Genetic evidence of self-fertilization in the sea anemone Epiactis prolifera

Biochemical genetic variation provided evidence for the mode of reproduction of brooded young in the sea anemone Epiactis prolifera Verrill, 1869. Individuals of E. prolifera are female when small but hermaphroditic when large (i.e., gynodioecious); juveniles are brooded externally on the column. Brooding individuals collected from 6 intertidal sites (5 in central California and 1 in Washington State, USA) in the spring and summer of 1980 were assayed for gene-enzyme variation by starch-gel electrophoresis. Three of 12 enzyme loci were polymorphic; phosphoglucose isomerase appeared to be encoded by two, closely linked loci. Genotypic frequencies deviated markedly from expected random mating proportions. Only three heterozygotes were found; two were heterozygous at all three polymorphic loci, and the other was polymorphic at the two PGI loci. All 158 juveniles from 25 brooding individuals were assayed (2–19 juveniles per parent). Juveniles on homozygous adults were always identical to their parent. However, brooded young of heterozygous individuals were not identical to their parent. but showed 1:2:1 phenotypic segregation ratios consistent with reproduction by self-fertilization. This genetic evidence together with findings of marked heterozygote deficiencies and genetic identity of homozygous adults and their brooded young supports the conclusion that E. prolifera usually reproduces by self-fertilization, and cross-fertilization is rate.