

It’s also a sense I very much wish I had.

When assessing the prey detection  abilities of these two species in

varying levels of light, scientists found  that our flavescent friend was able to

detect more prey at lower light  levels than Tramitichromis.

When you think about their  habitat, that makes perfect sense!

Tramitichromis lives in shallower  waters, typically less than 15 m deep,

whereas the flavescent peacock can  live as deep as 120 meters down,

in an environment where light levels are much

lower than what Tramitichromis is used to.

So, the need to detect prey better  in lower light may have driven

the evolution of a new species that  could operate at greater depths.

It seems as though this town is, in  fact, big enough for the two of them.

Thanks to Incogni for supporting this  SciShow video! Incogni is here to

help you stay away from cybercrime  and personal privacy breaches.

Data brokers collect and sell personal  information, including Social Security

numbers, login credentials, home  addresses, location history, and more.

And having your personal  information on so many databases

puts you at an increased risk of cybercrime.

You could end up with spam  from the marketing agencies

they sell your info to and  more serious identity theft.

And that’s what Incogni steps in to prevent.

They reach out to data brokers  on your behalf and request

that they remove your personal data.

And if a new record pops up, they’ll  automatically take care of it.

So you’re covered for as  long as you use the service.

You can also use the Family & Friends  plan to add up to four members

to your subscription so they benefit  from the same exact service you do.

Anyone can try it out for 30  days and get a full refund

if you aren’t happy with the service.

So to take your personal data back  with Incogni, use the code SciShow at

incogni.com/scishow or the link in the  description and get 60% off an annual plan.

Competition and habitat aren’t the  only drivers of adaptive radiation.

Diet is another huge one.

There are cichlids that specialize  in scraping algae off rocks,

and others that prefer insects.

There are even cichlids that feast  on the scales of larger fish!

One kind of scale eating  cichlid, Docimodus evelynae,

goes through a diet shift as it gets older.

It starts out more like a cleaner  fish, eating parasites and fungus.

As it grows larger and its teeth  start to change, so does its diet.

It begins eating plankton when it’s  available during its adolescence.

Finally, once it reaches its larger sizes,  it has lost all its baby teeth and has

gained bigger, pointer ones,  perfect for plucking chunks of

skin and scales right off of larger fish.

Picking on someone bigger than you may  seem like a precarious way to live,

but it seems to have worked  for a few cichlid species!

This specialization seems  to have led to the evolution

of a distinct set of teeth to match that diet.

It’s the kind of thing that, over  time, can lead to a new species!

These drivers of diversity can  work especially fast in cichlids,

since their generation times are so short.

Think of it this way: lots of organisms,  like us, have long generation times.

Passing down traits to your offspring won’t  lead to the formation of a new species

very quickly if you’re only passing  them down every 20-30 years.

But some cichlids reach reproductive  age at 6 months to 3 years old.

And with so many aspects of their lives,  like habitat, behavior, ecology, etc.,

being so different, there’s a lot of  diversity to pass down very quickly.

Some scientists suggest we may get  a new species or two of cichlids

in this lifetime, meaning  we’ll be able to watch the

formation of a new species  occur right before our eyes!

And adaptive radiation is happening  in more than just cichlids.

One of the most well known  examples is Darwin’s famous

Galapagos finches I mentioned earlier.

They show incredible diversity between islands,

namely in their beak size and shape.

This allows the different  species to specialize on whatever

food is available on their island.

This was one of the observations that  inspired Darwin’s theory of evolution.

Anolis lizards in the Caribbean  are another great example!

The lizards took over different  niches all over the Caribbean islands,

from the ground, to the bushes, to  the trunks and tops of the trees.

And now there are about 150 species of them.

So it has happened in other  places… but why Lake Malawi?

Well, lakes and islands are the  perfect setting for rapid speciation.

Notice how the two other  examples I named were on islands?

In such places, competition with  other types of organisms is limited.

Once the ancestral species  arrives, there are usually tons of

niches available for them to fill.

They’d have a field day with  all those opportunities!

And like I said before, Lake Malawi is massive.

With all that water, there’s  a lot of space for a lot of

different niches and a lot of diversity!

But if another type of fish got to  Lake Malawi before the cichlids,

would they have radiated the same way?

Cichlids are wildly diverse in Lake Malawi.

But they’re also diverse  across the world in the Amazon.

Clearly they’ve got this  whole speciation thing down.

With fish that seem to diversify  quickly and a lake with enough space

for the fish to do their  thing, Lake Malawi and cichlids

seem to be the dream team in  the game of adaptive radiation.

[♪ OUTRO]