Development of Boreal Chorus Frog Embryos

By Greg and Lynnette Sievert

Chorus Frog - Pseudacris maculata

Chorus Frog egg mass on a blade of dried grass

Chorus Frog egg masses. The mother placed her eggs around a dried blade of grass in the water.

Not all eggs survive. These eggs are being eaten by a fungus.

Chorus Frog egg. This very early embryo consists of a number of identical cells. If you look you can see the individual cells on the surface of the embryo.

Chorus Frog dorsal lip. The U-shaped structure is the dorsal lip of the blastopore. As cells move from the outside of the embryo through the dorsal lip they start to develop into specific structures. This is called differentiation.

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. The dried blade of grass in this picture is the same blade of grass that is in the first two pictures. Notice how magnified the grass blade and individual eggs are. These embryos are at the yolk plug stage of development. The dark colored cells that will become the body of the frog surround the light, yolk-filled cells, except at the yolk plug.

This is a closer look at the embryos during the yolk plug stage. See how magnified the grass blade and individual embryos are? Notice the darker streaks on some of the embryos. These cells are rapidly moving and because of the movements there are what look like streaks on the embryo.

The brain and spinal cord are begining to develop. The nervous system at this point consists of two ridges with a groove in between.

The front end of the neural groove where the brain will form is wider than the posterior end where the spinal cord will form. The two neural ridges will come together and form a neural tube.

These embryos still have not hatched and you can see they are still contained within a membrane. These embryos are sitting in a U position (bent backwards). The yolk-filled cells are in the belly region (at the bottom of the U) and provide nutrients and energy for continued growth.

Notice how large the head is relative to the rest of the body. Development of the head proceeds at a very rapid rate. In these embryos you can see the head, belly and developing tail.

These embryos continue to grow longer and the tail is becoming longer.

The head of this embryo is facing you. At the left end of the head you can see the adhesive glands. These will allow the embryo to stick to plant material once it hatches.

These tadpoles are continuing to use their yolk for energy and nutrients. Their bodies are growing longer and so are their tails. These embryos will be hatching very soon.

This shows a closer view of tadpoles nearing hatching. At this point they are still developing their sensory organs, but you can see an indentation that will be the nose and bulges that will become the eyes. The external gills are starting to form.

This shows a newly hatched tadpole. At this point it is still reabsorbing yolk and is a very weak swimmer.

This shows a young tadpole.

The mouthparts of a tadpole are used for rasping algae and other tiny bits of food. The dark tooth rows are made of keratin (like your fingernails) and are distinctive for each species. Identification of tadpoles sometimes relies on looking at the tooth rows. On the right side you can see the spiracle sticking out from the tadpole. This is used for exhaling water. This animal spends most of its time eating.

This tadpole has developed its hind legs.

Graduate study in Herpetology at Emporia State University

Last updated on 23 January 2014

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