In daily life, flies are a kind of annoying insects, and its weariness is everywhere. There are traces of flies in all areas related to human activities. In the 1950s, flies were listed as “one of the four pests”, and there was a nationwide campaign to eliminate the four pests. Even so, flies were still not completely eliminated. It seems that it is always coveting to blend into human life, and it is a population that human beings can never accept.
During the evolution of Drosophila, the length of sperm can reach 20 times of body length
Every summer is the season of flies, which has a great impact on human life and threatens human health. In biology, flies are typical “completely abnormal insects”. There are more than 4200 kinds of flies. The common flies are housefly, City fly, green bean fly, fruit fly and so on. Compared with other flies, fruit flies are very small, so they can enter the house through the cracks around the doors and windows. After entering the house, Drosophila will breed quickly. Before being found, a team of Drosophila has begun to take shape to carry out indoor activities.
The life cycle of fruit flies is very short. It takes only eight days from egg to adult, which means that if the flies are not eliminated in the room within a week, it will nourish a small population of fruit flies. The female flies can live for about one month at most, but in such a short time, they can lay 500 eggs.
However, it is worth mentioning that there was a paper published in the Science Journal of nature, which described in detail the changes of spermatogenesis in the evolution process of male Drosophila bifida. Now we see male Drosophila, its sperm length has reached 6 cm, which is 20 times of the body length. The sperm length of male Drosophila melanogaster is the highest in the family of flies. Although the sperm of male Drosophila melanogaster is very long, it also has a disadvantage, that is, the longer the sperm is produced, the less the number will be. In order to improve the chance of pregnancy and reproduction, male Drosophila can only increase the mating frequency. The more mating times, the more advantage the long sperm entering the reproductive tract has. It can directly crowd out other short competitors. In the long-term evolution process, the sperm development of Drosophila becomes longer and longer, and produces more offspring as far as possible.
The paradox of giant sperm: female sexual selection promotes sperm evolution
Under normal circumstances, a female fruit fly will mate with many male fruit flies. From the evolutionary point of view, the more sperm produced by male organisms, the more conducive to reproduction. However, contrary to this, male Drosophila did not produce a large number of sperm in the process of evolution, but spent a lot of energy to produce the longest giant sperm, which was longer than the length of male Drosophila. Therefore, some people think that this is a paradox of giant sperm. So how to explain the situation of fruit flies?
Scott pitnick of Syracuse University in New York offers a possible explanation for the paradox of giant sperm in fruit flies. The results were published in the journal Nature. Pitnick believes that the giant sperm length of male Drosophila is directly related to the sexual selection of female Drosophila. In other words, sexual selection in females drives sperm evolution in males. For example, female flies like to prefer the length of sperm, so according to the preference of female flies, the sperm length of male flies will become longer in the process of evolution. Of course, this sperm length is directly related to the strength of male Drosophila. If male Drosophila is very weak, it is impossible to produce this kind of giant sperm. After all, producing giant long sperm also requires a lot of energy. Without strong energy in the body, it is impossible to complete this work.
In addition, pitnick thought that there should be spermatozoa in female Drosophila, which could be preserved for a long time. For example, when the female flies want to fertilize, they will take out their sperm to complete fertilization. Whether the male flies can complete the task of reproduction depends entirely on the “mood” of the female flies. At this time, the longer the length of spermatozoa in the seminal vesicle of female Drosophila melanogaster, the more advantage it will have. It can squeeze out other short spermatozoa anytime and anywhere, so that it has more chances to be preserved. It can be seen that there are two stages in the process of reproduction between female Drosophila and male Drosophila. One is to let male Drosophila transport sperm to the seminal vesicle first, and the other is to complete the fertilization process by themselves. Female Drosophila can control their offspring anytime and anywhere.
What are the advantages of giant sperm of Drosophila? Why did they evolve giant sperm?
As we all know, sperm is the reproductive cell of male animals. As far as human beings are concerned, the sperm length of an adult male who is more than 1.7 meters tall is only about 50 microns. Only under the microscope can we see that the larger the size of animals in nature, such as elephants or whales, the smaller their sperm size will be. So in our known species, the sperm length of male Drosophila is larger than its body length. What are the advantages of this giant sperm for Drosophila? Why do fruit flies evolve giant sperm?
