ALLOIMMUNE RESPONSES BETWEEN ACROPORA-HEMPRICHI CONSPECIFICS - NONTRANSITIVE PATTERNS OF OVERGROWTH AND DELAYED CYTOTOXICITY

Allogeneic interactions between Acropora hemprichi (Ehrenberg) colonie s were followed in situ up to 18 mo between 1990 and 1992 in Eilat, Re d Sea. We established all 21 possible branch pair combinations among s even large colonies in three to eight replicates each (n = 92 pairs), in addition in 14 pairs of grafts within-colonies. All isografts resul ted in fusion. Allogeneic interactions revealed a variety of effector mechanisms which involved the appearance of dark blue-purple color in the tissues of interacting branch tips (< 1 cm), unilateral overgrowth s (1.0 to 1.5 mm mo-1 for 1 to 8 mo), rejections, healings, continuous overgrowths, reversals, repeated rejections and more. Direction of ov ergrowth was usually specific to a given combination of colonies. A hi erarchial network of overgrowths was obtained by analyzing overgrowth directions of all pairwise combinations, which included 30 transitive and five nontransitive three-way combinations. These outcomes, similar ly to responses of allogeneic encounters recorded from other coral spe cies, show that colonies can respond selectively to different types of allogeneic challenges. It is suggested that corals may have the capac ity to distinguish self from nonself by recognizing nonself attributes presented on conspecifics.