This article is from WeChat official account:Science University (ID: kexuedayuan) , author: Lee ink spilled, the original title: “stuck on the table, in the wild strike out” from the title figure: vision China
Speaking of crayfish, everyone’s first impression should be the tempting delicacy in the food stalls on summer nights, the spicy taste of the beating tongue, and an indispensable foil when talking about the world.
But in fact, it is also an invasive creature that causes a serious ecological crisis. The lively discussion among netizens happened to be the manifestation of two completely different identities of crayfish in the eyes of human beings.
Some netizens believe that in China, the “crayfish” invasion is equivalent to “self-investment”, just waiting for it to be sent to the supper: “If the crayfish is in a foreign country, it can be regarded as flooding. In the country, It’s called a harvest at best.” Some netizens believe that the prevention and control of crayfish does not conflict with food and breeding: “Wild crayfish and eating are two different things.”
In addition, news of hairy crabs invading Germany has also set off a wave of discussions on the Internet. Many netizens expressed their willingness to carry forward the spirit of internationalism, but there is still no lack of “I advise you to be more clear”. It seems that the crayfish and hairy crabs on the table are completely different from the crayfish and hairy crabs that fight hard on the table.
So what is the true face of crayfish? What about hairy crabs?
Crayfish: I have been waiting for you in Tarim, Xinjiang
The “little lobster” known by people in the rivers and lakes, the official Chinese name is Procambarus clarkii(Procambarus clarkii), which is native to the United States, In the late 1920s, it was introduced from Japan to Nanjing, my country, and started breeding. Crayfish is not reconciled to being imprisoned, ready to change the story for himself, try to be the protagonist.
In the new plot, the crayfish is transformed into a powerful dragon because of poor management of the farm, and successfully escaped from the “darkness” farm and entered the rivers and lakes of our country. Easy to feed, grow faster, and give birth to more. Crayfish have everything they call invasive creatures.Favorable conditions, so they soon established a natural breeding population in the wild, and the shrimp thrived from then on.
The crayfish have never stopped traveling far, and their distribution has gradually spread along the Yangtze and Huaihe Rivers to Anhui, Hubei, Hunan, Jiangxi, Shanghai, Zhejiang, Guangdong and other provinces and cities. Some of these proliferations are purely man-made disasters. For example, in 2000, someone from Kunming brought crayfish back to farming and lost some in Dianchi Lake.
Six years later, crayfish have spread throughout Dianchi Lake. Due to its strong adaptability, even in the Tarim River Basin of Xinjiang in the northwest region, crayfish farming has been developed in recent years. China’s largest inland river, there may also be escaped crayfish.
The crayfish are living a good life, but the native animals and plants are suffering-the outbreak of crayfish will eat a lot of chara, myriophyllum and other plants, not only causing serious damage to the plants in the waters , And also plundered food from other native animals. In addition, crayfish also changed the community structure of animals and plants, making the living environment quality of organisms deteriorate, and clear lakes gradually became muddy.
According to this, the “List of Invasive Alien Species in Yunnan Province” released in 2019 classified invasive species in a more detailed manner, from the highest level I “malignant invasive” to the lowest level V “to be seen” It is divided into five major categories. Crayfish ranks Ⅱ “severely invasive category” in the list. Crayfish seems to have achieved partial victory in the invasion.
And another species called “marbled crayfish” seems to have a full blooming trend compared to the crayfish on the table. This is a lobster capable of parthenogenesis, discovered in German aquariums more than 20 years ago. The reason why it is eye-catching is not because it looks good, but because the owner of the aquarium found that after raising a marbled crayfish in the tank, he would harvest a whole tank of crayfish. Procambarus clarkii, which we often eat, requires at least one female and one male to reproduce normally, which is also the requirement for most species to reproduce.
Scientists have sequenced the genome of the marbled crayfish and found that its genome is triploid, that is, three sets of similar chromosomes, rather than the diploid of the general crayfish. Under normal circumstances, the two sets of chromosomes of a crayfish come from its father and mother. The chromosomes of the marbled crayfish are very similar to those of the American dragon crayfish (Procambarus fallax), and may be their offspring.
Researchers speculate that the ancestral chromosomes of a dragon crayfish left for the marbled crayfish copied once, leading toWhen combined with another dragon crayfish, there is one more group than normal shrimp.
The ID photo of the marbled crayfish (Image source: Franke Lyko 2017)
Ancestral chromosomes are not ancestral treasures, the more the better. There is no way to distribute the three sets of chromosomes equally, so there is no way to have sexual reproduction. However, this crayfish was so talented that it obtained the ability of parthenogenesis. Not only did it not die alone, but it reproduced countless offspring. Based on this, scientists named it “virgin lobster”(Procambarus virginalis).
Marbled crayfish has the characteristics that people look forward to: as long as there is one lobster, it is possible to have more lobsters. Although it is smaller than Procambarus clarkii and has less meat, it does not prevent the marbled lobster from turning into a delicious food from the ornamental animals in the aquarium.
Of course, it did not prevent the marbled crayfish from becoming an invasive creature like Procambarus clarkii. Without worldly desires, it spreads even more vigorously. In the ten years from 2007 to 2017, the marbled crayfish in Madagascar may have increased by 100 times, with the number of individuals reaching millions.
Marbled crayfish flooded in disasters (Image source: Julian Gutekunst et al. 2018)
hairy crabs: A hometown is better than a hometown
Coincidentally, American crayfish came to China and escaped from the table to commit crimes, while Chinese hairy crabs also went out of the country, conquered the South and North, and swept Europe and the United States.
The official Chinese name of hairy crabs is “Chinese mitten crab”, which is derived from the fluff on the crab claws.
