Hi guys! My name is Clementine! Today I am going to tell you guys how my fish friends and I came to be. Evolution can be very confusing (what is a species anyway?!) so I am here to help!

A long, long time ago fish like me didn't even exist! There was a different type of fish instead!

This fish underwent lots of selective pressures. Eventually the fish evolved into fish like me and sharks! Different selective pressures led to different organisms evolving!

You can tell that we are related to sharks because we both have fins! These fins came from our ancestor. Having the same feature is what is called a homologous structure!

Some people think that since dolphins have fins they also share a homologous feature with fish and sharks. This is not true because they evolved from different ancestors! Despite this, they still developed special features like we did.

Eventually there were fish that began to look like me!

At first some of the male fish grew red and white hooks on their forehead! Most of the females did not like the way the hook looked.

The females chose to breed with the males that did not have the hooks on their forehead! This means that the alleles for the hooks did not get passed to offspring.

Overtime, the hooks got less and less frequent. And now no one has a hook on their forehead! This is an example of sexual selection!

Now we look like normal fish with no hooks. We have three colors; red, orange, and yellow. 

Sharks are our main predator. Sharks can't see red or yellow very well so they normally eat orange fish. This means I have to be extra careful!

Over time there are less and less orange fish in our population. This is called disruptive selection! It also means that I am a rare color!

A little bit ago there was a super strong current! The current swept away some of my cousins!

Now my cousins live far away and almost all of them are red! This is called the founder effect! Because most of the fish swept away were red, most of their babies are too.

Deeper in the ocean there are other fish that live there! These have special features that let them live where it is colder and darker!

We don't see them very often and we can't interbreed because they live so far away from us in a different habitat! This is a prezygotic reproductive barrier called ecological isolation!

At home we have friends called pufferfish! They can puff up into a big ball! Even though we live in the same place as pufferfish we look a lot different. 

There most likely used to be a barrier dividing us so we evolved differently. The barrier prevented what we call gene flow. When two groups can't mate there are no longer genes being exchanged! 

Pufferfish and my species underwent allopatric speciation because we are different species that have the same ancestor but evolved in different habitats because of a barrier!

Every species acts a little different. In my species the males sometimes eat the eggs females lay!

This is because the males want to mate with the mom fish. If there are no eggs to take care of, the females can mate again! This is what we call male-male competition.

My species also has what we call direct benefits. Males help build the nest site for a female to lay her eggs. This is a direct benefit for the females! Direct benefits can affect who a female mates with.

This is sort of like when the females didn't want to mate with fish with forehead hooks! But instead it is because of resources and not looks. Females can choose which male to mate with based on how good the nest site he built is!

The red fish has a bigger nest so I'll mate with him!

The males that are better at making nesting sites breed more often so their alleles get passed on more frequently! See how there are many different things leading to sexual selection!

Now you have seen evolution from natural selection and sexual selection! The traits of fish that breed more than other fish increase in frequency over time which leads to fish like me!

Thank you for learning about evolution with me!