The anurans, commonly called frogs and toads, are a group of amphibians and their name derives from the prefix an=without (or negation) and uro=tail, so they are amphibians thatthey do not have a tail in the adult state They are ectothermic organisms and, due to this, they reproduce and grow during the most favorable and warm season of the year. Like other amphibians, frogs start reproducing in the water, and during the spring, males start croaking to attract females. They are common in almost the entire planet, with the exception of polar areas, deserts, Madagascar and part of Australia.
In this Article on our site, we will tell you all about the frog life cycle, the changes that occur during this process and the characteristics of its reproduction.
Reproduction in frogs
Anurans or frogs are dioecious amphibians, that is, they have the sexes separated, and they have differences between males and females (dimorphism sexual). When the favorable season for frogs begins, that is, spring, it is when the females have their eggs already matured, at which time they enter the water to meet with the male for copulation.
This occurs through a "hug" by the male to the female (the amplexus) and can be inguinal or axillary, that is, embraced from the groin or armpits. The fertilization is external and, as the females lay their eggs, the male releases the sperm-laden seminal fluid onto them, thus fertilizing them. The eggs are then covered by gelatinous layers that absorb water and swell. Many times they are placed attached to aquatic vegetation, or inside plants in the form of a rosette, this varies according to the types of frogs. As the eggs do not have a cover to protect them from desiccation, they are placed in large masses of eggs that are joined by a gelatinous substance. This protects them against shock, pathogenic organisms, and against predators.
How are frogs born?
From the eggs emerge the young in the larval stage, called tadpoles. They live in water, while adults can lead a semi-terrestrial life (hence the name amphibian) although they always need wet places or close to water sources. In frogs there are parental care, which, although they may be scarce, are present in various species of frogs:
- R-Strategy: Most are “R-Strategists”, meaning they have many offspring that they take little care of once that are born In this way, if they have many offspring, even if some die, enough will survive to perpetuate the species.
- K-Strategy: However, some species are “K-strategists”, such as the Surinam toad (Pipa pipa), Darwin's frog (Rhinoderma darwinii) and frogs of the Oophaga genus, such as the poison dart frog (Oophaga pumilio). As for the latter, it lays its eggs on the forest floor and then the male protects them from possible predators. Also, to keep them moist, the father carries water in his sewer to wet them. Once the young hatch, the female carries the tadpoles on her back until she places them inside cups that form rosette-shaped plants, such as bromeliads. In these cases, the female feeds the tadpoles with unfertilized eggs until the young are strong and large enough for metamorphosis to occur.
Metamorphosis of the frog
After the tadpoles hatch from their respective eggs, the hatchlings go through a transformation process, called metamorphosis, until they reach its adult phase. Next, we will stop at each of the frogs' phases.
Life Cycle of Frogs
In short, we could say that the life cycle of frogs corresponds in this way:
- Egg laying.
- Birth of the tadpoles.
- Transformation from tadpoles to adult frogs.
- Reproduction of adult frogs.
This cycle can also be divided into three phases or stages:
- Embryonic stage of frogs.
- Metamorphosis phase in frogs.
- Adult phase in frogs.
Next, you can see the image that we attach below with the cycle of the frog.
For more information on how frogs reproduce, you can consult this other article on our site about Frog reproduction.
Embryonic stage of frogs
Egg development begins almost immediately and undergoes some transformations. Some of them are:
- Blastula formation: by a series of repeated divisions, that is, by cleavage, the egg becomes a hollow mass of cells (the blastula).
- Gastrulation: once the blastula is formed, it undergoes gastrulation, that is, cell differentiation continues, a process that will form the system digestive. At this time, the cells are loaded with yolk (through which the embryo feeds). Once gastrulation is complete, cell differentiation occurs, where each cell is differentiated, specialized and performs specific functions. At this point, an inner layer called the endoderm has differentiated, which will give rise to the internal organs, and an outer layer, the ectoderm, which will differentiate into external organs such as the skin.
- Neurulation: neurulation occurs later, beginning with a thickening of the neural plate, which will later differentiate into the notochord of the embryo and later it will give to the nervous system of the tadpole and adult.
After about 6 or 9 days, depending on the species, is when the tadpoles hatch. The embryo emerges from the egg and its gelatinous layer that protected it.
Embryonic stage of frogs: exceptions
As we mentioned, the larvae are entirely aquatic, but there are species, such as the Sri Lankan rock frog Nannophrys ceylonensis, which have tadpoles that are semi-terrestrial and live among wet rocks.
Frog metamorphosis phase
We could divide the frogs' metamorphosis phase into two, since different transformations occur in each of them.
Frog larval stage
Once the larva or tadpole hatches, it has the following characteristics:
- Differentiated head and body.
- He has no limbs.
- Compressed queue.
- Mouth in ventral position.
- Horny jaw (keratinized)
- Ventral adhesive disk behind the mouth to attach to objects.
- Gill respiration.
The feeding of baby frogs is based on vegetables during the larval stage, for which they have rows of little teeth around the mouth (called labial teeth). They can be omnivorous, since depending on the environmental conditions, they can adapt and even become carnivorous, some species becoming cannibalistic.
In this other article we explain in more detail the feeding of frog tadpoles.
Tadpole to adult frog phase
Once the tadpole reaches the necessary maturity, it begins a transformation process called metamorphosis, in which the following gradually occurs:
- The legs are differentiated, first the 2 rear ones and then the 2 front ones.
- Skin pigmentation (slightly).
- The glue is reabsorbed by apoptosis (controlled cell death).
- Development of the lungs.
- Gills are also reabsorbed
- Pulmonary and skin respiration.
- Development of the circulatory and nervous system.
- Differentiation of the eyes and eyelids.
- Development of muscular tongue.
- Development of the auditory system.
Frog metamorphosis stage: exceptions
Depending on the species, these changes can take from a few months to two or three years. There are species that can undergo metamorphosis even inside the egg and emerge as miniature adults.
Adult phase of frogs
Once the metamorphosis has occurred, the young adults disperse in terrestrial environments or can continue living in the water, this will depend on each species. Almost all species as adults have carnivorous feeding habits and, depending on the species, feed on:
- Arthropods.
- Worms.
- Snails.
- Other invertebrates.
- Other frogs.
- Little fishes.
- Mammals.
Others hunt by stalking and use their sticky tongues to catch prey, while others carry food to the surface using their hands. On the other hand, Xenohyla truncata is an exception, since being herbivorous, its diet includes a large proportion of fruits To learn more about it, you can consult this article on What do frogs eat? - Feeding of the frogs.
Later, the frogs will reach sexual maturity (the time varies in each species and is highly dependent on the environmental context) for which which will be ready to mate and reproduce.
Now that you know what the life cycle of frogs is, if you want to know the characteristics of frogs, we encourage you to read this other article on our site about Characteristics of amphibians.