The fluff on hairy crab tongs is very obvious (Image source: Christian Fischer, CC BY-SA 3.0)
Many inland people think that hairy crabs are completely freshwater crabs. Actually, although hairy crabs live in freshwater lakes or in the light salt water at the junction of rivers and seas most of their lives, their reproduction is closely related to the ocean. In the golden autumn, the yellow and fat hairy crabs descend from lakes and rivers to complete mating and spawning in the river estuary.
After the crab eggs hatch, they have undergone multiple molting and turned into juvenile crabs. They then began to swim upstream, enter the rivers and lakes where their ancestors lived, and began a life of arrogance and arrogance. According to this feature, in order to breed hairy crabs in the inland areas, the broodstock must be placed in a salt water pond for mating during the breeding season to simulate the marine environment.
This kind of river-sea migration, salty, salty and all-eat-all characteristics also allows hairy crabs to be widely distributed in the rivers and lakes connected to the sea in our country, which also provides innate convenience for its subsequent global journeys.
When a merchant ship is not loading, in order to maintain the stability of the hull, some sea water or river water will be pumped to the bottom cabin to increase the weight and reduce the center of gravity to prevent the ship from capsizing in wind and waves. When the cargo arrives at the destination, the merchant ship will discharge the ballast water again.This process allowed many aquatic organisms to free ride. Hairy crabs who are well versed in this way have also opened the way to global proliferation with the ballast water.
After taking a merchant ship to the estuary area of a foreign country offshore, the hairy crabs flowed into the local ocean with the ballast water. The confluence of river and sea water is just a suitable habitat for hairy crabs. Therefore, the offspring of hairy crabs, like their ancestors in China, follow the genetic guidance and follow the river up to the inland lakes of foreign countries.
As early as 1912, German fishermen had discovered hairy crabs in local rivers. Since then, hairy crabs have existed in Europe for hundreds of years, so that many people think they are native European species. After all, one hundred years ago, many people’s great-grandfathers may not have been born yet, and Chinese hairy crabs have already taken root in a foreign country.
Like crayfish, hairy crabs also went smoothly in the new environment, even better, defeating all the aborigines in one fell swoop, becoming the only local freshwater crab in Germany.
Humans: There is a price to pay for digging holes indiscriminately
Many people may think that invading organisms occupy the living space of native species and change the structure of the ecosystem. This matter seems to have nothing to do with us ordinary people. In fact, this kind of invasion will bring huge economic losses.
Crayfish and hairy crabs are both mouse-type invaders who are proficient in drilling holes. The World Cultural Heritage Hani Terraces collapsed because of the crayfish digging holes in the terraces. This not only led to a substantial reduction in rice production, but also damaged the proud local terraced landscape. The local government had to invest 1.1 million yuan to buy pesticides to eliminate crayfish.
(Picture source: Beijing Evening News)
The hairy crabs with migratory habits will go down the river during summer and autumn.Blocking up irrigation and drainage systems will have a great impact on local crop yields. In addition, when hairy crabs dig a large number of caves on the river bank and dam, it may cause the houses on the river bank to collapse, and even the dam may break. When domestic news mentions the invasion of edible species, including the two, they often say: If these are delivered to the Chinese, it will not only solve the local crisis, but also satisfy the Chinese people’s stomach. .
Unfortunately, the facts are often not that simple-If the elimination of an invasive species can be solved by eating alone, then why does it become an invasive species?
The lobsters and hairy crabs have mixed eating habits, and they are opportunists who come here and don’t want to eat. Large numbers, high reproduction rate, and strong environmental adaptability are advantages in the breeding industry, but when these characteristics appear in a combative alien species at the same time, the occurrence of biological invasion is almost inevitable.
Crayfish, which began to spread wildly in the country in the 1930s, began to be used as food after the 1960s. In 1983, researcher Dai Aiyun of the Institute of Zoology, Chinese Academy of Sciences began to advocate crayfish as a resource. use. After that, the appearance of “Thirteen Fragrant Crayfish” attracted countless gluttons. However, the crayfish was not quickly resolved because they were found to be delicious. On the contrary, because of its high economic value, large-scale farming produced more escape opportunities…
In foreign countries, German fishermen decided to sell hairy crabs to local Chinese restaurants, or simply export them directly to Asia. These “natural and wild” hairy crabs are not only inferior to the cultured species in taste, but even because of the added cost of transnational logistics and quarantine, there is no competitive advantage in price. Therefore, this seemingly two-fold solution eventually disappeared. The State of Maryland in the United States even issued a warrant for hairy crabs, calling on the people to hunt for hairy crabs, to see crabs alive, and corpses to die.
Maryland Hairy Crab Wanted Order (Image source: Chesapeake Bay Magazine)
However, for humans, these flood of invaders are not useless.
During the breeding process, due to the phenomenon of catching large ones and keeping small ones and inbreeding of seedlings, the size of cultivated crayfish and hairy crabs is getting smaller and smaller, and they are more prone to disease, and the germplasm is constantly degrading. The result is that the quality of these two organisms continues to decline, and the meat quality is not as delicious as before. And these shrimps, soldiers and crabs with their teeth and claws burrowing holes in the fields provide important genetic breeding resources for breeds with declining germplasm resources.
In other words, these escaping and flooding creatures experienced a cruel natural selection, their taste decreased, but they were better than artificially bred species in certain qualities, such as stronger disease resistance. Sex, which gives people the possibility of improving breeding individuals through hybridization and reversing the degradation of germplasm. The efforts made by the crayfish to fight for freedom have finally become the boosters for their kind to make their debut on the table.
References:
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This article is from WeChat official account:Science University (ID: kexuedayuan) , author: Lee ink spilled