The 100-year-old mystery of "connected couples" has been solved.

!-- ewebeditor:page title"--You may have seen a catfish in the animated film "Underwater Mobilization", a squinting, glowing deep-sea monster fish.
a glowing part of the female's forehead that looks like a pole with a light bulb, which contains glowing bacteria.
these glowing experiences attract both prey and potential mates to them.
, in fact, these are nothing, incredible is the breeding strategy of herring: female and male fish "blood and flesh fusion", co-prosperity symbonity.
unusual phenomenon is known as "gender parasitic".
the phenomenon of "gender parasites" has been a mystery for 100 years since Icelandic biologists discovered the first con company fish in 1920.
now, German and American scientists have solved this 100-year-old problem, published in Science.
" is that it is difficult to collect well-preserved organizations to conduct the necessary research.
study's correspondent, Thomas Boehm, director of the Institute of Immunobiology and empticontology at the Marp Society, told the Chinese Journal of Science.
researchers sequenced the DNA of frozen tissue specimens covering a wide range of non-adhesion, temporary adhesion, and permanent adhesion of herring species.
researchers found that fusion species changed dramatically in the composition and structure of key immune system genes compared to species that did not have attachment fusion.
has led researchers to gain a better understanding of the immune system and help develop treatments for immunodeficiency patients.
Couples" one fish, also known as , is known to have 168 species that live deep in the ocean below 300 metres and have evolved some remarkable adaptability, the most revealing of which is the way couples get along.
people first discovered the creature, they were surprised that almost all of the fish were female.
and almost all of the females have strange "lumps".
later, it was discovered that the lumps were male fish.
in order to survive, male herring bites the female when it encounters it and binds to it.
male fish are usually less than 10 mm long, attached to larger females and mated through this sex parasite.
For some species of herring, this attachment is temporary, while others are permanent: the skin tissues of the two fish fuse, and eventually their circulatory systems connect to truly become "one" couple.
researchers say the permanent union of female and male fish represents an anatomical union that is almost unknown in nature, except in genetically identical twins.
immune system is a common barrier that attacks foreign tissues like cells infected with pathogens.
but why does the female's immune system turn a blind eye to "foreign invaders"? In other vertebrates, tissue fusion triggers a significant immune response, which is why people must take immunosuppressive drugs after receiving an organ transplant.
Boehm always wanted to know how the catfish did it.
a few years ago, Boehm and the herring expert, Theodore W. Pietsch of the University of Washington in Seattle, set out to study the genomes of different herring species.
they studied the structure of major tissue compatibility (MHC) antigens.
these molecules are present on the surface of human cells, which alert the immune system when they are infected by a virus or bacteria.
to ensure that all pathogens are effectively identified, the diversity of MHC molecules is so high that it is difficult to find the same or near-identical form in any two individuals of the same species.
is also the root cause of tissue matching problems in human organs and bone marrow transplants.
researchers analyzed the DNA of 31 herring specimens from 10 species and found that the fused herring species lacked key immune system genes.
researchers say the genes that encode these MHC molecules in permanently attached herring have largely lost their independence, as if they had abandoned immune recognition for tissue fusion.
in addition to this unusual combination of MHC genes, we found that during organ rejection, the function of killer T-cells, which are usually actively removed from infected cells or attacking foreign tissue, is also severely impaired.
findings suggest that the immune system of mackerel is unusual among thousands of vertebrates.
study's lead author, Jeremy Swann of the Institute of Immunobiology and Eigenetics at the Marp Society.
these unexpected findings, scientists suspect that the recombination of the herring's immune system may be broader than expected.
fact, further studies have shown that antibodies, the second most powerful weapon in the immune defense arsenal, have also disappeared in some mackerel species.
, the researchers concluded that the animals used improved congenitations to protect themselves from infection, an unexpected approach.
fact, until now, it has been thought that once a partnership between innational and innitive immunity has evolved, it is not possible to get rid of this relationship, with serious consequences.
Therefore, this study shows that vertebrates can survive without adaptive immune function, despite the co-evolution of innitive immune and adaptive function over several hundred million years, which was previously considered irreplaceable.
the third parasite in addition to the "husband", herring and luminescent bacteria are also symbication.
another group of researchers had previously found that the bacteria had lost some of the genes needed to survive freely in the water.
related papers published in mBio.
In particularly interesting is the evidence that this evolution is still ongoing and that bacteria are still losing genes, and the reasons are not clear," said Tory Hendry, a microbiologist at Cornell University and lead author of the paper.
"The symbication relationship between most known organisms and bacteria is either host and free-living bacteria that cannot evolve to maintain symbly relationships, or host and in-cell bacteria, which live in host cells and significantly reduce the genome during evolution.
that the herring and bacteria represent a third symbymbic relationship, and preliminary data suggest that these bacteria may have been transferred from the herring to the water.
"this is a new example of symbic relationships in which bacteria are not actually trapped by hosts, but they are evolving."
," Hendry told reporters.
!--/ewebeditor:page-!--ewebeditor:page title"--gene sequencing shows that the genomes of these glowing bacteria are 50 percent smaller than those of their free-flowing relatives and have lost most of the genes associated with making amino acids and breaking down nutrients other than glucose.
, they have a complete path to form whiplash -- a spiral tail that moves through the water.
other hand, Boehm and others believe they have even caught a fish that is developing into a gender parasitic.
Pietsch said: "It is noteworthy that in this fish, unusual breeding methods have been independently 'invented' several times.
" but how they evolved these breeding methods is not yet known.
" is complex and requires more research.
," Boehm said.
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