Why do tadpoles turn green when they turn black into frogs?

Darwin's theory of evolution points out the survival of the fittest? . In the process of long-term evolution, frogs have different colors, but frogs of other colors are easily found by their natural enemies and eaten. Only green frogs are preserved because their colors are similar to those of vegetables, so they are not easy to be found by natural enemies. Most of the young frogs they gave birth to are green, and they are eaten by natural enemies. After many generations of elimination, those who are not green are eliminated.

Extended information

Frog belongs to Chordata, Amphibia, Anura and Ranidae. The adult has no tail, eggs are laid in water, fertilized in vitro, hatched into tadpoles, and breathed through gills. After mutation, the adult mainly breathes with lungs and skin. Most frogs reproduce by in vitro fertilization, and fertilized eggs hatch outside the mother's body into tadpoles. Only 1 to 12 species of frogs in the world have evolved to fertilize in vivo, and some of them will excrete fertilized eggs and hatch into tadpoles. But in zoology, frog refers specifically to the black-spotted lateral fold frog. Frogs have always been regarded as oviparous animals, but scientists have found that a frog living in the rainforest of Sulawesi, Indonesia can give birth to tadpoles. This frog is the only frog among more than 6, kinds of frogs in the world that can "drop tadpoles".

Frogs are slim and good at swimming. The neck is not obvious and there are no ribs. The ulna and radius of the forelimb healed, and the tibia and fibula of the hind limb healed, so the claw could not rotate flexibly, but the limbs were muscular. The most primitive frogs began to evolve in the early Triassic. The earliest frog with jumping action appeared in Jurassic. Because frogs feed on insects and other invertebrates, they must live by the water. There are about 13 species of frogs in China, and almost all of them are experts in killing pests in forests and farmland.

Frogs often inhabit rivers, ponds, rice fields and other places, mainly moving in the grass near the water, and sometimes lurking in the water. Most of them are active at night, mainly eating insects, and also eating some snails, snails, shrimps, small fish and so on. Most of the insects they eat are agricultural pests. It is estimated that a frog can prey on 7 insects a day and kill 15 pests a year. Therefore, frogs are beneficial to agriculture and should be protected. When the weather gets cold in late autumn, frogs hibernate in the bottom of the water or in caves, and then return to the water to breed when the weather gets warm in the following spring. During the breeding period, many male frogs often gather in the same area and sing loudly and continuously. This is the so-called "frog quarrel pit".

In fact, this is a courtship behavior of male frogs, which attracts the opposite sex by chirping and forms a spouse. After mating, the female frog begins to ovulate in the water, with about 3,-6, eggs each time. At the same time, the male frog excretes sperm into the water. Sperm and egg cells combine in water to form fertilized eggs, which develop into tadpoles after 4-5 days of incubation. Tadpoles must live in water, swim with their tails, breathe with their gills, and eat plant foods such as diatoms and green algae. After two months of development, tadpoles metamorphosed into young frogs, their tails gradually disappeared, their body length was greatly shortened, and they began to live on land, and their feeding habits began to change to animal-based foods. It takes about three years from young frog to sexual maturity.

Reference: Frog-Baidu Encyclopedia.