TRANSMISSION GENETICS OF ALLORECOGNITION IN HYDRACTINIA-SYMBIOLONGICARPUS (CNIDARIA, HYDROZOA)

Allorecognition is ubiquitous, or nearly so, amongst colonial inverteb rates. Despite the prominent role that such phenomena have played both in evolutionary theory and in speculations on the origin of the verte brate immune system, unambiguous data on the transmission genetics of fusibility (i.e., the ability of two individuals to fuse upon tissue c ontact) is lacking for any metazoan outside of tile phylum Chordata. W e have developed lines of the hydroid Hydractinia symbiolongicarpus (P hylum Cnidaria) inbred for fusibility and here report results of breed ing experiments establishing that fusibility segregates as expected fo r a single locus with codominantly expressed alleles, with one shared allele producing a fusible phenotype. Surveys of fusibility in field p opulations and additional breeding experiments indicate the presence o f an extensive allele series.