Frog breeding and care. The birth of a frog. How does this happen? Very difficult program

What a frog looks like - everyone knows in the world. How is a frog born? Is it true that different types of frogs reproduce and care for their offspring in different ways?

In this article we will talk about how nature arranged the process of the birth of the most. As a rule, these amphibians are born in a pond or lake. The female frog leaves eggs only in stagnant water. After a certain period of time, tadpoles appear from the laid eggs, then they turn into small frogs ... so we used to think, looking at the frogs that live in our country, but in fact ...

In fact, not all frog species reproduce in the same way. The main "innovators" in the reproductive field are those frogs that live in the tropics. Firstly, the number of species of tailless amphibians that we are talking about in tropical zones exceeds all conceivable ideas. A large number of predators, who now and then want to eat frog eggs, makes these amphibians invent a variety of ways to save future offspring.

Birth of glass frogs

Females produce caviar, which looks like a gelatinous mass. This "mass" is attached to the back of the sheet (it is important that the sheet is located directly above the water). The father of the family becomes a guard for future offspring. When the tadpoles emerge from the eggs, they slide off the leaf directly into the pond and there is already a further transformation into an adult.

Birth of the South African frog

Have you heard of "foam houses"? This is not just an unusual substance, but a real hiding place in which South African frogs hide their eggs. How is foam formed? In order to create such a “house”, the female frog secretes a special substance, and the industrious male beats it into foam. The top layer of the foam house hardens and the eggs can comfortably continue to develop inside without fear of being eaten.

Birth of poison dart frogs

Poisonous South American frogs also give life to their offspring in an unusual way. They, like their other relatives, lay eggs (by placing them on moist soil). Then they carefully and very jealously guard the eggs. Well, when the tadpoles emerge from the eggs, they immediately climb onto their back to their parent. For what? To move from the ground to the tree. Having found the leaves of the bromeliad plant (which winds around the trees), the mother frog places the tadpoles in a funnel at the base of the bromeliad leaf (where water always accumulates after rains). Here the tadpoles find a temporary shelter until their parent finds a nearby body of water and transfers them to it for later maturation.

Birth of the pygmy marsupial tree frog

Yes, yes, you heard right “marsupial”. By the way, the birth of cubs in this frog is similar to the way of reproduction in kangaroos. The frog has a special pocket made of leather, where the laid eggs are placed. Unlike the kangaroo, the tree frog has a pocket on its back. So a caring mother carries her future babies until the time comes for them to become tadpoles. Then the tree frog carries the future frogs to the reservoir and releases them.

The birth of the rain frog

The unusual structure of the eggs of these frogs makes it possible to be born not as a tadpole, but immediately as a small adult. The fact is that the internal composition of the egg is such that it has a sufficient supply of nutrients for the tadpole to feed and live to become a frog without leaving the egg shell.

Frogs, gametogenesis, fertilization and other seasonal activities depend on numerous external factors. The life of almost all amphibians depends on the number of plants and insects in the pond, as well as the air and water temperature. Different stages of development of frogs are distinguished, including the larval stage (egg - embryo - tadpole - frog). The metamorphosis of a tadpole into an adult is one of the most striking transformations in biology, as these changes prepare an aquatic organism for terrestrial existence.

Development of frogs: photo

In tailless amphibians, such as frogs and toads, metamorphic changes are most pronounced, almost every organ undergoes modification. The shape of the body changes beyond recognition. After the appearance of the hind and forelimbs, the tail gradually disappears. The cartilaginous skull of the tadpole is replaced by the facial skull of the young frog. The horny teeth that the tadpole used to eat pond plants disappear, the mouth and jaws take on a new shape, the muscles of the tongue develop more strongly to make it easier to catch flies and other insects. The elongated large intestine characteristic of herbivores shortens to accommodate the adult's carnivorous diet. At a certain stage in the development of frogs, the gills disappear, and the lungs increase.

What happens immediately after fertilization?

Soon after, it begins to move from one cell stage to another in the process of division. The first cleavage starts at the animal pole and runs vertically down to the vegetative pole, dividing the egg into two blastomeres. The second cleavage occurs at right angles to the first, dividing the egg into 4 blastomeres. The third furrow is at right angles to the first two, being closer to the animal than to the vegetative pole. It separates the top four small pigmented areas from the bottom four. At this stage, the embryo already has 8 blastomeres.

