Amphibian Reproduction

Instructor: Danielle Haak

Danielle has a PhD in Natural Resource Sciences and a MSc in Biological Sciences

Amphibians are organisms that spend part of their lives developing in water before they're able to live on both land and in water. This unique ecological characteristic means they have a different reproductive strategy than humans.

What Is an Amphibian?

An amphibian is an animal that starts its life living in water. At this stage, it breathes through gills and has a tail. Once it matures, it develops lungs to breathe and legs to walk on, enabling it to go back and forth between water and land.

We can divide amphibians up into four different categories: salamanders and newts, toads, frogs, and caecilians. Generally speaking, amphibians usually lay a lot of eggs to increase the probability that at least some will survive. Most amphibians leaves their eggs after fertilization and are not involved with offspring any further. Each group's reproductive strategy is similar, yet there are slight differences, so let's take a look at each.

Salamanders and Newts

Salamanders and newts usually reproduce during the winter months. They use a type of internal fertilization that does not require sexual intercourse. This might sound puzzling, but let me explain what happens. When a male is ready to mate, he will look for a female. When he finds one, he gets close to her and uses his tail to waft glandular secretions (like pheromones) in her direction. This signals her to approach him (assuming she is also ready to mate).

Once she's next to him, he will deposit a spermatophore next to her. This is a packet of sperm she can use to fertilize her eggs. To do this, she inserts the spermatophore into her body through her cloaca. A cloaca is an opening to the body where the intestinal, urinary, and reproductive tracts all have their exits (or entry as the case may be). Her eggs are fertilized inside her body and then deposited outside and covered with a gelatinous membrane for protection (amphibian eggs do not have shells; they have to be laid in water so they don't dry out during incubation).

Some species hatch outside the female, but others remain inside the female from 3 weeks to 2 years!

Longtailed Salamander
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Toads

Males call out to females by croaking, so every time you hear a toad (or frog) calling, you are really hearing them signal to potential mates that they are ready to reproduce! Once a male and female come together, they use the amplexus position to fertilize the eggs. The male grasps the female until he releases sperm at the same time she releases eggs. The eggs are fertilized outside of both of their bodies (external fertilization) and hatch about 10 days later.

In the amplexus position, the male grasps on to the female from behind.
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Frogs

Frogs reproduce very similar to toads. Males and females use the amplexus position when they are ready to fertilize the eggs, and fertilization takes place externally. However, they have more variation in what they do with the eggs after. Frogs may leave fertilized eggs at the fertilization site like toads, but they may also bury them, or one of the adults will carry them on their body until they hatch. This is different from toads, which leave their eggs to incubate at the fertilization site.

Frog eggs are laid in water in high numbers.
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