1. The reasons for the diversity of parental behavior. Amazing diversity of parental behavior is demonstrated by amphibians. In this ancient group of animals living both in water and on land, almost all possible methods of reproduction are described, from external fertilization and laying a huge number of eggs simply in water bodies to internal fertilization and live birth, accompanied by the formation of an analog of the mother's placenta. Moreover, it is interesting that in different amphibian families all methods of reproduction and parental behavior can be observed, regardless of the living conditions of the species. Such diversity is demonstrated, for example, by the oldest legless amphibian worms. The only thing that is not observed in amphibians is the cultivation of offspring in complex family groups. Evolutionary scientists jokingly argue that amphibians are a kind of testing ground on which nature experimented, creating ways to reproduce higher vertebrates. It should also be noted that the males take care of the offspring of this phenomenal group with rare exceptions.
2. Features of the reproduction of amphibians. Most species of amphibians live on land, and breed in fresh water. Amphibian life is significantly dependent on temperature and humidity.
After hibernation, all amphibians of the middle band accumulate in fresh water. Soon, females begin to lay eggs. Some of them, such as brown frogs, lay eggs near the shore of the reservoir - in small, warm areas. Others, such as green frogs, lay eggs at greater depths, most often among aquatic plants. In frogs, eggs stick together in large lumps, in toads - in long cords. Tritons place single eggs on the leaves or stems of aquatic plants. Fertilization in most amphibians is external. In this case, males release sperm fluid into the water. After fertilization, embryos develop in the eggs and the larvae hatch soon. Amphibian larvae are real aquatic animals breathing with gills. During the transition from an aquatic, larval lifestyle to a terrestrial, “adult” one, a complex process of transformation of various organs — metamorphosis — occurs in the larva's body. It is interesting to note that in some amphibians leading an aquatic image, the phenomenon of neoteny is observed, i.e. ability to reproduce in a larval state. An example of this is the widespread aquarium animal - axolotl.
3. Types of care for offspring in amphibians. Most of the amphibian laying eggs does not exhibit any behavior related to the care of the offspring, and after laying eggs leaves the water bodies, leaving their offspring to their fate.
However, for example, a bull frog that lives on the islands of the Caribbean has been protecting eggs and larvae emerging from it for a long time. Moreover, the male monitors the water level in the drying puddles in which they develop, and, if necessary, deepens the puddles or digs a groove in an adjacent puddle, through which then tadpoles are driven into it.
Various types of parental behavior are observed in tree frogs. Living in the crowns of tropical forests, many tree frogs are faced with the problem of finding water for their offspring. Therefore, among the representatives of this family there are those who have developed very interesting forms of care for offspring. In some species, parents build special nests on plants that replace water bodies with larvae; in others, they build artificial water bodies; in others, they carry eggs and larvae on themselves. So, tropical leaf-tree frogs lay eggs on the leaves of trees and protect the clutch until the larvae hatch. Tadpoles hatching from eggs crawl onto the wet back of the male, and he one at a time transfers them to the microarrays located right on the trees, in the axils of the leaves. In the absence of suitable water bodies, the tadpoles remain on the back of the male throughout the entire period of metamorphosis. He periodically bathes with them in larger puddles. In some leaf climbers, males constantly transfer tadpoles from one bath to another so that they, having eaten all the food in a small pond, do not starve. In one species of leaf climbers, a female carries tadpoles into water bodies located at the base of the leaves. Then she regularly visits the cubs and lays several unfertilized eggs in the water, which serve as food for the tadpoles.
Very caring fathers are males of a purely land European midwife toad. Females of this species of toads lay eggs on land in the form of two cords containing 20-50 eggs. The male helps the female to free herself from them. Grasping the cords with the fingers of his hind legs, he pulls them out and wraps himself. An active male can get eggs from two or three females in this way. During the entire period of development of the caviar, which lasts several weeks, the male wears the cords on himself. At the end of this period, the male goes in search of a reservoir, where the larvae hatch. After that, he is freed from the empty cords.
4. Brood bags of amphibians. Some species of frogs carry eggs and larvae in special brood bags. During the breeding season, the skin that forms the bag changes its structure. Poison glands, pigment cells disappear from it, keratin resolves. It becomes tender and enriched with blood vessels. In Australian marsupial tree frogs, pockets are located in the groin area of males. The development of eggs takes place on the ground, and the larvae emerging from it creep into their parents' bags. A large yolk sac provides them with sufficient nutrition and allows them to stay in brood bags until metamorphosis. In some species, a bag, like a backpack, is located on the back or on the stomach.
A male Darwin, a tiny water frog of a rhinoderm, carries eggs in his throat sac. The larvae hatched from the egg are first provided with a yolk sac with a substantial supply of food. During this period they can move freely. After depletion of the embryonic supply of food, the larvae grow back and tail to the wall of the throat sac. As a result, two layers of larvae are formed inside the bag, with their abdomen lying on top of each other, their skin on the back and tail has a special structure that allows them to extract oxygen and necessary for development from the father’s blood. Packed like cigarettes in a pack, they spend their adolescent rhinoderm tadpoles. When the metamorphosis ends and a complete reduction of the tail occurs, the children lose contact with the parent body. They no longer need paternal support, and the frogs leave his mouth. After this, the father’s throat sac gradually returns to normal, and the male regains the ability to eat normally. In another species of frogs, which is systematically close to the rhinoderm, a similar process occurs in the male’s stomach. In this case, the developing frogs receive additional and necessary nutrients for metamorphosis due to the resorption of part of the larvae.
In these cases, we also, like what is observed with a seahorse, are dealing with a partial reversal of the floor. However, in amphibians, the process goes even further and the brood sac of the rhinoderm already represents a complete similarity to the placenta of mammals, which was formed contrary to all the rules in the male body.
Chemical composition of water
For amphibians, even the level of oxygen in the water is important. When amphibian is in water saturated with gas, it can suffer from the so-called "bubble disease" or "bloating". Bubbles of oxygen enter the bloodstream and, if they are large, they can block part of the circulatory system. Symptoms of this disease are not apparent. Unless the animal becomes lethargic. Internal bleeding is difficult to detect by visual inspection. In frogs, air bubbles can be seen in the membranes between the fingers, in eastern newts in the eyes. Also, bloating can result from bloating. Air bubbles can damage the blood circulation system, causing the penetration of various bacterial infections.
Tanzanian Arboretum (Leptopelis vermiculatus)
If "vesicle disease" is diagnosed, the animal must immediately be transplanted into water with normal oxygen levels. In case of circulatory disorders and tissue necrosis, antibiotic treatment can help, but only if the disease has not gone very far.
An increased gas content in water may occur in the following cases. Naturally, this occurs in well water when it is heated during the summer months. The activity of microorganisms can also change the gas level.
Amphibians sent by air in an unpressurized compartment (all commercial airlines have airtight compartments) may also manifest this condition.
It is very difficult to measure the level of water supersaturation with oxygen and lower it.
It is best to pass water through a tube having a large surface area, but without air. The easiest and cheapest way is to simply pour water into a vessel and let it stand for a couple of days. The gas will go into the atmosphere and the water will be ready for use.
Credit: Portal Zooclub
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