Why are Guppies so Diverse?

Guppies (Poecilia reticulata) are a type of fish that you can see in just about every pet store. If you went swimming in a freshwater stream near the Equator, you may see guppies there too. You can even see guppies living in the sewers of Rio de Janeiro, Brazil! Guppies are popular as pets because they come in many different colours and patterns. 

Did you know? 

Guppies are also known as millionfish and rainbow fish.

But even though all of these guppies are the same species of fish, they may look and behave very differently. This diversity makes them very interesting for scientists to study. Ecologists call the way an organism looks and behaves its traits. 

For example, look at all of the different shapes of guppy fins and tails.

Some guppies have round tails. Some guppies have tails shaped like fans or flags. Some guppies even have tails shaped like swords!

Guppies also come in many colours. For example, their bodies might be silver or blue. Their tails might be yellow, pink, orange or several different colours!

Let’s look at why guppies can have very different traits.

Do male and female guppies look the same? 

In many types of animals, males and females of a species do not look the same. Males can often be more showy than females. This is so that they can attract mates. Females tend to be drab. This is so that they can hide better. They hide to keep themselves and their young safe. 

Male and female guppies do not look the same. Male guppies are more colourful than female guppies. Can you tell the difference between male guppies and female guppies in the pictures below? 

Female guppies prefer to mate with the showiest male guppies they can find. But many guppies get eaten by predators.  If a showy male can survive, then it is probably a good choice for a mate.

How do guppy traits help them adapt to their environment?

Guppies live in a lot of different environments. In each environment, they need specific traits to survive. Scientists call the development of these specific traits a local adaptation. A species will adapt to its environment in a way that will let it survive there.

For example, some guppies live in the same streams as the animals that eat them. These animals are called their predators. Other guppies do not live in the same streams as their predators. Ecologists have found that these two types of guppies have different traits.

One type of guppy predator is a fish called the cichlid.

Did you know? 

Some cichlids are very good predators. They have long, thin bodies that let them swim quickly. They also have strong jaws that let them catch a lot of prey. 

The guppies that live in the same streams as cichlids tend to have drab colours. This helps them camouflage. These fish have a better chance of not being eaten by cichlids. 

Let’s look at those guppy photos one more time.

The pictures on the left are wild guppies. The pictures on the right are pet store guppies. Do you notice how wild guppies are not very colourful?

Do guppies in different places have different reproductive strategies?

Guppy young are called fry. The guppies that live in the same streams as cichlids start to reproduce at a very young age. They have lots of fry. This way, there is a greater chance that at least some of those fry will survive to adulthood.  

The guppies that live in streams without cichlids tend to be much brighter. Since they do not have to worry about being seen by cichlids, they can be very bright and flashy. (Remember, females prefer flashy males!) The females do not have to rush to mate. They also have fewer, larger fry. These fry have a good chance of surviving. 

Do the same things happen with pet guppies?

Yes! Guppies raised to be pets live in tanks without predators. Females are free to choose the males they like best. As you now know, these are the most colourful ones. People who want to breed guppies will often look for males and females of interesting colours and shapes. When they mate, guppies of new and interesting colours and shapes are born!

So the next time you are in a pet store, check out the guppies. Think about why they look the way they do. Try to spot the males and the females. And maybe you’ll even bring one home!