More frog breeding

We first observed breeding by our resident frog species in Spring/early Summer 2016. At the end of Autumn 2017, following a couple of rainy days, we were excited to discover fresh egg masses in our pond. A quick check under the microscope showed that these were at an early stage of embryonic development - the early tailbud stage. So we now had the opportunity to follow their development through to the tadpole and ultimately adult stage. To this end, we set up an aquarium, housing over 150 embryos. We imaged embryos at regular time intervals to chronicle the developmental changes.

This is a tailbud stage embryo. The bulge on the left is the developing tail. While the embryo looks quite formless, it already possesses early versions of most of the internal organs. 

The same embryo viewed from above. The ridge along the back marks the developing spinal cord, while the bulges on each side at the right end show where the brain is developing.

This is the exact same embryo just 20 hours later. The tail has lengthened. The dark spot in  front of the brain bulge is the developing eye. The dark spot on the bottom side of the head is an adhesive organ, used to hold onto a surface after hatching.

This shows a jelly mass attached to a plant stem. It contains a cluster of embryos about 4 hours older than the one in the previous image. Each embryo is encased in its own egg membrane.

This embryo is 24 hours older than the previous one. Clear fins are now evident on the lengthening tail. The darker central area of the tail contains the spinal cord, surrounded by V-shaped muscle blocks. External gills have now developed.

This movie shows a close up of the external gills in an embryo at the same stage as that in the previous still image. Blood cells can be seen coursing through the gills, picking up oxygen from the surrounding water.

blood flow in frog embryo gills from Paul Whitington on Vimeo.

Just two days after the tailbud stage, we noticed that some of the embryos were activelytwitching in their egg membranes. 

frog embryos twitching in egg membranes from Paul Whitington on Vimeo.

Two days later, the first tadpoles burst out of the jelly mass. For a while, they lay quite still, attached to a surface by their adhesive organs. At this time, the tadpole is feeding off yolk carried over from the egg, which becomes incorporated into the gut in the course of embryonic development. So it doesn't need to seek food externally.

This is a freshly hatched tadpole. The eye is well developed and the gut now opens to the surface.

However, within a day or so, the tadpoles began actively swimming around in search of food. They love boiled spinach! 

These guys have done a good job on this spinach leaf!

The golden flecks over the body identify this tadpole as Litoria ewingii.

This close-up shows the dark "teeth", just inside a whitish fringe which surrounds the mouth. The external gills have been replaced by internal gills, which lie beneath a transparent cover.

Our babies are growing apace! We'll keep you in touch with their progress in future posts. 

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