撰写Source: Beiqing Net-Beijing Science and Technology News
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A baby elephant in the womb
Scientists found that elephants were originally aquatic creatures, while dolphins were terrestrial animals.
A cell begins to divide, and it embarks on the most dangerous journey of its life. Thomas Hidr Brandt is an American ultrasonic expert in veterinary medicine. Few people in the world can take 4D images of animals in the womb like him. 4D imaging technology is different from ordinary ultrasonic scanning. It can not only produce three-dimensional images, but also capture real-time images to produce 4D dynamic images. For the first time in history, researchers have seen the secret world in the womb of elephants, dogs and dolphins through pictures. Through these images, scientists can even infer whether their ancestors were terrestrial or aquatic.
Elephant sperm is the strongest swimmer.
Elephants are the largest terrestrial animals in the world, and the gestation period is the longest among mammals, reaching 22 months.
Female Asian elephants estrus once every four months, but only two to three days at a time can get pregnant.
When entering estrus, the female elephant will call to the opposite sex, and its low-frequency call can spread to five kilometers away. The strongest male elephant heard the news, defeated other competitors one by one and won the right to mate. Then, the male elephant and the female elephant can spend three days together and mate up to five times a day. Male elephants don’t send their genitals into female elephants. It just shoots a stream of semen at the female elephant’s vaginal opening.
Like the sperm of other mammals, the sperm of male elephants must swim to the eggs of female elephants, but they are faced with a marathon. Male elephant sperm have to swim nearly two meters to find eggs, while human sperm swim eight centimeters is enough.
The female elephant’s vaginal opening is only 2.5 cm in diameter, which is the first arduous challenge for sperm. One third of the sperm will be kept out, and they will be eliminated at this stage. Sperm that successfully pass the customs will also face a fatal threat from the immune system of the female elephant. White blood cells patrol everywhere to prevent foreign bodies from invading. For them, the sperm of the male elephant is the enemy. Thousands of sperm were swallowed and destroyed. The surviving sperm enter the uterus, and the muscles of the uterine wall contract, pushing them towards their destination.
There are also tiny villi on the uterine wall of the female elephant, which will also help the sperm. For sperm, the journey of nearly two meters can be regarded as a long journey, and these hairs provide them with great help. However, there are still many obstacles ahead. Sperm needs to pass through a narrow and winding channel-that is, the fallopian tube connecting the uterus and ovary. Many sperm are defeated at the entrance of the channel.
Scientists believe that once the surviving sperm enter the fallopian tubes, the eggs will secrete some chemicals to attract them. The male elephant shot 5 billion sperm, but by this time only 10 thousand were left.
Twelve hours passed, and the sperm that passed several tests reached the destination-the egg. But here, they have to face the last obstacle: the protective layer wrapped around the egg. In the end, there will be only one sperm, which carries the key mixed protein and can burn through the protective layer of the egg. When the sperm reaches the inner wall of the egg, it will be swallowed by the egg. At this time, the outer membrane of the egg will change immediately, preventing other sperm from entering. Although the fertilized egg weighs less than one thousandth of a gram, the genetic blueprint has been determined, and a five-ton elephant will be born.
The ancestors of elephants may be aquatic mammals, such as manatees or dugongs, and these animals can still be seen in today’s oceans. The elephant trunk began to develop so early, indicating that this organ may have been a breathing tube when the ancestors of elephants still lived in the water. The nose of modern elephants still has the same function. When swimming, elephants can’t breathe through their mouths because their necks are too short, so they stick their trunks out of the water. They can swim for 25 kilometers without rest.
Delayed maturation of canine eggs is related to early wild life habits.
Dogs are one of the most successful species in evolutionary history, which are divided into more than 400 breeds. It is estimated that there are more than 100 million dogs in the world. No other animal has differentiated into so many different species like them. But regardless of size, the gestation period of dogs is about 63 days. The researchers tracked and filmed a golden retriever from conception to delivery. This will be the first time that people will see how the hound fetus grows and develops in the mother’s womb.
Bitches usually ovulate 10 to 12 eggs. Dogs are different from humans, and the eggs discharged from the ovaries are not immediately fertilized. When entering the bitch’s uterus, the egg is not yet mature and ready to accept sperm. But at this time, the bitch has entered estrus.
Male dogs have bones in their genitals, which may make them go smoothly at the beginning of mating. The male genitals may need to be hard enough to enter the female dog at a nearly vertical angle from below. The male dog lay on the back of the female dog and ejaculated after a few seconds.
At this time, the two of them entered the locking stage. With the contraction of vaginal muscles, the male dog’s genitals are firmly stuck in the female dog. During this time, the male dog’s prostate secretes more fluid to transport sperm. The locked state can last for 5 to 60 minutes.
At this time, the sperm is rushing to the egg. However, the egg is not yet fully mature. At this time, the sperm that comes into contact with the egg cannot fertilize it. It will take another two days for the eggs to be ready.
All the other females excrete mature eggs, and if they are not fertilized within a few hours, they will rapidly decline. Experts believe that the delayed maturation of canine eggs may be caused by early living habits in the wild. It may not be easy for females in wild dogs to find mating partners, so the longer the eggs survive, the higher the chances of successful fertilization when they have the opportunity to mate. It is precisely because of this that the sperm of domestic dogs will attach to the tube wall and wait after entering the fallopian tube.
Sperm can live here for 7 days, sometimes even as long as 12 days. When the egg is ready for fertilization, the sperm will leave the tube wall and continue to swim to the egg. One consequence of delayed fertilization is that puppies born of the same fetus may have different fathers.
The fertilized egg goes to the uterus. In just 63 days, each cell group will become a puppy.
Dolphins can mate 365 days a year.
Dolphins have beautiful streamlined bodies, but their ancestors may have walked on land.
Dolphins and humans have the same important feature: their sexual behavior is not just for reproduction. For dolphins, this is a way for group members to enhance their feelings. Therefore, although female dolphins only ovulate two to seven times a year, they can mate 365 days a year. Dolphins tease and love each other for a long time, but the actual sexual behavior only lasts for a few seconds. It is dangerous to be so selfless at sea.
Seawater will kill sperm. In order to protect sperm, female dolphins will tightly stick to the genitals of male dolphins, so as not to drop water. When male dolphins ejaculate, they excrete a lot of semen, nearly 80 ml at a time. The sperm content of most semen is very low, which may be just to wash away the sperm left by the previous male dolphin. However, the concentration of this part of semen reaching the target is very high, containing about 300 million sperm per milliliter. This concentration is at least 15 times that of healthy male semen.
Recent studies have shown that when male dolphins pull out their genitals, they will trigger a series of contraction reactions of female dolphins. At this time, sperm is passing through a passage called pseudocervix. There is a circle of muscle around the channel, and the sperm will contract after passing through. This method can effectively prevent seawater from entering dolphin cervix. After fertilization, it takes a year for this small group of cells to develop into a small dolphin.
In the third week of pregnancy, the whole embryo is less than 1.5 cm long. After 24 days, a strange phenomenon appeared. Although flippers have begun to grow at the bottom of the embryo, legs like limb buds have also appeared.
After these little limbs grow out, they gradually shrink in the next two weeks until they disappear completely. However, why do they appear in the early stage of development? Scientists believe that this is the evidence that dolphins were once terrestrial animals.
Editor: zhangxin