Further splits become less regular. As a result, a unicellular egg gradually turns into a unicellular embryo, which at this stage is called a blastula, which, at the stage of 8-16 cells, begins to acquire spatial cavities filled with liquid. After a series of changes, a single-layer blastula turns into a two-layer embryo (gastrula). This complex process is called gastrulation. The intermediate stages of frog development at this stage involve the formation of three protective layers: ectoderm, mesoderm and endoderm, which are also known as primary. Later, larvae hatch from these three layers.

Tadpoles (larval stage)

The next after the embryo is the larva, which leaves the protective shell already 2 weeks after fertilization. After the so-called release, the frog larvae are called tadpoles, which are more like small fish about 5-7 mm long. The body of the larva includes a distinct head, trunk and tail. The role of the respiratory organs is played by two pairs of small external gills. A fully formed tadpole has organs adapted for swimming and breathing; the lungs of the future frog develop from the pharynx.

Unique Metamorphoses

The aquatic tadpole undergoes a series of changes that eventually transform it into a frog. During metamorphosis, some larval structures are reduced and some are changed. Metamorphoses initiated by thyroid function can be divided into three categories.

1. Changes in appearance. Rear limbs grow, joints develop, fingers appear. The forelimbs, still hidden by special protective folds, come out. The tail shrinks, its structures break down and gradually nothing remains in its place. The eyes from the sides pass to the top of the head and become bulging, the lateral line organ system disappears, the old skin is shed, and a new one, with a large number of skin glands, develops. The horny jaws fall off along with the larval skin, they are replaced by true jaws, first cartilaginous and then bony. The gap in the mouth increases significantly, allowing the frog to feed on large insects.

2. Changes in internal anatomy. The gills begin to lose their importance and disappear, the lungs become more and more functional. Corresponding changes occur in the vascular system. Now the gills gradually cease to play a role in blood circulation, more blood begins to flow into the lungs. The heart becomes three-chambered. The transition from a predominantly plant-based diet to a purely carnivorous diet affects the length of the alimentary canal. It shrinks and twists. The mouth becomes wider, the jaws develop, the tongue enlarges, the stomach and liver also become larger. The pronephros is replaced by mesospheric buds.

3. Lifestyle changes. During the transition from larva to adult stage of development of frogs, with the onset of metamorphosis, the lifestyle of an amphibian changes. It often rises to the surface to gulp air and inflate the lungs.

Frog - a miniature version of an adult frog

From the age of 12 weeks, the tadpole has only a small remnant of the tail and looks like a smaller version of the adult, which, as a rule, completes a full growth cycle by 16 weeks. The development and species of frogs are interrelated, some frogs that live at high altitudes or in cold places can live in the tadpole stage all winter. Certain species may have their own unique developmental stages that differ from the traditional ones.

Frog life cycle

Most frogs breed during the rainy season, when ponds are flooded with water. Tadpoles, whose diet differs from that of adults, can take advantage of the abundance of algae and vegetation in the water. The female lays eggs in a special protective jelly under water or on plants located nearby, and sometimes does not even care about the offspring. Initially, the embryos absorb their yolk reserves. Once the embryo has turned into a tadpole, the jelly dissolves and the tadpole emerges from its protective shell. The development of frogs from eggs to adults is accompanied by a number of complex changes (appearance of limbs, reduction of the tail, internal restructuring of organs, and so on). As a result, the adult individual of the animal in its structure, lifestyle and habitat differs significantly from the previous stages of development.

In this article, we will consider the stages of frog development. But first, let's talk a little about what these creatures are. The frog belongs to the class of amphibians, the order of anurans.

Many noticed that her neck was not expressed - it seemed to have grown together with the body. Most amphibians have a tail, which the frog does not have, which, by the way, is reflected in the name of the detachment.

The development of a frog takes place in several stages, we will return to them immediately after we analyze some of the features of these creatures.

What does a frog look like

For starters, the head. Everyone knows that the frog has rather large and expressive eyes located on both sides of its flat skull. Frogs also have eyelids; this feature is inherent in all terrestrial vertebrates. The mouth of this creature has small teeth, and a little above it are two nostrils with small valves.

The forelimbs of frogs are less developed than the hind limbs. The first have four fingers, the second - five. The space between the fingers is connected by a membrane, there are no claws.