1. Female Drosophila is more picky: in the process of sexual selection, long sperm is dominant
Scientists have found that the sperm characteristics of different male fruit flies are also different. Female Drosophila is more picky. In terms of sexual selection, female Drosophila promotes the evolution of sperm in male Drosophila. Generally speaking, female fruit flies prefer longer sperm. For male fruit flies, if they want to produce this kind of huge sperm, they need to have a strong body. After all, this kind of huge sperm needs more energy to produce. However, the longer the sperm is, the less the number will be. In order to make their offspring reproduce better, male fruit flies can only improve their mating ability So the reason why male Drosophila can evolve huge sperm is that female Drosophila promotes sexual evolution.
2. The giant sperm produced by male flies can avoid being eaten by female flies
When Drosophila is in a bad ecological environment, in the face of lack of water and food, female Drosophila will benefit from the semen of male Drosophila. Because the genitals of male Drosophila are wrapped outside, female Drosophila can control the situation and gobble up the semen. It is worth mentioning that not all semen will be taken out of the body by female Drosophila, for example, some long sperm will escape If not eaten, the short sperm will be the best energy for the female to replenish her body. Therefore, in general, the giant sperm in male Drosophila melanogaster has a very strong advantage and will not be the “liquid” energy supplement for female Drosophila melanogaster.
3. It can promote the evolution of male sperm length to a longer direction
The more picky the female is about sperm, the easier it is for the male to evolve in a longer direction. In other words, in the process of evolution, the higher the quality and the longer the length of sperm, the more likely it is to be loved by female Drosophila, and they can benefit from it and reproduce better. For any mother, they want to be able to breed a better life. However, this breeding process is inseparable from strong genetic inheritance, so female Drosophila will choose the male with strong physique and longer sperm to complete the mating process.
4. The long sperm produced by male Drosophila can squeeze out the short sperm and be preserved
As we have mentioned earlier, there is a special organ in female Drosophila melanogaster, the spermatophore organ, which is specially responsible for storing sperm. Female sperm can control the time and place of fertilization at will, so the longer the sperm is, the easier it is to be preserved. On the contrary, the short sperm in the spermatophore is easy to be excreted by the long sperm, For male fruit flies, the longer the sperm, the greater the chance of reproduction.
The smaller the mammal, the larger the sperm
In nature, the length of sperm of different organisms will vary greatly. For example, the sperm of wild boar is very small, while the sperm of Drosophila is 20 times of its size and length. As we all know, the larger the size of the sperm, the faster it will swim and better combine with the egg. In the process of spermatogenesis of different species, the number of spermatozoa increases with the increase of chromosome exchange. Chromosome exchange increases the possibility of genetic variation and is an essential “raw material” for natural selection.
In mammals, the size of the whale is more than 30 meters, but the sperm produced by it is not as long as that produced by mice. Therefore, in the process of mating, the shorter the sperm is, the more difficult it is to enter the female reproductive tract and combine with the egg. The time and “distance” that blue whale sperm takes to combine with the egg is 100 times that of mice. For male species, “fish and bear paw can’t have it both.” male fruit flies produce huge sperm, so the number will become relatively small. After all, the body needs a high cost to produce sperm, and the energy in the body is limited. Sperm evolution of species changes with the preference of female species. Once fruit flies are found in the room, we must take immediate action to eliminate them.
In nature, it’s amazing for mammals to complete the exchange process, but many people like to eat animal’s “sexual organs”. In addition to running on the ground, there are also swimming in the sea. Of course, compared with swimming in the sea, the “genital food” is relatively more expensive. For example, puffer fish and COD testis in Japanese cuisine, sheep whip in barbecue ingredients, and chicken rump tip in Fried String. Human beings use animal genitals as nourishing food. However, these genitals are more likely to gather harmful toxins such as heavy metals and organic pollutants. Excessive consumption of high cholesterol sexual organs is harmful to human beings, so we should pay more attention to them We should respect the nature, not let all wild animals become delicious food on the table, which is also a kind of harm to human beings. After all, all the germs are imported from the mouth, refuse game, start from you and me!