Self and Non-Self Recognition in a Calcareous Sponge, Leucandra abratsbo

Discrimination between self and non-self has been shown in many demosponges, but calcareous sponges have not been studied. Allorecognition in a calcareous sponge, Leucandra abratsbo, was analyzed in allogeneic combination assays. Most allogeneic combinations were incompatible, and the low rate (4.8%) of allogeneic acceptances suggests an extensive polymorphism in those genes that may control allorecognition. However, histological studies of the rejection process revealed that the first reaction consisted of strong adhesion of allogeneic pieces. Thereafter, the rejection reaction that followed was accompanied by the accumulation of archeocytes in the contact region. Vigorous cytotoxic reactions occurred within this region, and the degenerated cells were probably phagocytosed by archeocytes, which suggests that they are the primary effector cells for cytotoxicity and phagocytosis. Because L. abratsbo is a solitary sponge, armed with protruding spicules that prevent contact of the pinacoderm with that of conspecific individuals, allorecognition may not prevent the formation of allogeneic chimeras in the natural habitat.