There are a few more strange animals than the angler, a species that has so much difficulty finding a mate that when males and females connect underwater, males actually attach their tissue to females for life. After the merger, the two share one respiratory and digestive system.
Now scientists have discovered that the anglerfish carry out this sexual parasitism because it has lost a major part of its immune system, which in turn allows two bodies to become one without tissue rejection. (Remember a symbiote of Jadzia Dax Deep Space Nine?)
All vertebrates, including humans, have two types of immune systems. The first is the intrinsic system, which responds quickly to attacks by microscopic invaders with a variety of chemicals such as mucous physical barriers such as hair and skin, and disease-depleting cells called macrophages. The second line of defense is an adaptive system that produces two “killer” T cells to attack the pathogen and custom-made antibodies to fight specific bacteria or viruses. The two systems work together to fight infections and prevent disease.
But in a study published Thursday in the journal Science, researchers from the Max Planck Institute in Germany and the University of Washington found that many species of anglerfish (there are more than 300) have evolved over time to lose the genes that control their adaptive immune systems, in meaning that they cannot create antibodies and decrease those T cells.
“Anglerfish have traded in their immune faculties, which we believe are essential, for this reproductive behavior,” says Thomas Boehm, a professor in the Department of the Institute of Immunobiology and Epigenetics in Freiburg, Germany, and lead author. on paper.
To reach this conclusion, Boehm and his colleagues have spent the past six years conducting genetic tests on samples of angler tissue taken from around the world. They tried to catch them using deep sea trawls to collect samples 1,000 feet below the surface, but because the angler is rare and elusive, they could not collect live samples. So to get enough tissue for their genetic analysis, the researchers instead deleted museum collections and other labs that had petri dishes cleaned in preservatives, some of them decades.
In the anglerfish family, there are several reproductive methods. Females of some species unite with one male; others join multiple men; and still another group have only a temporary merger. After beating 31 tissue samples of 10 species, the team performed genetic tests and found that species that temporarily mate with their peers do not have the genes responsible for antibody maturation. Species that create a permanent link with their friends have also lost a set of additional genes that are responsible for the assembly of T cell receptors and antibody genes that are the cornerstone of the innate immune system in all vertebrates.
“It was intuitive to think that there is any genetic proclivity that allows this to happen,” Boehm says of the unusual immune systems of the anglerfish species. “This is the first bit of evidence that these animals have this inability to reject a part of themselves and allow these matings to occur.”