Research Article

The immunogenetics of sexual parasitism

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Science  25 Sep 2020:
Vol. 369, Issue 6511, pp. 1608-1615
DOI: 10.1126/science.aaz9445

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Reconfiguring an immune response

The deep sea is a vast and generally empty environment. Finding a mate can thus be difficult. In response to this situation, one group of deep-sea denizens, the anglerfishes, have evolved a system in which males attach to females, in some cases permanently, through fusion of tissues and connection of circulatory systems. Such attachment greatly challenges the immune systems of the fish. Swann et al. found that these challenges have been met by the evolution of increasingly reduced immune responses among anglerfish species, including the loss of what have been considered essential vertebrate responses. These shifts suggest that vertebrate immune systems may be more flexible over evolutionary time than was previously thought.

Science, this issue p. 1608


Sexual parasitism has evolved as a distinctive mode of reproduction among deep-sea anglerfishes. The permanent attachment of males to host females observed in these species represents a form of anatomical joining, which is otherwise unknown in nature. Pronounced modifications to immune facilities are associated with this reproductive trait. The genomes of species with temporarily attaching males lack functional aicda genes that underpin affinity maturation of antibodies. Permanent attachment is associated with additional alterations, culminating in the loss of functional rag genes in some species, abolishing somatic diversification of antigen receptor genes, the hallmark of canonical adaptive immunity. In anglerfishes, coevolution of innate and adaptive immunity has been disentangled, implying that an alternative form of immunity supported the emergence of this evolutionarily successful group of vertebrates.

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