WPC works to prevent the Oregon spotted frog from disappearing by building the wild populations in British Columbia, and studying the species to learn more about what is impacting these frogs. After a decline in breeding individuals of the Oregon spotted frog, Wildlife Preservation Canada began coordinating efforts in 2010 with the Greater Vancouver Zoo to build a recovery plan, and began breeding the frogs and releasing them to restored habitat.  Our team spends a great deal of time with the frogs, and monitor them as they transform from egg, to tadpole, to adult – and hopefully continue the process in the wild! 

How much do you know about frogs and tadpoles? Frogs and tadpoles are both the same creature, yet look vastly different and play different roles in their ecosystem.

Why do frogs go through this profound transformation, called metamorphis? 

The mystery of the tail

A question I get asked as a conservationist working with frogs is, what happens to their tail? Tadpoles sport an impressive tail that they use for movement in the water. Fogs and froglets do not have that same tail, so where does it go?

Many people’s initial thought is that the tail falls off. This is an understandable assumption, especially when many similar looking animals like lizards drop their tails for self-defence. However, this is not the case with frogs. As a tadpole goes through certain stages of metamorphosis it can’t eat anything at all and it absorbs its tail for nutrition. Let’s explore this further!

Munch, crunch, and lunch – The tadpole’s culinary journey

The diet and even feeding methods of tadpoles and frogs are very different.

Tadpoles are herbaceous filter feeders, they scrape algae off of surfaces and use specialised mouthparts called “oral discs”.

Frogs, on the other hand, are carnivores. Their diet consists of insects, spiders, small fish, worms, and some even eat other frogs! The digestive system for tadpoles is suited for plant matter but it needs to change in order to digest animal proteins when it becomes a frog. As you can imagine this major change takes some time. They can’t eat anything during that crucial stage.

From Gill to Gasp and Other Internal Changes

Tadpoles are true aquanauts! They rely on gills for breathing underwater, but their future froggy selves have other plans. As the tadpole matures, it starts developing lungs to breathe fresh air.

A tadpoles musculoskeletal system must also change. Tadpoles have a simple body structure suited for swimming, but as they become frogs, they develop a more complex musculoskeletal system to support jumping and other terrestrial activities.

Tadpoles excrete ammonia as waste, which is suitable for an aquatic environment, because it easily dissolves in water. As frogs become terrestrial, they develop a more complex urinary system, including functional kidneys, to excrete waste as urea, which conserves water more effectively.

Why go through metamorphosis?

Why go through all the effort, trouble and risk to metamorphosize and  be a frog?

Metamorphosis allows organisms to fill different roles or niches. Participating in metamorphosis allows organisms of the same species to avoid competition for resources between different life stages and serves various ecological functions in the ecosystem. Metamorphosis allows frogs to thrive in different habitats during different life stages. They start their life cycle in the water as tadpoles, where they can take advantage of aquatic resources, and then transition to a terrestrial lifestyle as adults, enabling them to explore a wider range of ecological niches.

Can you think of another organism that undergoes metamorphosis ?

Hint: It’s another one of our animals in a recovery program at the Greater Vancouver Zoo.

Rajdeep Singh

Conservation Technican, BC Conservation

Raj has been part of the WPC team for two seasons, contributing to the captive breeding program at the Greater Vancouver Zoo. He enjoys being directly involved with animals and educating the public. Currently, Raj is in his third year at the University of British Columbia, working towards a degree in Natural Resource Conservation.

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