por The life cycle of frogs consists of all the phases or stages that these animals pass through from the moment of their birth until their death. In most frogs, this process has the peculiarity that it takes place between two different environments: water and dry land.
When the frogs are born they live in the water during their entire juvenile stage. At this stage, frogs are very similar to fish, and are known as tadpoles. As the tadpoles grow in size and develop, they begin to develop legs for walking.
These legs are used to walk and move when they finish their development. When their legs are fully developed, the «tadpoles» leave the aquatic environment and start living on land.
Although adult frogs live mainly on dry land, they always depend on nearby bodies of water (such as lakes, ponds, rivers, or ponds) so that they can stay hydrated, find food, and also reproduce.
Frog life cycle stages
The life cycle of frogs can be defined in 4 different stages, during which these animals undergo an incredible metamorphosis, almost comparable to that of butterflies, for example. These stages are:
– the egg
– the tadpole
– the young frog
– the adult frog
Metamorphosis is the process of change by which frogs considerably change their physical appearances and physiological characteristics. Such changes are necessary to colonize land after having led a life in the water.
Some textbooks may omit or add more life stages to this short list, however, they always refer to the same ones that we will explain below.
1- Eggs
Frog eggs typically appear gelatinous and translucent, sort of like a «ball» of jelly. However, the appearance of the eggs can vary greatly depending on the species of frog.
Female frogs produce eggs inside their bodies, but only if the eggs come into contact with a male frog’s sperm (fertilization) can they give rise to viable eggs and form new frogs.
In frogs fertilization is external. This means that the females release the eggs through a hole in the back of their bodies, at which point the male mounts on top of the female and releases the sperm at the same time.
As soon as the female’s eggs come into contact with the male’s sperm, the eggs are fertilized by the male’s sex cells and the embryos that will become new frogs begin to develop inside.
Frog eggs are very permeable to environmental contaminants, which is why they are highly sensitive to environmental contaminants.
2- Tadpole
When the embryos have developed properly, the newly hatched «frogs» emerge from the interior of the egg as tiny larvae known as «tadpoles.»
Physically and physiologically, at that time, tadpoles are very similar to fish, even sometimes difficult to tell apart.
Tadpoles have a front part that is made up of a large head. The head is followed by a slender body, with small fins on each side, and a long rear tail that helps them swim.
Like fish, tadpoles have gills to breathe underwater, since they live in the water of lakes, ponds, puddles, rivers, etc.
Tadpoles are usually voracious predators of algae, since their growth and development is directly dependent on the amount of food they consume. It is estimated that, on average, a tadpole can feed on the same weight of algae per day, and that is a lot.
Over time, the tadpoles increase in size and begin to absorb the gills into their bodies, as these will become the lungs of adult frogs. In addition, they begin to develop legs on the sides of the tail and then in the middle of the body.
The tadpole’s circulatory system also undergoes major changes, which are necessary to be able to oxygenate the blood in the lungs (in the terrestrial environment) instead of oxygenating the blood through the gills (in the aquatic environment).
3- Young frog
Young frogs possess almost all the physical characteristics of fully grown (adult) frogs. However, sometimes young frogs still have a tail, are smaller than adult frogs, and their skin is very thin and sensitive.
In the short time that they remain as young frogs, the tail disappears, progressively decreasing in size, until it disappears completely.
At this stage, frogs have already developed a large mouth, lungs, and legs (front and rear), but they have not developed the ability to permanently breathe oxygen from the air, nor do they have much ability with their legs to move across the earth’s surface.
During this stage the young frogs begin to hunt small insects for food and become less and less dependent on the consumption of algae.
Although this stage of growth is usually very short, many researchers consider this stage to be different from that of an adult frog, since they do not exhibit the typical behavior seen in adults.
4- Adult frog
Adult frogs have well-developed, thick skin, often with warts and bumps. They have well-developed four legs, which they use to move with large jumps on the ground.
In addition, the legs are used to swim very efficiently, since they have webbed feet (they have membranes between the fingers), specially designed for swimming.
In adult frogs, the vocal cords, lungs and special cartilages in the mouth are highly developed to make sounds. Using these structures, frogs can communicate over great distances with each other.
These sounds are also used to warn other frogs about the presence of predators, to attract mates or simply to communicate with other frogs in the same environment.
The vast majority of frog species take 10-12 weeks to reach maturity from hatching. However, this time depends on the species of frog, the environmental conditions and the food available in it.
On average, frogs can live for 5-10 years, but some species can live for more than a decade. During this stage they constantly feed on insects and small vertebrates.
Themes of interest
Hummingbird life cycle.
Butterfly life cycle.
Turtle life cycle.
References
Hickman Jr, CP, Roberts, LS, & Larson, A. (1993). Integrated Principles of Zoology. 9th ed. Mosby-Year Book. Inc., St.Louis.
Hickman, CP, Hickman, FM, & Kats, LB (2000). Laboratory Studies in Zoology. McGraw-Hill Science/Engineering/Math.
Mayer, M., & Mayer, M. (1977). One frog too many. Puffins Books.
Royston, A. (2009). Frog (Vol. 16). Capstone Classroom.
Suzuki, D., & Tovell, V. (1987). Metamorphosis: Stages in a life. Stoddart.