After hibernation frogs and toads go to shallow ponds, ditches, puddles and floods of melt water 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. On the this 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. Soon he's out of the water to start 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.
The lesson allows you to repeat and expand children's ideas about amphibians and their habitats, enrich knowledge with new information about the life of frogs, teaches you to speak out, brings up a careful and environmentally competent attitude towards animals.
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Summary of the lesson for children of the preparatory group
"HOW A TADpole TURNS INTO A FROG"
Main educational area: "Knowledge"
Target: To arouse in children an interest in objects of wildlife, to form their ideas about the stages of development of some animals.
Equipment, materials, tools:Audio recording of frogs croaking, figurines of toy frogs, pictures depicting the stages of development of a frog (roe-embryo - a tadpole without legs - a tadpole with two legs, a tadpole with four legs and a tail - an adult frog)
Lesson progress:
The teacher makes a riddle:
Shiny, eyed,
Lives in the lake, swims on the water.
Sitting on the shore, looking at the mosquitoes.
Green frog - big-eyed ...
Children answer: frog
Educator: Children, do you know how frogs “talk”?
After the children's answers, the teacher gives an audio recording with the voices of frogs and shows figurines of toy frogs.
Then he shows a picture of tadpoles and asks the children if they know who is in the picture and explains that this creature is called a tadpole because it has a big head.
The teacher explains that frogs in childhood are not very similar to adult frogs and invites children to determine how a tadpole is, and what is not, like an adult frog.
Then he invites the children to listen to a story about how frogs are born, which is accompanied by showing pictures and depicting the stages of frog development:
In one quiet transparent lake lived a large green frog. She really wanted to have baby frogs. Once spring came, the frog laid small transparent balls - eggs on the shore of the lake. After some time, creatures with a small body, a large head and tail appeared from the eggs. At first, the frog didn’t even like it, because they didn’t look very much like their mother. After all, the frog itself did not have a tail, and the head was not so big, and most importantly, it had four legs. The tadpoles swam, ate and grew. Some time passed, and they first had hind legs, and then front legs. Now they have already become more like an adult frog, although they were still tadpoles with tails. Their mother could not wait until the tadpoles finally turn into real frogs. But such a moment has come: the tadpoles have grown and become beautiful, green frogs with four legs without tails. In the evenings, they croaked with their mother, who was very proud of them.
After the story, the teacher discusses with the children how to arrange the cards depicting the developmental stage of the frog so that they reflect what happened in the story. In conclusion, he emphasizes that frogs grow from tadpoles, which in turn emerge from eggs.
It is in spring, in lakes, ponds, puddles, that you can see sticky, transparent balls with a black dot - frog eggs. At the end of the lesson, he invites the children to show how frogs jump, croak, how tadpoles swim.
The frog turns into a prince only in a fairy tale. But don't the transformations that a frog undergoes during its life cycle demonstrate evolution? From a tadpole resembling a fish (even having gills), the “frog cub” quickly “transforms” into a completely new form to start leading a radical new lifestyle! The mouth becomes wider, the tail dissolves, but an "elastic" tongue is formed for catching flies, and nostrils appear, and bulging eyes move to another place on the head. Finally, when the lungs finally mature and four legs grow, this matured tadpole celebrates its “coming of age” by jumping out of the water to now live on land.
This amazing transformation (metamorphosis) is far from being just external. Almost all organs and systems of the body undergo a radical restructuring. For example, a complete reconfiguration of the nervous system is needed to control new or reprogrammed organs - eyes, ears, paws, tongue, etc. A similar reorganization must also take place at the biochemical level. Changes in hemoglobin in the blood, light-sensitive pigment in the eyes, among many other changes. Even the excretory (excretory) system of the frog is changing in order to fit the new way of life.
Biologists are puzzling over the mega-complexity of this "rebirth" that occurs in ordinary ponds. A frog basking on a water lily leaf is an amazing result of many changes occurring sequentially with amazing accuracy in the right order. It would not be an exaggeration to say that the opening ceremony of the Olympic Games simply pales in comparison to the "choreography" of the frog's metamorphosis process. The life of a tadpole would certainly become more difficult if, for example, its tail disappeared before the legs grew. The same applies to his internal organs, bones, nervous system, biochemical processes, etc. Any failure can stall the entire process of reorganization of the organism ... and lead to rather unfortunate results (for a tadpole)!
photolibrary.com
Very difficult program
The fantastically complex information encoded in the DNA that allows a tadpole to turn into a frog clearly points to the Higher Intelligence that created it. Such a program cannot be formed in a natural way - it demonstrates the originally intended end result.
All steps are interconnected
Years of research have uncovered several levels of processes required to effect this "transformation of life." For example, the disappearance of the tail requires a precisely programmed execution of micrologistics operations. First, the tadpole stops the formation of tail muscle cells. It then produces a series of highly specific enzymes that dissolve tail cells.
Then, at the right moment, these "little killers" are combined and injected into tail cells of all types. Finally, roaming macrophages engulf these dead cells to then reuse their components and nutrients elsewhere in the body (i.e., the tail is not shed, but reabsorbed by the body).
"Change" does not mean "evolve"
So how justified is the assertion that this is an example of " evolution in action"? Is the transformation of a tadpole into a frog a good example of evolution?
Quite the opposite! Although the tadpole may look like a real "fish" in appearance, it is a frog from its very birth. Everything that he needs for rebirth (that is, all genetic information, schemes and programs) is already embedded in the DNA code stored in the nuclei of the tadpole's cells. At this micro level, we find not only a complete plan for the development of a frog, but also a fully functional factory with all the necessary mechanisms and equipment to bring this plan to life.
The genome of a fish does not contain the information needed to become an amphibian, and there is nowhere for it to get such information from.
This embedded information is the key difference between the evolutionary tale (as if a fish evolved into an amphibian) and the real world (in which a tadpole turns into a frog). From the very moment of its birth from an egg, the tadpole is already equipped with a complete set of instructions "how to turn into a frog on your own." In contrast, fish only contain the genetic instructions for "building"... fish! The genome of a fish does not contain the information needed to become an amphibian, and there is nowhere for it to get such information from. In fact, it is doubtful that there is even one undisputed example of how evolutionary mechanisms have contributed new information into the genetic blueprint of any being.
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 a croak, which different types different: 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.
- Behind the front paws of the female, the male makes a girth (sharp-faced frogs)
- The male grabs the female in front of the hind limbs (scaphiopus, spadefoot)
- 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. Interesting fact: for example, in the common toad (Bufo bufo), the male climbs on the female far from the reservoir and rides on her 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.
