Scientists have now found that deep-sea anglerfish has evolved a mode of sexual parasitism for reproduction. According to a study published in the journal Science, males of the species permanently attach themselves to females through a form of anatomical joining, otherwise not seen in nature.
The tiny male anglerfish fuses its tissues to a more massive female during copulation, allowing the two to share not only sperm, but even blood and skin.
While earlier it was not known how the two manage to avoid being rejected by each other’s immune systems, the new study finds that some of the anglerfish species lack key genes which make fusion without consequences possible.
In vertebrates, immune protection involves a bodily response called adaptive immunity that identifies a foreign threat and then work towards eliminating it. Thus a risk remains in times of organ transplants. However, the missing genes of deep-sea anglerfish make the fusion possible.
Thomas Boehm, an immunologist at the Max Planck Institute of Immunobiology and Epigenetics in Freiburg, and colleagues managed to isolate DNA from 31 preserved anglerfish representing 10 deep-sea species. They found that in four of those species, males attach to the females temporarily while in the other six, the fusion is permanent. The same was not observed in shallow waters.
According to Boehm, species of anglerfish that fuse are missing antibodies, including genes that make the parts of T cells that help identify foreign tissues and pathogens.
As per the report, in anglerfish species – Photocorynus spiniceps and Haplophryne mollis– where multiple males can attach to a single female, antibodies may not be formed at all.
Boehm adds, “If I had to diagnose [those two fish] … I would say, ‘OK, this is red alert, we really have to do something because this is severe combined immunodeficiency. Fatal prognosis.”
The study highlights the various forms creatures’ immune systems can take, hinting that it is possible that anglerfish have an adaptive immune system that is completely different from other vertebrates.