Development of Plains Leopard Frog Embryos

By Greg and Lynnette Sievert

Plains Leopard Frog - (Rana) Lithobates blairi

Plains Leopard Frog egg mass

Plains Leopard Frog egg mass. Each embryo has a light region and a dark region. The light cells are the cells that contain yolk. The smaller, dark cells are the cells that will become the embryo's body.

Dorsal Lip. The dorsal lip of the blastopore on the upper embryo is the place where cell differentiation begins. The dorsal lip is the thin, U-shaped, dark line. The lower embryo, which is slightly out of focus, has formed a yolk plug.

Plains Leopard Frog egg with blastopore. The entire blastopore has formed and looks like a dark circle (embryo on left). This is where the dark embryo cells that started on the surface dive into the inside of the embryo. The cells that stay on the surface will become skin and nervous system. Those that go inside of the embryo will become all of the other body parts. The lighter cells are the yolk plug which are the only yolk-filled cells left on the surface.

Plains Leopard Frog Yolk Plug Stage. See the individual cells that make up the yolk plug.

Early embryo. Initially the number of cells increases but the size of the embryo does not. Each embryo is surrounded by a jelly-like clear substance.

Look at the embryo just to the left of center. Although this embryo is still the same size as the last ones, it has started neurulation - the development of the nervous system. The groove going down the back of the embryo is the neural groove, the raised areas on either sides are the neural folds.

Here you can see that the front end of the embryo has larger neural folds than the posterior part. The larger neural folds will become the brain and the narrower folds will become the spinal cord.

The neural folds have joined together now forming a tube - the neural tube. Notice the large "belly" of the embryo. It contains cells filled with yolk. This is where all of the calories and nutrients that allow growth and development are stored.

These embryos do not have mouths yet. The projection on the head is the beginning of the adhesive glands. These will be important in allowing the embryo to stick to vegetation once it hatches but has not started feeding yet.

Notice how large the head is relative to the rest of the body. Development of the head proceeds at a very rapid rate.

These embryos have just hatched. The embryo that is center left and the embryo that is center bottom have the adhesive glands showing. They almost look like stumpy little legs.

These embryos have started growing their tails. At this point they are very poor swimmers and spend their time attached to vegetation digesting their yolk and developing.

These tadpoles are continuing to use their yolk for energy and nutrients. Their bodies are growing longer and so are their tails.

This shows several different developmental stages.

See how one of the embryos is moving. Even though their eyes and brains have a long way to go in development they can detect differences in light levels and respond to them. While photographing them they would move their heads away from the light - even before they had hatched.

At this point in development the eyes and external gills are visible.

The shape of the body is now becoming much more tadpole-like. These embryos still have the adhesive glands, are living off their yolk, and have external gills.

See how the yolk is smaller? At this stage you can see the eyes developing and see the digestive tract. These embryos still have their adhesive glands.

Now the eyes are very obvious, the body looks like that of a tadpole's and these animals are able to swim and feed for themselves.

This is a mature tadpole. The back legs are obvious and the front leg is about to emerge. This tadpole will be metamorphosing in a short time.

Graduate study in Herpetology at Emporia State University

Last updated on 22 January 2014

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