The researchers analyzed the genomes of ten species of deep-sea angler fish and found that some species have lost the ability to develop acquired immunity. The reason is the unusual breeding strategy of these fish: their dwarf males attached to the females and in some cases even fused with them. To avoid rejection of partners, anglers have to abandon many of the immune mechanisms, and in the most extreme cases we are talking about the complete disappearance of the acquired immune system. In an article for the journal Science , scientists recognizethat don’t know how the fish is able to protect itself from diseases and pathogens.
Deep-sea animals is quite difficult to find a partner for reproduction, but a unique solution to this problem was developed anglerfish of the suborder Ceratioidei. The males of these fish evolved into dwarfs, which are attached to the female after meeting her. In some cases, the angler is a male after some time returned to a free life, but among the most specialized types of partners remain together for life, grow together the circulatory systems. Sometimes the female bears several parasitic males.
Scientists have long wondered why the immune system of a female anglerfish do not perceive the male as a foreign object and kills it. There is an assumption that anglers reduce the risk of rejection by the smell of choosing the most genetically similar partner. According to another explanation, the genetic diversity of deep-sea angler fish are so low that the fusion of the male and females leads to a strong immune response.
To understand this issue decided by a team of specialists led Swanna Jeremy (Jeremy B. Swann) from the Institute of Immunobiology and epigenetics the max Planck Society. The researchers analyzed the genomes of 31 individuals of the deep-sea angler fish, which belonged to ten species from different families. The studied species have different strategies of breeding: in four, the male attaches to the female temporarily, from three to one female parasite is constantly one male and three one female can carry multiple males of permanent freeloaders. As an external control, the researchers used three species of anglerfish from the suborders clonogenic (Antennarioidei) and Hanukovich (Chaunacoidei), males which have normal sizes.
The researchers focused on genes related to the work of acquired immunity. It turned out that the unusual reproductive strategy significantly weakened the immune system of deep-sea angler fish, and these changes were symmetrical in females and males.
Even species that form temporary relationships with partners, rejected part of the immune mechanisms based on the use of antibodies. This is evidenced by damage in a gene aicda, which regulates the maturation of antibodies. From parasitic angler fish, in addition, suffered and cellular immunity: as a result of changes in the genes of the major histocompatibility complex and the loss of two genes of receptors of T-lymphocytes were partially or completely lost cytotoxic activity of immune cells.
As the analysis has shown, the stronger the connection between female and males, the weaker the immune system the angler. If you temporarily fixed types was sufficient to partially suppress antibody production, the anglerfish, whose females bear several males, completely abandoned acquired immunity. Such extreme adaptation was demonstrated in two of the studied species, Photocorynus spiniceps and Haplophryne mollis. Among other things, they have stopped working genes RAGinvolved in the production of antibodies. It is believed that they originated about 500 million years ago and since then are present in all vertebrates.
If similar losses faced a mammal, it would have died as a result of severe immunodeficiency. However, anglers have managed to survive despite the fact that they too are faced with bacteria and parasites. Scientists suggest that these fish cost the innate immune system or use of specific protective mechanisms, for example based on proteins of the interferons.
According to the authors, parasitic males occurred independently in several evolutionary lines of anglers. This means that corresponding changes in the genes responsible for acquired immunity, occurred repeatedly. Most likely, the first type of angler losing some of these genes and then started to practice knitting with partners.
Unusual strategy of reproduction and the absence of acquired immunity is not the only unusual features of deep-sea fishes. Some of them acquired sorcery the skin, which represents 99.96 percent of incident light. According to scientists, this coloration allows it to hide from predators or sneak up to the victim.
Sergey Knee High