Enzyme Variation in Paramecium caudatum

Stocks of four “syngens” (syngens 1, 3, 12, 13) of Paramecium caudatum could not be distinguished on the basis of isozymic variations of six enzymes. Using the most common enzyme form as the standard for the syngen, we found a higher coefficient of identity between syngens (>90%) than within syngens (73%). These observations, combined with evidence for fertile matings among the groups, suggest that the groups do not warrant the status of syngens. True syngenic variation in P. caudatum is, however, clearly established on the basis of isozymic and breeding studies of wild stocks collected from various places. Some stocks from England have a close affinity with those from Japan, but stocks from Scotland and California must be placed in separate syngenic sets. Thus, P. caudatum is indeed a species complex, within which evolutionarily distinct groups (species = syngens) are identifiable. The definition of syngens on the basis of initial agglutination response is, however, unjustified.