Fig. 10.

Proposed models of the evolutionary trajectory of the immune system in cold water-adapted Gadinae species. A Two possible scenarios are proposed to connect the relative timing and connection between the evolutionary events of the loss of many adaptive immune genes (e.g., mhc II and cd4), relief of natural selection to AID hotspot enrichment in Ig variable genes, and AID catalytic inactivation. B Cold water-adapted Gadinae species are unusual among bony fish and vertebrates in that they are missing many genes that are essential for a robust antibody response and contain an inactivated AID enzyme. On the other hand, they exhibit an expansion of other genes involved in cell-mediated and innate immunity