The development of a frog takes place in several stages:

1. Caviar throwing.
2. Early stage tadpoles.
3. Late stage tadpoles.
4. Adult individuals.

Their fertilization is external - the males fertilize the eggs already laid by the female. By the way, there are species that lay more than 20 thousand eggs in one throw. If everything goes well, then ten days later tadpoles are born. And after another 4 months, full-fledged frogs are obtained from them. Three years later, a mature individual grows up, which is completely ready for reproduction.

Now a little more about each stage.

Caviar

Now we will analyze all the stages of frog development separately. Let's start with the very first - eggs. Although these creatures live on land, during spawning, they go into the water. This usually happens in the spring. Masonry takes place in quiet places, at a shallow depth, so that the sun can warm it up. All eggs are interconnected, and this mass resembles jelly. One teaspoon is barely enough from one individual. All this jelly mass is necessarily attached to the algae in the pond. Small species lay about 2-3 thousand eggs, large individuals - 6-8 thousand.

The egg looks like a small ball, about 1.5 millimeters in diameter. It is very light, has a black shell and increases in size over time. Gradually, the eggs move on to the next stage of frog development - the appearance of tadpoles.

tadpoles

After birth, tadpoles begin to feed on the yolk, which still remains in small quantities in their intestines. This is a very fragile and helpless creature. This individual has:

• poorly developed gills;
• tail.

Tadpoles, in addition, are equipped with small Velcro, with which they are attached to various water objects. These Velcro are located between the mouth and abdomen. In the attached state, the babies are about 10 days old, after which they begin to swim and eat algae. Their gills gradually overgrow after 30 days of life and, as a result, are completely covered with skin and disappear.

It is also important to know that even tadpoles already have the small teeth necessary to eat algae, and their intestines, arranged in the form of a spiral, allow them to extract the maximum nutrients from what they eat. In addition, they have a chord, a two-chambered heart and blood circulation in the form of a single circle.

Even at this stage of frog development, tadpoles can be considered quite social creatures. Many of them interact with each other like fish.

The appearance of the legs

Since we are considering the development of a frog in stages, the next step is to single out tadpoles with legs. Their hind limbs appear much earlier than the front ones, after about 8 weeks of development - they are still very tiny. In the same period, you can notice that the head of the kids becomes more distinct. Now they can eat larger prey, such as dead insects.

The forelimbs are just beginning to form, and here one can single out such a feature - the elbow appears first. Only after 9-10 weeks will a full-fledged frog form, however, much smaller than its mature relatives, and even having a long tail. After 12 weeks, it completely disappears. Now the little frogs can go on land. And after 3 years, a mature individual will form and will be able to continue its genus. We'll talk about this in the next section.

adult

After three long years have passed, the frog can reproduce into the world. This cycle in nature is endless.

To consolidate, we once again list the stages of development of the frog, the scheme will be our assistant in this:

a fertilized ovum represented by an egg - a tadpole with external gills - a tadpole with internal gills and skin respiration - a formed tadpole with lungs, limbs and a gradually disappearing tail - a frog - an adult.

Frogs are the most famous tailless amphibians. Occupy an intermediate position between terrestrial and aquatic vertebrates.
The life of amphibians deserves attention, primarily because they occupy a special place in the history of the development of terrestrial vertebrates, being the first and most primitive inhabitants of the land. It is possible to assess the importance of amphibians in nature and human economic activity with further study of amphibians, whose biology has been developed only extremely superficially. The use of this animal for the study of biology gave recognition to the great merits of the frog in medicine.

Firstly, the lake frog is an exterminator of harmful animals. This representative of the amphibian order in its adult state feeds exclusively on animal food and, living in a wide variety of places, benefits by eating harmful insects. The importance of amphibians also increases because they eat insects with an unpleasant odor and taste, as well as insects with a protective color, in larger numbers than birds. Particularly noteworthy is the fact that land species of amphibians hunt at night, when the vast majority of insectivorous birds are sleeping.

Secondly, amphibian frogs are a food base for some fur-bearing animals. Frogs make up more than one third of all mink food - a valuable fur-bearing animal confined to water bodies. Willingly eats amphibians and otters. Relatively often amphibians are found in the stomachs of badgers and black polecats. Finally, many commercial fish in lakes and rivers in winter consume large quantities of frogs, which turn out to be quite affordable mass food.

Of course, there are also negative aspects when frogs exterminate juvenile fish in large quantities. Attracted by clusters of fry, numerous lake frogs turn out to be their main enemies here.

