SHARED PRODUCTS. “The products of horizontally acquired microbes can be essential for a range of developmental functions, including influences on larval growth rate and body size in invertebrates, postembryonic maturation and renewal of epithelia in invertebrates and vertebrates, development and specification of the gut-associated lymphoid tissues in vertebrates, activation of the immune system in tsetse flies, and normal brain development in mammals.”
http://www.pnas.org/content/110/9/3229.full