A New Type of the Manifestation of Colony Specificity in the Compound Ascidian, Botrylloides violaceus Oka

¹ Shimoda Marine Research Center, University of Tsukuba, Shimoda 5-10-1, Shizuoka 415, Japan

A new type of colony specificity (= allogeneic recognition) is shown for Botrylloides violaceus. All botryllid ascidians previously studied for colony specificity show allo-recognition reactions, manifested as fusion or nonfusion (rejection), both at the colonial margin (= growing edge) and at the cut surface. By contrast allorecognition in Botrylloides violaceus is absent at the cut surface, but present at the growing edge. Juxtaposition of cut surfaces resulted in fusion of the colonies regardless of origin, while juxtaposition of natural growing edges resulted in fusion or rejection, according to the genetic combination of colonies. Similar results occurred among the sibling colonies derived from the same mother colony, in which pairs tunic necrosis was observed in areas where the two colonies partially fused. These features of allogeneic rejection in B. violaceus were very similar to those of "nonfusion" in Botrylloides simodensis. In inter-specific combinations between B. violaceus and B. simodensis, a remarkable necrotic reaction was observed in the zone of contact when two colonies touched at their cut surfaces. When brought into contact at their growing edges, they resulted in "nonfusion" without a particular reaction.

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