In some cases, frog tadpoles can compete with fish for food. Recently, there have been indications of the negative significance of amphibians in nature as guardians of dangerous infectious diseases, such as tularemia.

Thirdly, amphibians are evaluated as laboratory animals. The frog's ease of preparation, suitable size, and vitality have made it a favorite test subject for a long time. Most of the instruments of experimental medicine and biology are designed for this animal. The technique of physiological experiment is constantly developed on the frog. A huge number of experiments and observations have been and are being carried out on these “martyrs of science”. Laboratories of large educational and scientific institutions consume tens of thousands of frogs a year. This expense may be so great that it is necessary to take measures so as not to destroy all the animals. So, in England, frogs are now under the protection of the law, and catching them is prohibited.

Thus, the question arises about the relevance of growing frogs in an artificial environment.

All this made it possible to determine the topic of scientific work.

Purpose of the study: find out under what different, artificially created conditions, the frog larva will go through all the stages of metamorphosis faster.

Research objectives:
1. Study the scientific literature on biology;
2. Identify the causes of positive and negative environmental impacts on development;
3. Conduct research work.

Object of study: caviar of an ordinary frog.

Hypothesis: Various environmental conditions affect the development of a frog from spawn to individual in an unnatural habitat. If you create all the necessary conditions, then you can achieve the maximum percentage of survival of tadpoles.

Reliability of results provided by the personal participation of the author in the research process.

lake frog

Description

The lake frog is a species of tailless amphibians of the family of real frogs. The lake frog is the largest species of amphibian fauna of Russia: its body length can reach up to 150 mm.

Tailless - the largest order of amphibians, numbering about 6000 modern and 84 fossil species. Often, representatives of the order are called frogs, but the use of this term is complicated by the fact that only representatives of the family of real frogs are called frogs in the narrow sense. Tailless amphibian larvae are tadpoles.

Class - Amphibians, detachment - Tailless, family - Frogs, Genus - Frogs.

Size 6-10 cm. Average weight 22.7 gr. The muzzle is blunt, the body is squat. The eyes are brown with black horizontal pupils. The inner eyelid is transparent, protecting the eyes in water. A dark brown triangle is clearly visible near the tympanic membrane. The skin of the frog is slimy and smooth to the touch, its epidermis does not keratinize. There is a marble-like pattern on the dark belly. Calcaneal inner tubercle is low.

In males, external resonators of a dark gray color are located in the corners of the mouth. On the first (inner) finger of the forelimbs, males have a skin thickening - a callus, which grows during mating.

Amphibians require oxygen to live. The frog can get it on land and partially under water through the skin. The respiratory organs of amphibians, which include frogs, are lungs, skin and gills. Unlike tadpoles, which are aquatic, adult frogs do not have gills. Oxygen dissolved in water enters the blood of these creatures through the skin. This way of breathing can provide the body with the necessary gas only if the frog is in a state of hibernation.

A frog can be under water for a long time, because. she has very large lungs. Before diving, the animal gains full lungs of air. Under water, oxygen is absorbed very slowly through the blood arteries, and this helps the frog to stay under water for a long time. As soon as the air supply runs out, the animal quickly emerges and keeps its head above the surface of the water for some time in order to regain full lungs of air.

Frogs never drink. Fluid enters their body through the skin.

An adult breeds in water, but prefers to spend most of its life on land, choosing very damp and shaded places to live.

On land, frogs hunt by catching insects, which are the main diet. In gardens located in the lowlands near water bodies, fruit trees, shrubs and vegetable crops are almost never affected by pests, since frogs are cleaning animals. Only a few frogs are capable of destroying hordes of insect pests.

The breeding season is April - early May. Reproduction occurs in puddles, reservoirs, lakes, canals, in any shallow reservoir. Spawning begins 3-5 days after awakening. Males appear on the reservoirs earlier, they sing mating songs, inviting females. Having spawned, the common frog does not linger in the reservoir and disperses to summer habitats. The eggs are light yellow in color, surrounded by a thick layer of gelatinous substance. This shell is of great importance for the embryo, since in this way the egg is protected from drying out, from mechanical damage, and most importantly, it protects them from being eaten by other animals. They are connected in clusters of a rather significant size, and sometimes in cords; a lot of them are put off. One female lays 670-1400 small eggs.

