Adaptive immunity in invertebrates: a straw house without a mechanistic foundation

Recently claims have been made for radical new insights in the field of invertebrate immunology that involve memory, specificity and/or maternal transfer of immunocompetence. For evidence these claims rely on phenomena, such as survival or reproductive capacity, observed at the level of the whole organism. The allure of these apparently revelatory hypotheses is that they are contrary to established views of innate immunity. They draw implicit analogy to adaptive responses in jawed vertebrates and the terminology used creates an incomplete and misleading picture. We argue that the case for adaptive immunity in invertebrates based only on such phenomena is weak and flawed, as it can only be upheld if supported by descriptions of the underlying mechanisms. We caution against a reliance on this approach as a means of advancing this field-highlighting, as an example, some negative commercial implications of adopting this approach.