Effects of X-irradiation on colony specificity in the compound ascidian, Botryllus primigenus Oka

In a compound ascidian, Botryllus primigenus Oka, colony specificity or histoincompatibility has been known. Colony specificity is manifested by fusibility between colonies (fusion or nonfusion). It has been suggested that fusibility of a colony depends upon blood and that cellular and humoral factors may participate in the "nonfusion" reaction (NFR), which is induced in the contact area between two incompatible colonies. In the present study, effects of X-irradiation on colony specificity were studied. When the cut surfaces of two colony pieces previously irradiated were brought into contact, only weak NFR took place in the contact area, although fusion has never occurred. By the use of experimental alteration of fusibility, "fusibility alterable index" (FI) of the irradiated colonies were estimated. FI was inversely proportional to dose of X-irradiation. FI of a colony received 3,000 R corresponds to that of about one-fourth in size and FI of a colony received 5,000 R corresponds to that of about one-eighth in size. Therefore, a factor(s) controlling fusibility may be sensitive to X-irradiation.