The development of a frog from spawn to individual in an unnatural habitat under different environmental conditions. From egg to frog

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 the 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.

After hibernation, frogs and toads go to shallow ponds, ditches, puddles and meltwater spills well warmed up by the sun. Here, the females spawn, very similar to fish eggs, and the males pour seminal fluid over it.

Caviar, as a rule, is laid a lot, with a margin, because from the stage of fertilization to the adult frog, countless dangers lie in wait for their offspring. Unfertilized eggs become white or opaque. If everything went well, you can observe the division of the yolk into two, then into four, into eight, and so on, until it looks like a raspberry inside the jelly. Soon the embryo begins to look more and more like a tadpole, moving little by little inside the egg.
On average, the egg stage lasts about 6-21 days, until the time when the larva hatches out. Most eggs develop in calm or stagnant waters to prevent mechanical damage to the eggs.

Tadpole

Immediately after hatching, the tadpole feeds on the remains of the yolk, which is located in its intestines. At the moment, the amphibian larva has poorly developed gills, mouth and tail. This is a rather fragile creature. The tadpole initially attaches itself to objects in the water using small, sticky organs between its mouth and abdomen.

Then, 7-10 days after the tadpole has already hatched, it will begin to swim and feed on algae.

After 4 weeks, the gills begin to overgrow with skin until they eventually disappear.
Tadpoles get tiny teeth that help them scrape off algae. They have long had a spiral-shaped intestine, which makes it possible to extract the maximum amount of nutrients from the food they eat. At this time, the tadpole has a developed notochord, a two-chambered heart, and one circle of blood circulation.
Interestingly, by the fourth week, tadpoles can be considered quite social creatures. Some are even able to interact with each other like fish!

Tadpole with legs

After about 6-9 weeks, the tadpole develops tiny legs and begins to grow. The head becomes more pronounced and the body lengthens. Now large objects, such as dead insects or plants, can also serve as food for the tadpole.

The forelimbs appear later than the hind limbs, with the elbow being detected first.

After 9 weeks, the tadpole looks more like a small frog with a very long tail. The process of metamorphosis begins.

By the end of 12 weeks, the tail gradually disappears and the tadpole looks just like a miniature version of an adult frog. He soon emerges from the water to begin his adult life. And after 3 years, the young frog will be able to participate in the process of reproduction.

Some frogs that live at higher altitudes or in colder places may take much longer to go through the tadpole stage. Others exhibit unique developmental stages that differ from the traditional tadpole-in-water life cycle type.

Is the life cycle of a toad and a frog different?

In fact, toads are the same frogs. Toads are just called differently, look a little different, but they are all part of the frog family. Many people are wondering what is the difference between the life cycle of toads and frogs. Perhaps the main difference will be that frog caviar looks like clots, and toad caviar looks like ribbons or stripes.

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, 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 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 a 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 reserves of yolk. 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.

Among many animals, only the so-called invertebrates reproduce asexually. Vertebrate animals - such as mammals, fish, reptiles, birds and amphibians - reproduce sexually: spermatozoa and eggs, which carry hereditary material typical for this species, are combined during fertilization. A fertilized egg is called an embryo.

Depending on the type of animal, the embryo can develop both in the mother's body and outside it. Gradually, little cubs develop from fertilized eggs in accordance with the genetic guidelines laid down in it. Many, like frogs, go through another developmental stage before becoming fully grown.

From egg through larva to adult

Snails live on land, in running water and in the seas. Sea slugs lay their eggs in sea water, which, after high tide, get stuck between the rocks. The fertilized eggs hatch into larvae (veligers) that can swim. They swim with the current and finally sink to the rocky bottom, where they turn into adult crawling clams.

fertilized egg

The red dot in the middle of the egg yolk is a three-day-old chicken embryo. A week later, the embryo already takes the form of a chicken. A month later, the chick is already fully developed and covered with soft fluff. With an egg tooth on his beak, he breaks the egg shell and comes out into the light. The chick is hatched and becomes an adult without any additional developmental stage.

From egg to tadpole

During the mating season, many frogs gather in large noisy groups. Females respond to loud calls from males. Only a few species of frogs give birth to live young; most species lay their eggs (spawn) in or near water. The number of eggs depends on the type of frog and ranges from one to twenty-five thousand. As a rule, the eggs are fertilized outside the body of the frog and left to their own devices. When the egg matures, a small tadpole hatches from it. Tadpoles live in water and breathe through gills like fish. Only in a few species of frogs do females take care of their offspring.

Frogs and toads

Unlike adult frogs, tadpoles are herbivorous and feed on aquatic plants and algae. After a certain time, an amazing transformation (metamorphosis) occurs in the development of the tadpole: the fore and hind limbs appear, the tail disappears, the lungs and eyelids develop, as well as a new digestive system designed to digest animal food.

The rate of transformation is different in different species, the main factor here is the temperature of the water. In some toads and frogs, metamorphosis occurs in a few days or weeks, while in others it takes several months. The tadpole of the North American bullfrog does not fully develop until after a year or more.

Frogs and toads belong to the class of amphibians and to the same group of anurans, but differ in appearance and lifestyle. Frogs have soft skin and are good jumpers, while toads are covered in warts and tend to crawl. There are over 3,500 species of frogs and toads on earth. With the exception of Antarctica, they can be found on every continent. They prefer to live in tropical and subtropical zones, where more than 80% of all species live. But wherever they live, in deserts or mountains, savannahs or tropical rainforests, they must return to the water in order to procreate.

What is metamorphosis

In their development, frogs go through three stages: from an egg to a tadpole, and then to an adult frog. This process of development is called metamorphosis. Many invertebrates also pass through the stage of larvae in their development. However, the most amazing changes occur in the life of insects: butterflies and beetles, flies and wasps. Their life is divided into four stages, very different from each other in terms of feeding and habitat: egg, larva, pupa, adult insect. The larva looks completely different from the adult insect and has no wings. Her life is completely focused on growth and development, and not on procreation. Only after the larva pupates does it become an adult insect.