ALLORECOGNITION RESPONSES IN THE SOFT CORAL PARERYTHROPODIUM-FULVUM-FULVUM FROM THE RED-SEA

Allogeneic encounters were experimentally arranged in Eilat, Red Sea f or the first time in the Alcyonacea with the soft coral Parerythropodi um fulvum fulvum. All possible pairwise combination assays within two groups of five colonies each and one group of three colonies were setu p in situ in 2-4 replicates each (a total of 76 assays). Control isoge neic encounters always resulted in complete tissue fusion. Two types o f allogeneic responses were documented following tissue-to-tissue cont acts. The first was retreat growth, in which contacting allografts sta rted to retreat from each other a few days following direct contact un til a bare area of a few mm separated them. In several assays the colo nies repeatedly grew into contact and retreated again. The second allo geneic response was unilateral or reciprocal tissue overgrowth. In thi s type of response one colony overgrew the conspecific partner by seve ral mm and then stopped. The underlying tissue of the overgrown partne r died. No cytotoxicity was observed in allogeneic contacts either in growing parts or when assays were established between cut surface area s. Repeated assays of the same pair-combination were not consistent in terms of type and directionality of responses. We propose that effect or mechanisms elicited following allogeneic encounters in P. f. fulvum may be affected by biological as well as non-biological parameters an d are not specific to the type of allogeneic challenge. However, colon y specificity in this species is restricted only to the level of self- and non-self discrimination.