Use in science

“And how many frogs are countless,
They can be counted and counted endlessly, -
They gave frog legs to science,
Hearts were given to science.”
L. Gainulina

Lake frogs are often caught as laboratory animals for scientific, medical and educational institutions.
For example, students of the Orenburg State Pedagogical University use up to 3,000 lake frogs to conduct workshops in physiology and zoology in one year of study.

A lot of biologically active substances have been found in frogs, but they have been studied much less than toads.

It has long been known that if you put a frog in milk, then it will not turn sour for a very long time. Modern research has confirmed the antimicrobial properties of the mucus that covers the skin of the frog. This prevents the reproduction of sour milk bacillus.

It was possible to extract a number of substances with biological activity from the skin of different types of frogs.

Some of these substances are effective in killing bacteria, while others have vasodilating properties. From the skin of the white Australian tree frog, a substance was isolated that has a choleretic effect, as well as stimulating the secretion of gastric juice. From this substance it is possible to make a drug for the treatment of certain mental illnesses.

In the skin of one of the species of frogs, dermorphins were found, which are 11 times more analgesic than morphine.

Frog neurotoxins are among the most powerful. Batrachotoxin, isolated from the Colombian frog, locally called "cocoi", is the most potent of the non-protein poisons, stronger than potassium cyanide. Its action is similar to that of curare.

Substances isolated from some South American tree frogs act on the transmission of nerve impulses in skeletal muscles. Some block smooth muscle receptors, while others cause skeletal and respiratory muscle spasms.

Currently, these substances are not used in medicine, the possibility of including them in clinical practice is being investigated.

The antimicrobial and wound-healing properties of frog caviar have received scientific confirmation - the substance ranidon, which has a high bactericidal activity, has been isolated from the shell of the caviar.

No matter how we feel about frogs, this is one of the most common, frequently used laboratory animals, along with rats and mice. For example, the clawed frog was the first cloned animal, not Dolly the sheep, as we used to think. In the 1960s, the English embryologist Gurdon cloned tadpoles and adult frogs.

For merits in the field of medicine, monuments were erected to the frog in Paris, Tokyo and Boston, as a tribute to and recognition of the truly invaluable merits of these animals in the development of science. So scientists thanked their unwitting helpers in many important scientific research and discoveries. The experiments of the Italian physicists of the XVIII century Luigi Galvani and Alessandro Volta, carried out on frogs, led to the discovery of galvanic current. A huge number of experiments on frogs were carried out by the physiologist Ivan Sechenov. In particular, he used them in the study of the nervous activity of animals. And the frog's heart turned out to be an interesting object for the study of cardiac activity. The French physiologist Claude Bernard, who was also helped to make a number of discoveries by frogs, expressed the idea of ​​erecting a monument to him. And at the end of the 19th century, the first monument to frogs was opened at the Sorbonne (Paris University). And the second was erected by medical students in Tokyo in the 60s of the XX century, when the number of frogs they used for science reached 100 thousand.

In addition to scientific value, these amphibians have practical value. So in many countries, the meat of certain types of frogs is considered a delicacy. There are even special farms where frogs are bred for meat.

Practical work

So, getting started:

07.05.15 caviar was taken in a pond, surrounded by shrubs and aquatic plants.

The shell of each egg is swollen, similar to a gelatinous transparent layer, inside which an egg is visible. The upper half is dark and the lower half is light.

In nature, the rate of development of eggs depends on the temperature of the water. The higher the temperature, the faster the development. In deep, shaded reservoirs, eggs develop approximately four times slower than in well-warmed reservoirs. Caviar easily withstands low temperatures.

We create optimal conditions for the development of caviar: the water temperature is room temperature, warm.

After 8-10 days, tadpoles hatch from the eggs, more like fish fry. Passive, do not feed. Apparently there is enough nutritional reserve of eggs. There are gill openings and gills.

05/23/15 Noticeable metamorphosis. The tadpoles began to feed on their own, move actively, and keep close to each other. They scurry in different directions, but do not swim far, and the whole flock moves almost simultaneously. The average size of tadpoles is approximately 7-8 mm.

By this time, the head, torso, and tail are already visible. The head is large, there are no limbs, the tail section of the body is a fin, there is also a lateral line, and the oral cavity looks like a sucker. The gills are initially external, attach to the gill arches located in the pharynx, and already function as true internal gills.

