Our Little Frogy is Hiding and Yes It is!

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Have you ever wondered why frogs are green in colour or brown or even a mix of these colours, and why does their skin always have to be slimy?

Well the answer is quite straight forward. These colours are used as a protective characteristic in camouflaging the animal in its natural surroundings. Though our little pet does not have to worry about predators, this camouflaging behavior is a defensive attribute that has been adopted by all, if not most frogs. To some extent they do have the capability to change their skin colour. This is done by expanding or contracting the pigment cells in the skin, thus making the frog look darker or lighter.

On the second part regarding its skin, why does it have to be slimy? Well frogs don’t drink water. They absorb water through their skin. Frogs are slimy because their skin is covered in a layer of mucus. This mucus helps the skin retain moisture thus hydrating our little buddy at all times. Frogs also use their skin to breathe as its skin is permeable to water and air. Also, their slimy skin functions as another defensive attribute, where it makes the frog slippery thus easily able to escape from predators.

Application in Biomimicry 

Although camouflaging is not a specific characteristic that is observed only from frogs, but this observation has triggered me on this idea. Armed forces around the globe have used this idea as a war tactic in battlefields. The uniform, military equipment as well as their heavy vehicles are as the same colour of the environment. this makes it difficult for them to be spotted by their enemies. 

The slimy skin of frogs would not make an attractive feature in engineering design, however its behavior as a membrane that allows water and air to diffuse makes it very much interesting to apply. Semi-permeable membranes such as the reverse osmosis membrane as seen in the figure below are widely used in water purification which functions with the same concept of a frog skin. 

  

Inspiration of Toe Pads of Frogs

Dear readers, welcome to another update on our pet tadpole which metamorphosed into a frog! 

(Unfortunately, only one tadpole managed to morph and the others did not survive due to aggression between tadpoles during the stage of metamorphosis) 

Our pet tadpole (now turned frog) is alive and healthy!

A new environment has been set up as the froglet no longer lives in water but now primarily lives on land.
The drastic change in behavior and characteristics of tadpoles to frogs often amazes us as they turn from living in water to land, breathing from with gills to lungs and skin and from a herbivorous diet to insect-eating carnivores.

An artificial habitat was created using soil, rocks, pebbles, plants and water in a fish tank and is designed to mimic the natural habitat of the frog in order to ensure that the frog lives in a healthy and natural environment.
Bread was placed in the artificial habitat to attract small insects which made up the diet of the froglet.

Through our observation of the froglet, it has a strong grip on its limbs and it has an amazing ability to attach and move around walls, leaves and pebbles without slipping or falling off. 

We were very interested in learning about how the froglet manages to do that and maybe we could obtain some inspiration from the limbs or toes of the frog.

Therefore, some reading has been done and it was discovered that frogs actually have attachment pads consist of hexagonal arrays of approximately 10μm in size and is separated by a gap of approximately 1μm wide on their toe pads which can be seen in part c of the figure below.

(Source: Federie et al., 2006)

These hexagonally-shaped epidermal cells allows them to attach on slippery surfaces by means of wet adhesion. When the frog is climbing through wet surfaces, it squeezes out water from the contact surface through the 1μm gap between its hexagonal epidermal cells and this creates a tight grip that secures the position of the frog, enabling it to firmly and steadily hang on steep, wet and slippery surfaces.

(Source: Ambiguous @ Flickr, 2006)

Astonishingly, patterns and treads on tires were actually created by mimicking the toe-pads of frogs! 

Treads on tires we designed as such that when a car is being driven on a wet road, water flows out through the channels between the treads, thus increasing the friction between tires and road surfaces and ultimately provides a firm grip which significantly lowers the exposure of risks of accident when driving under wet conditions.

Other possible applications of this mechanism can also be applied to the shoes of mountain climbers or trackers to improve the grip of climbers on slippery or wet surfaces to prevent accidents which may be life-threatening when climbing at steep or high altitudes. 

Thank you! :)

Further reading:
Biomimetics: Lessons from Nature – An Overview

Tadpoles to Frog!

In the figure below, the life cycle and completion of a tadpole to a frog is indicated.
Generally, tadpoles undergo 10 stages in order to completely grow and develop into frogs.

Figure 1: Metamorphosis Process (source: www.toadrescue.co.uk)

1: Toad Spawn

2-3: Developing ova

4-5: Tadpoles with external gills

6-7: Development of rear limbs

8-9: Development of front limbs

10: Metamorphosis to a toad

Step 1 to 6 are demonstrating first four weeks of a tadpole. Starting from Week 6, it was observed that they started developing body parts first front and eventually in Week 7 back legs. 

However, it was observed that some tadpoles are still younger than others and have not developed to that level yet.

 Figure 2: Tadpoles

As it can be seen in Figure 1, some of the tadpoles are developing back legs in 6th week.

 Figure 3: A tadpole with its hind leg developed

Figure 3 is an indication of the development process of tadpoles in Week 7, some of them have been developing both front and back legs.

Figures 4 & 5: Tadpole with front and back legs and already shaping to a frog.

Figures 4 and 5 are demonstrations of a tadpole to frog and the 9th step of development which is developing front limps and entering to 10th step which is becoming a complete frog.

The noticeable development and inspiration form them was the respiration system the have developed. It was observed that at this stage they prefer not to be in water all the time but rather to breath and getting on top of the water with occasional swimming.

Tadpoles absorbs oxygen through the water passing their mouth and pass the carbon dioxide through their gills. However frogs are exchanging these gases through their skin.