It’s the MHC class I receptors that drive cytotoxic T cells to attack foreign cells in tissue transplant settings. First, they looked at genes that encode the fishes’ major histocompatibility complex (MHC) class I and II proteins, cell surface molecules that differ between individuals and enable T cells to distinguish the body’s own cells from foreign ones. The team examined a handful of well-characterized genes known to be key players in the adaptive immune response. The team also included three control species from other anglerfish groups in which males never attach to females. That included four species that mate by temporary attachment and six species that form permanent fusions-three of them in a one-to-one fashion, and three that have multiple males fuse with a single female. Biological samples from the deep sea are hard to come by, but with the help of ichthyologist Theodore Pietsch, an expert on deep-sea anglerfishes at the University of Washington, the team was able to obtain tissue samples from several specimen collections.īoehm and his colleagues sequenced the DNA from 31 specimens, representing 13 species of deep-sea anglerfish. Immunologist Thomas Boehm and his colleagues at the Max Planck Institute of Immunology and Epigenetics in Germany long wanted to know how some anglerfish species can form bodily fusions between individuals, and set out to do an analysis of the animals’ genomes. Evolution produces all sorts of wacky outcomes, and this is one of them.” “I suppose we shouldn’t have too many preconceptions about what is and isn’t possible in nature. “It’s quite shocking,” remarks geneticist Elizabeth Murchison of the University of Cambridge who wasn’t involved in the study. Over the course of evolution, changes in genes involved in antibody production and cytotoxic T cell responses may have paved the way for the animals’ strange reproductive habits, while for scientists it raises questions about how the fish defend themselves against pathogens in the deep sea. The genomes of species that temporarily or permanently fuse with their mates have undergone radical alterations of key genes that underpin adaptive immunity-a branch of the immune system responsible for the rejection of foreign tissue-making some of them the first known instances of vertebrates that effectively lack an adaptive immune system. Why don’t the female anglerfish, immunologically speaking, reject these parasitic males?Ī new genomic analysis of 13 anglerfish species published today (July 30) in Science provides some clues. In virtually all other adult vertebrates, introducing tissue from one individual into another would provoke a powerful immune response attacking the foreign cells. holboelli, males permanently “fuse” with females, or females absorb multiple males-in some cases up to eight at a time.Īmong the many mysteries surrounding these deep-sea rendezvous-they were only captured on camera for the first time in 2018-is an immunological one. In some species, males only temporarily attach to females and then part ways. The sub-order of deep-sea anglerfish, composed of nearly 170 known species, arguably displays the most dramatic mating habits in the animal kingdom. As he vanishes, two individuals become one-taking the concept of monogamy to a new level. Slowly, his body morphs into hers, his cells becoming hers, including his testicles, which are used to make offspring. Instead, the male-just a few inches long-clasps onto the comparatively gigantic female’s body and never lets go. Krøyer’s deep-sea anglerfish, Ceratias holboelli, does not spawn, copulate, or do anything a fish would ordinarily do to mate. ABOVE: A 75-mm-long Melanocetus johnsonii female with a 23.5-mm-long male attached to her belly
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