The suction cup is located below the mouth (it can be used to determine the type of tadpole), after a few days the gap of the mouth along the edges is overgrown with some kind of beak, which works like wire cutters when the tadpole feeds. The tadpole has one circulation and a two-chambered heart.

In terms of body structure, amphibian larvae are close to fish, and adults resemble reptiles.

In nature, sometimes tadpoles form huge clusters - up to 10,000 in one cubic meter of water. Not without reason, among the ancient Egyptians, the image of a tadpole meant the number 100,000, that is, “a lot”. But not all of them survive. The frog larva serves as food for fish, birds, swimming beetles and other inhabitants of the reservoir.

We place tadpoles in different containers:

We place an absolutely transparent plastic container (10 l) in a well-lit area, in a warm place Not in the area of ​​direct sunlight (balcony) - 25 pcs.

We place an absolutely transparent glass container (3 l) in a well-lit area, in a warm place in the area of ​​direct sunlight (balcony) - 10 pcs.

We place a dark, opaque container (5 l) in a warm place, slightly shaded, but with enough light. No direct sunlight (room) - 30 pcs

We place an opaque container (2 l) in a poorly lit, cool place (garage) - 10 pcs.

All containers are filled with water taken from the caviar collection site, i.e. closest to the breeding conditions, as well as algae and grass. Microorganisms are observed in the water.

Within two days, no differences in behavior are observed. All tadpoles are mobile, hiding in mud and grass, and actively react to sound and movement. They feed on plant foods during the day, as if biting off, and also scrape off plaque from the surfaces. Periodically rise to the surface of the water and swallow air. Growth rates are not striking, as you know, they average 0.6 mm per day.

05/25/15 In the glass container, located in the zone of direct sunlight, by the evening all the tadpoles died. At the same time, without preserving the contours of the body, almost completely decomposed and disappeared. Outwardly, the surface of the water in the container looked like it had bubbled up, as if sour.

Conclusion: tadpoles, despite the assertion that complete metamorphosis occurs faster at higher temperatures (21-26 C), and on average it lasts 50-90 days, do not tolerate direct sunlight.

We cover a completely transparent plastic container with paper, protecting it from the sun.

05/28/15 In a plastic container, even though it is not under direct sunlight, the tadpoles are passive, almost without movement. The water is very hot. Several pieces died. Move to a more shady spot.

In other containers, tadpoles are still active. They are in constant motion and feeding.

The growth of tadpoles is already more noticeable. The average is about 10 mm.

We add fresh water and algae from the reservoir, but not from the place of masonry, to all containers with tadpoles.

06/01/15 In a transparent, well-transmitting daylight container, placed in the shade, the tadpoles increased in growth. There was a sharp difference between larger and smaller tadpoles. Large ones are approximately 13-15 mm. They eat all the time, stick to the walls, grab air. The eyes are clearly visible, the marble pattern of the body.

In an opaque container that practically does not let in daylight, but located in a warm place, the growth of tadpoles is practically not noticeable, as well as in a container located in a cool, dark place. Several died, despite the presence of food and the absence of direct sunlight.

Conclusion: there is a high mortality during the developmental period, even in the absence of external predators that feed on tadpoles.

Within 3 weeks with constant feeding and changing the water in containers, because. products of food processing by tadpoles accumulated at the bottom, the death of some specimens and the growth of stronger ones were observed. The average size is already about 20-25 mm.

The highest mortality was in a transparent container located in a warm place. Perhaps from a constant drop in water temperature: from very warm, heated by the sun during the day, to very cold at night.

06/27/15 The tadpole in the garage underwent visible metamorphoses: hind legs appeared.

07/03/15 Within a short period of time, the tadpole takes the form of a small frog. The front legs have grown, the tail has shortened. At the same time, the young frog outwardly turns out to be smaller in size than the tadpole from which it had just formed.

Thus, as in nature, about 2-3 months pass from the moment of laying eggs to the end of the transformation of a tadpole into a frog.

Frog metamorphosis: 1 - eggs (caviar), 2 - tadpole with external gills, 3 - without gills, 4 - with hind legs, 5 - with all legs and tail, 6 - frog.

The most successful of the tadpoles survive to the stage of metamorphosis and turn into a yearling frog. Underyearlings are very voracious. The volume of their stomach in a full state exceeds one fifth of the total weight. There is one interesting detail: if there is not enough animal food in the reservoir, the herbivorous tadpole winters in the larval stage, postponing the transformation from a vegetarian into a predator until spring. They become fully carnivorous once their hind legs develop, feeding on small aquatic animals or even other tadpoles when food is scarce.

07/05/15 As you know, in nature, tadpoles feed on algae, plant matter, and larvae of small microorganisms. In captivity, perhaps due to the lack of plant food (despite its presence in the container), the tadpoles ate the newly formed frog, and not vice versa.

Conclusion

Thus, we conclude that tadpoles are very fragile organisms. Our hypothesis was confirmed.

1. Mortality of eggs and tadpoles reaches 80.4 - 96.8%.

Of the sufficiently large number of hatched tadpoles, 11 survived. At the same time, 5 out of 30 - in a dark, opaque container (5 l), located in a room slightly shaded, without direct sunlight.

3 out of 10 - in a light, opaque container (2 liters), located in a poorly lit, cool place in the garage. At the same time, a frog was formed ahead of all.

Frogs can breed when they reach four years of age. Waking up after hibernation, mature amphibians immediately rush to spawning waters, where they search for a partner that is suitable in size. The male has to perform various kinds of tricks in front of the female in order to get her attention, such as singing and dancing, showing off with might and main. After the female chooses a boyfriend that she likes, they begin to look for a place to lay eggs and fertilize them.

mating games

Voice

Most male toads and frogs attract females of their own species with a voice, namely croaking, which is different for different species: in one species it looks like a “trill” of a cricket, and in another it looks like the usual "qua-qua". You can easily find the voices of males on the Internet. The loud voice on the pond belongs to the males, while the voice of the females is very quiet or absent altogether.

Courtship

• Appearance and coloration.

Males of many species of frogs, for example, tropical poison dart frogs, change their color during mating season, becoming black. In males, unlike females, the eyes are larger, the sense organs are better developed and the brain is enlarged, respectively, and the front paws are decorated with so-called marriage calluses, which are necessary for mating so that the chosen one cannot escape.

• Dance

The attention of females can be attracted and various movements. Colostethus trinitatis just bounce rhythmically on a branch, and Colostethus palmatus get into exquisite poses when they see a female on the horizon, and other species that live near waterfalls manage to wave their paws at females.

Male Colostethus collaris perform a courtship dance. The male crawls up to the female and croaks louder and faster, then crawls away, sways and jumps, while freezing on his hind legs in an upright position. If the female is not impressed by the performance, she raises her head, showing her bright yellow throat, this dares the male. If the female liked the male's dance, then she watches the beautiful dance, crawling to different places in order to better see the male's game.

Sometimes a large audience can gather: one day, while observing Colostethus collaris, scientists counted eighteen females that stared at one male and moved to another position in synchrony. Having danced, the male slowly leaves, while often turning around to make sure that the lady of the heart is following him.

In gold dart frogs, on the contrary, females fight for males. Having found a male who croaks, the female slaps her hind legs on his body and puts her front paws on him, she can also rub her head against the male's chin. The male with less ardor responds in kind, but not always. Many cases have been recorded when this type of amphibian had fights between both females and males for a partner they liked.

Fertilization or how frogs reproduce

Fertilization occurring externally

This type of fertilization occurs most often in frogs. The smaller male tightly clasps the female with his front paws and fertilizes the eggs spawned by the female. The male embraces the female in the amplexus posture, which there are three options.

1. Behind the front paws of the female, the male makes a girth (sharp-faced frogs)
2. The male grabs the female in front of the hind limbs (scaphiopus, spadefoot)
3. There is a girth of the female by the neck (dart frogs).

Fertilization inside

Few poison dart frogs (for example, Dendrobates granuliferus, Dendrobates auratus) are fertilized in a different way: the female and male turn their heads in opposite directions and connect the cloacae. In the same position, fertilization occurs in amphibians of the Nectophrynoides species, which first bear eggs, and then tadpoles in utero until the completion of the metamorphosis process and give birth to fully formed frogs.

Tailed male frogs of the genus Ascaphus truei have a specific reproductive organ.

During the breeding season, males quite often form specific mating rough calluses on their front paws. With the help of these calluses, the male clings to the slippery body of the female. An interesting fact: for example, in the common toad (Bufo bufo), the male climbs on the female far from the reservoir and rides on it for several hundred meters. And some males may ride the female after the mating process is complete, waiting for the female to form a nest and lay eggs in it.

If the mating process takes place in the water, the male can hold the spawned eggs by the female, pressing his hind legs in order to have time to fertilize the eggs (species - Bufo boreas). Quite often, males can mix up and climb on males who clearly do not like it. The “victim” reproduces a specific sound and vibration of the body, namely the back, and forces you to get off yourself. Females also behave at the end of the fertilization process, although sometimes the male himself can release the female when he feels that her abdomen has become soft and empty. Quite often, females actively shake off males who are too lazy to get off, turning over on their side and stretching their hind limbs.

Coition - amplexus

Types of amplexus

Frogs lay eggs, like fish, since caviar (eggs) and embryos lack adaptations for development on land (anamnia). Various types of amphibians lay their eggs in amazing places:

For the entire period of tadpole gestation, which lasts two months, the frog does not eat anything, while remaining active. During this period, she uses only internal stores of glycogen and fat, which is stored in her liver. After the frog's gestation process, the frog's liver decreases in size by a factor of three and there is no fat left on the abdomen under the skin.

After oviposition, most females leave their clutch, as well as spawning waters, and go to their usual habitats.

Eggs are usually surrounded by large gelatinous layer. The shell for eggs plays a big role, since the egg is protected from drying out, from damage, and most importantly, it protects it from being eaten by predators.

After laying, after some time, the shell of the eggs swells and forms into a transparent gelatinous layer, inside which the egg is visible. The upper half of the egg is dark, and the lower half, on the contrary, is light. The dark part heats up more, as it uses the sun's rays more efficiently. In many species of amphibians, clumps of eggs float to the surface of the reservoir, where the water is much warmer.

Low water temperature delays the development of the embryo. If the weather is warm, the egg divides many times and forms into a multicellular embryo. Two weeks later, a tadpole emerges from the egg - a frog larva.

Tadpole and its development

After leaving the spawn tadpole falls into the water. Already after 5 days, having used up the supply of nutrients from the eggs, he will be able to swim and eat on his own. It forms a mouth with horny jaws. The tadpole feeds on protozoan algae and other aquatic microorganisms.

By this time, the body, head, and tail are already visible in tadpoles.

The head of the tadpole is large, there are no limbs, the caudal end of the body plays the role of a fin, a lateral line is also observed, and there is a sucker near the mouth (the genus of the tadpole can be identified by the sucker). Two days later, the gap along the edges of the mouth is overgrown with some semblance of a bird's beak, which acts as a wire cutter when the tadpole feeds. Tadpoles have gills with gill openings. At the beginning of development, they are external, but in the process of development they change and attach to the gill arches, which are located in the pharynx, while already functioning as ordinary internal gills. The tadpole has a two-chambered heart and one circulation.

According to the anatomy, the tadpole at the beginning of development is close to fish, and having matured, it already resembles a reptile species.

After two or three months, the tadpoles grow back, and then the front legs, and the tail first shortens, and then disappears. At the same time, the lungs also develop.. Having formed for breathing on land, the tadpole begins its ascent to the surface of the reservoir to swallow air. Change and growth depend largely on hot weather.

Tadpoles at first feed mainly on food of plant origin, but then gradually move on to food of an animal species. The formed frog can get ashore if it is a terrestrial species, or continue to live in the water if it is an aquatic species. The frogs that have come ashore are underyearlings. Amphibians that lay their eggs on land sometimes proceed to development without the process of metamorphosis, that is, through direct development. The development process takes about two to three months, from the beginning of the laying of eggs to the end of the development of the tadpole into a full-fledged frog.

Amphibious poison dart frogs exhibit interesting behavior. After the tadpoles hatch from eggs, the female on her back, one by one, transfers them to the tops of trees into flower buds, in which water accumulates after rain. Such a kind of pool is a good children's room, where children continue to grow. Their food is unfertilized eggs.

The ability to reproduce in cubs is achieved at about the third year of life.

After the breeding process green frogs stay in the water or keep on the shore near the reservoir, while brown go to land from the reservoir. The behavior of amphibians is largely determined by humidity. In hot, dry weather, brown frogs are mostly unobtrusive, as they hide from the sun's rays. But after sunset, they have hunting time. Since the green frog species lives in or near water, they also hunt during daylight hours.

With the onset of the cold season, brown frogs move to the reservoir. When the water temperature becomes higher than the air temperature, brown and green frogs sink to the bottom of the reservoir for the entire period of winter cold.